***Useful Information For The Working Sparky***

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Polarity : ( Competent Person ) ( Dead Test ) Apprentice : you'll get some Q/A on 17th Edition

Polarity tests are made to verify that every fuse or single-pole device is connected in the Phase Conductor Only , ( 612.6 )
> Edison screw lampholders should be connected so that the Phase conductor is connected to the Centre contact : <
Lampholders to BS-EN 60238 . in circuits having an earthed Neutral conductor , centre contact bayonet and Edison screw lampholders have the outer or screwed contacts connected to the Neutral conductor ( 612.6 (ii)


The Tests should be Carried Out before the Installation is Energised Using a Low-Reading Ohmmeter or Continuity Test Instrument ,
Much of the Polarity Testing can be Carried Out during the process of testing CPC continuity by using the ( R1 + R2 ) method .
However Polarity should also be confirmed after connection of Supply ,

Earth Fault Loop Impedance ( External to the Installation ) ( 612.9 ) ≈ ≈ ( Live Test ) ≈ ≈ ***
The external earth fault loop impedance ( Ze ) is one of the Supply characteristics to be recorded ( Ze ) can Only be measured by testing at the Origin of the Installation . “ Before Testing “ ( The Earthing Conductor must be Disconnected from
The Main Earthing Terminal and the Entire Installation must be Isolated from the Supply ,
The purpose of Disconnecting the Earthing conductor is to ensure that measurement is not affected by Parallel Paths of , for Example :
The Main Bonding Conductors . The Instrument to be Used is an Earth Fault Loop Impedance Test Instrument :

The procedure is as follows :
* open the main switch :
* disconnect the earthing conductor :
* check test instrument and leads :
* apply test probes to the live side of the main switch and disconnected earthing connection :
* check polarity indication for correct connection :
* press the test button and record results :
* reconnect the earthing conductor must be disconnected from the main earthing terminal and the entire installation must be isolated from the supply ,
The purpose of disconnecting the earthing conductor is to ensure that measurement is not affected by Parallel Paths of , for Example .
The Main Bonding Conductors . The instrument to be used is an Earth Fault Loop Impedance test instrument ,

The procedure is as follows :
* open the main switch :
* disconnect the earthing conductor :
* check test instrument and leads :
* apply test probes to the live side of the main switch and disconnected earthing conductor :
* check polarity indication for correct connection :
* press the test button and record result :
* reconnect the earthing conductor before restoring the Supply :

Circuit Impedance Measurement :
The type of instrument to be used is the same as that used for external impedance testing , The earth loop impedance ( Zs ) of every circuit should be measured at the point furthest from the incoming Supply ,
The test must be undertaken with all protective conductors connected :

Prospective Fault Current : ( 612.11 ) ≈ ≈ ( Live Test ) ≈ ≈ ***
This is the largest current that would flow in the event of a fault between live conductors or between a live conductor and the earthing conductor . the value should only be measured at the origin of the installation .
Only the largest value is recorded The earthing conductor , main bonding conductor and CPC should all be connected .
The instrument used is an earth fault loop impedance test instrument with a prospective fault current range ,

A Polarity Check should also be made on Incoming Supply : ( PS: I don’t know if you still get this at Collage ) ≈ ≈ Live Testing , ≈ ≈

Continuity of Protective Conductors . ( 612.2.1 ) GN-3 ( Dead Test )
Main & Supplementary Equipotential Bonding :

There are Two options for Undertaking this Continuity Test : ( R1 + R2 ) method (1) or wander lead ( R2 ) only method (2)

When testing for continuity of main and Supplementary Equipotential Bonding , it is usual to apply the ( R2 ) only test ,
Before carrying out this test to confirm continuity of the appropriate bonding conductor ,
It is necessary to avoid the measurement of parallel paths ,
Accordingly: it is advisable to disconnect one end of the bonding conductor to be tested and any intermediate connections with services .
The wander lead method is undertaken by connecting one lead of the test instrument to the main earthing terminal with a long lead ,
With this long lead and the other lead of the instrument , make connection at the remote end of the bonding conductor .
Remember to Null the test leads of their instrument for this test , otherwise the measured value will include the résistance of the wander lead ,
It is also important to remember to Re-Null the test leads of the instrument only when the ( R2 ) test is completed ,
Otherwise , again the measured value would give an incorrect measurement ,
The ( R1 + R2 ) method applies to circuit protective conductors and their associated phase conductor ,
The Procedure is as follows :
* Isolate the Supply :
* Connect the phase & cpc conductors together at the distribution board :
* Measure the résistance between phase and cpc at each outlet or point :
* Measure and record the résistance between phase & cpc at the furthest point :
* Remove the temporary phase / cpc connection :

The ( R1 + R2 ) method can also be used to check the polarity of each circuit .
When testing ( R1 + R2 ) at each point it is also necessary to operate the switch in order to confirm an open circuit condition
When the switch is in the off position , therefore confirming polarity ,

Continuity of Ring Final Circuit Conductors :
Requires five distinct steps to be undertaken . The confirmation of continuity of ring final circuits
( Unfortunately some contractors appear to omit steps 2 , 3 , 4 , ) the procedures are as follows :

Step 1 : ( Checking Continuity of Live and Protective Conductors of a Ring Final Circuit ) ↔ ( little r1 & r1 : r n & r n : cpc & cpc )
Conductor Continuity
Isolate the Supply ,
Measure the résistance of the End–to–End Phase , Neutral and Circuit Protective Conductors Separately And record the values ,
The values of the Phase & Neutral conductors will indicate whether or not the conductors are continuous ,
Moreover , the Phase & Neutral conductors should have the same value of résistance .
The results taken should be recorded as ( r1 , r n & r2 , ) Schedule of Test Results include the provision for recording
Such measurements , then a ( tick ) should be entered in the column marked Ring .

Step 2a : ( Ring Final Circuit with No Spur ) Lead on Line & Neutral / Lead on Line & Neutral :
Phase-to-Neutral :
Connect the incoming Neutral to the outgoing Phase of the circuit and vice versa , Measure the résistance between the pairs
And note the results , The reading obtained should be half that obtained for either the Phase or Neutral conductor in Step 1 :

Step 2b :
Measure between Phase & Neutral at each point on the Ring Circuit .The readings should be much the same as in step ( 2a )
Sockets wired as spurs will give a slightly higher reading , Schedule of Test Results include the provision for recording
Step 3 :
Phase-to-Earth :
Repeat steps 2a & 2b but using the Phase and CPC conductors , This test also confirms polarity , The highest value obtained should be recorded in the ( R1 + R2 ) column ,
Step 4 :
Reconnect the conductors :
Insulation résistance , Before proceeding with this Test it must be ensured that all equipment vulnerable to an insulation résistance test
Has been disconnected , The Insulation is normally measured between Live conductors and Live conductors to Earth
The procedure for insulation résistance testing between Live conductors is as follows :
* Isolate the Supply :
* Disconnect all current using equipment and close all switches :
* Disconnect equipment vulnerable to a test
* Check instrument and leads :
* Select test voltage range :
* Connect the instrument and record values of Phase to Neutral between Phases , and Phases to Neutral for ( 3 Phase-Supply ) and
Between Live conductors :

Step 3 : ( Ring Final Circuits with No Spur )
Step 4 : ( Ring Final Circuits with Unintentional Spurs )

 

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“ Résistance and the Conductor “ 2392-10 : -&- you will be asked something like this Q/A

Résistance is directly proportional to length and inversely proportional to C.S.A. simply this means that More Length > More Résistance ,
and Less Length > Less Résistance , Also the Greater the C.S.A. the Less the Résistance , and the Smaller the C.S.A. the Greater the Résistance ,

"WHEN YOU GO TO WORK GUYS LOOK OUT FOR YOUR SELF AND YOUR PARTNER"

"PLAN ON STAYING ALIVE"

There are Proper Procedures that we all Should Follow when Working on Potentially Live Equipment. Testing Dead and Locking Off should be something that we do as a habit, and Remember to always Check your Tester on a Live Circuit before Using it to Test a Circuit Dead. Unfortunatly some Foremen and Contractors seem to forget that if One of Us gets Seriously Hurt or Killed in Order for them to get a Job Done Faster or Cheaper they are Liable and will be Prosecuted. Remember NOT Taking Chances is how “ Young Electricians get to be Old Electricians :

! Don't be a hero and stay alive !

Regulations : 12 / 13 / 14 / 16

Changes in the 17th Edition Jason can you move it to the right place Amberleaf

NOTE 1: This is not an exhaustive list.
NOTE 2: Particular attention is drawn to Section 701. This section now allows socket-outlets (other than SELV and shaver supply units to BS-EN 61558-2-5 ) to be installed in locations containing a bath or shower 3m horizontally beyond the boundary of zone 1.
• Regulation 131.6 – adds requirements to protect against voltage disturbances and implement measures against electromagnetic influences. In doing so, the design shall take into consideration the anticipated electromagnetic emissions, generated by the installation or the installed equipment, which shall be suitable for the current-using equipment used with, or connected to, the installation.
• Regulation 132.13 – requires that documentation for the electrical installation, including that required by Chapter 51, Part 6 and Part 7, is provided for every electrical installation.
• Chapter 35 – Safety services, recognizes the need for safety services as they are frequently regulated by statutory authorities whose requirements have to be observed, e.g. emergency escape lighting, fire alarm systems, installations for fire pumps, fire rescue service lifts, smoke and heat extraction equipment.
• Chapter 36 – Continuity of service, requires that an assessment be made for each circuit of any need for continuity of service considered necessary during the intended life of the installation.
• Chapter 41 – Protection against electric shock, now refers to basic protection, which is protection under normal conditions (previously referred to as protection against direct contact), and fault protection, which is protection under fault conditions (previously referred to as protection against indirect contact).
- Chapter 41 now includes those requirements previously given in Section 471 of BS 7671:2001.
- Chapter 41 now requires that for the protective measure of automatic disconnection of supply for an a.c. system, additional protection by means of an RCD with a rated residual operating current (IΔn) not exceeding 30 mA and an operating time not exceeding 40 ms at a residual current of 5 IΔn be provided for socket-outlets with a rated current not exceeding 20 A that are for use by ordinary persons and are intended for general use, and for mobile equipment with a current rating not exceeding 32 A for use outdoors. This additional protection is now to be provided in the event of failure of the provision for basic protection and/or the provision for fault protection or carelessness by users of the installation.
- Note that certain exceptions are permitted – refer to Regulation 411.3.3.
- Chapter 41 includes Tables: Table 41.2, Table 41.3 and Table 41.4 for earth fault loop impedances (replacing Tables Table 41B1, Table 41B2 and Table 41D). These new tables are based on a nominal voltage of 230 V (not 240 V), hence the values are slightly reduced. It has been clarified that where an RCBO is referred to in these Tables, the overcurrent characteristic of the device is being considered.
- Chapter 41 includes a new Table 41.5 giving maximum values of earth fault loop impedance for RCDs to BS EN 61008-1 and BS EN 61009-1.
- FELV is recognised as a protective measure and the new requirements are detailed in Regulation 411.7.
- Chapter 41 includes the UK reduced low voltage system. Requirements are given in Regulation 411.8.

• Chapter 42 - Protection against thermal effects, includes requirements in Section 422 Precautions where particular risks of fire exist (These requirements were previously stated in Section 482 of BS 7671:2001).
• Chapter 43 - Protection against overcurrent, includes those requirements previously given in Section 473 of BS 7671:2001. Information on the overcurrent protection of conductors in parallel is given in Appendix 10.
• Chapter 44 - Protection against voltage disturbances, includes a new Section 442, Protection of low voltage installations against temporary overvoltages due to earth faults in the high voltage system and due to faults in the low voltage system. This new section provides for the safety of the low voltage system under fault conditions including faults in the high voltage system, loss of the supply neutral in the low voltage system and short-circuit between a line conductor and neutral in the low voltage installation.
• Section 443 - Protection against overvoltages of atmospheric origin or due to switching, retains the existing text from BS 7671 and adds regulations enabling designers to use a risk assessment approach when designing installations which may be susceptible to overvoltages of atmospheric origin.
• Chapter 52 - Selection and erection of wiring systems, now includes busbar trunking systems and powertrack systems.
- It is now required to protect cables concealed in a wall or partition (at a depth of less than 50 mm) by a 30 mA RCD where the installation is not intended to be under the supervision of a skilled or instructed person, if the normal methods of protection including use of cables with an earthed metallic covering, mechanical protection (including use of cables with an earthed metallic covering, or mechanical protection) cannot be employed. This applies to a cable in a partition where the construction includes metallic parts other than fixings irrespective of the depth of the cable.
- Table 52.2 Cable surrounded by thermal insulation, gives slightly reduced derating factors, to take account of the availability of material with improved thermal insulation.
• Chapter 53 – Protection, isolation, switching, control and monitoring. Simplification means that requirements previously in Chapter 46, Sections 476 and 537 of BS 7671:2001 are now in this single chapter. Chapter 53 also includes a new Section 532 Devices for protection against the risk of fire, and a new Section 538 Monitoring devices.
• Chapter 54 - Earthing arrangements and protective conductors. The requirement that a metallic pipe of a water utility supply shall not be used as an earth electrode

 

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is retained in Regulation 542.2.4 which also states that other metallic water supply pipework shall not be used as an earth electrode unless precautions are taken against its removal and it has been considered for such a use. An example of other metallic water supply pipework could be a privately owned water supply network.
- A note to Regulation 543.4.1 states that in Great Britain, regulation 8(4) of the Electricity Safety, Quality and Continuity Regulations 2002 prohibits the use of PEN conductors in consumers’ installations. Regulation 543.7 has earthing requirements for the installation of equipment having high protective conductor currents, previously in Section 607 of BS 7671:2001.
• Chapter 55 - Other equipment, includes new additional requirements in Regulation 551.7 to ensure the safe connection of low voltage generating sets including small-scale embedded generators (SSEGs).
• Section 559 - Luminaires and lighting installations, is a new series of Regulations giving requirements for fixed lighting installations, outdoor lighting installations, extra-low voltage lighting installations, lighting for display stands and highway power supplies and street furniture (previously in Section 611 of BS 7671:2001).
• Chapter 56 - Safety services, has been expanded in line with IEC standardization.
• Part 6 - Inspection and testing, was Part 7 of BS 7671:2001. Changes have been made to the requirements for insulation resistance; when testing SELV and PELV circuits at 250 V, the minimum insulation resistance is raised to 0.5 MΩ; for systems up to and including 500 V, including FELV, the minimum insulation resistance is raised to 1.0 MΩ.
• Part 7 - Special installations or locations, was Part 6 of BS 7671:2001. The structure of Part 7 includes the following changes.
- Section 607 in BS 7671:2001 relating to high protective conductor currents has been incorporated into Chapter 54.
- Section 608 in BS 7671:2001 relating to caravans, motor caravans and caravan parks has been incorporated into
- Section 708: Electrical installations in caravan/camping parks and similar locations and Section 721: Electrical installations in caravans and motor caravans.
- Section 611 in BS 7671:2001 relating to highway power supplies is now incorporated into Section 559.
- The following major changes are incorporated in Part 7:
~~ Section 701 Locations containing a bath tub or shower basin.
~~ Zone 3 is no longer defined.
~~ Each circuit in the special location must have 30 mA RCD protection.
~~ Supplementary bonding is no longer required providing the installation has main bonding in accordance with Chapter 41.
~~ This section now allows socket-outlets (other than SELV and shaver supply units to BS EN 61558-2-5) to be installed in locations containing a bath or shower 3m horizontally beyond the boundary of zone 1.
• Section 702 - Swimming pools and other basins. This special location now includes basins of fountains. Zones A, B and C in BS 7671:2001 are replaced by zones 0, 1 and 2.
• Section 703 - Rooms and cabins containing sauna heaters. Zones A, B, C and D in BS 7671:2001 are replaced by zones 1, 2 and 3 (with changed dimensions).

• Section 704 - Construction and demolition site installations. The reduced disconnection times (0.2 s) and the 25 V equation no longer appear.
• Section 705 - Agricultural and horticultural premises. The reduced disconnection times (0.2 s) and the 25 V equation no longer appear. Additional requirements applicable to life support systems are included.
• Section 706 - Conducting locations with restricted movement, was Section 606 in BS 7671:2001.
• Section 708 - Electrical installations in caravan/camping parks and similar locations, now includes the requirement that each socket-outlet must be provided individually with overcurrent and RCD protection.
The following new sections are now included in Part 7:
• Section 709 - Marinas and similar locations
• Section 711 - Exhibitions, shows and stands
• Section 712 - Solar photovoltaic (pv) power supply systems
• Section 717 - Mobile or transportable units
• Section 721 - Electrical installations in caravans and motor caravans – previously in Section 608 of BS 7671:2001
• Section 740 - Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses
• Section 753 - Floor and ceiling heating systems.
Appropriate changes have been made to Appendices 1 to 7, in particular the methods and tables used in Appendix 4.

Earth Loop Impedance and Prospective Short Circuit (PSC) Testing Methods

Why Earth Fault Loop Impedance Test is Necessary ?

Earth fault loop impedance is the path followed by fault current when a low impedance fault occurs between the phase conductor and earth, i.e. "earth fault loop". Fault current is driven round the
loop by the supply voltage. The higher the impedance, the lower the fault current will be and the longer it will take for the circuit protection to operate.

To make sure the protection operates fast enough, the loop impedance must be low. Every circuit must be tested to make sure that the actual loop impedance does not exceed that specified for the protective device concerned. It is recommended that the (Ze) test be done first. This test, done at the distribution board, gives the loop impedance of the circuit, excluding the installation. The (Zs ) test, which includes the circuit tested in the (Ze) test as well as including the installation resistance, must be done next.

In most homes, basic shock protection is done by coordinating an earthing circuit with automatic switches in the indoor wiring circuits. This quickly cuts off supply to an earthing circuit where a fault occurs and touch voltage exceeds an acceptable limit. Proper protection against electric shock hazards is given when the TT wiring system complies with: Ra x Ia <50, where Ra is the sum of the resistances of earth bars and protective conductors and Ia is the maximum current of the protection system. Ra multiplied by Ia should not be more than 50 V, i.e. the maximum voltage one can touch will not exceed 50 V in the event of an earth fault.

Earth Fault Loop Impedance Testing :

The value of the earth fault loop impedance is the sum of transformer coil winding resistance, phase conductor (L1) resistance and the protective conductor (PE) resistance as well as the source earth resistance and installation resistance.
The Ze earth fault loop impedance measurement is made on the supply side of the distribution board and the main means of earthing, with the main switch open and all circuits isolated. The means of earthing will be isolated from the installation's earthing system (earth rods) bonding during the test. The Ze measurement will confirm the earth fault loop impedance as the sum of the resistances of the transformer coil winding, phase conductor or supply side and protective conductor resistance, but not the installation earth resistance

The Zs earth fault loop impedance should be tested at the furthest point of each circuit. In most cases the circuit breaker needs to be bridged out. The total earth fault loop impedance can be measured by plugging a loop tester into a socket outlet, or in some cases with an external earth probe. The value of the earth fault loop impedance is the sum of the resistances of the transformer coil winding , phase conductor (L1) and protective conductor (PE) as well as source earth and installation earth resistance.
When using an external earth probe, the earth fault loop impedance can be measured by touching an external probe directly to an earth bar, collector and connection point of an earth bar. The same measurement can be done by touching the earth probe to exposed, conductive parts of equipment in the circuits and exposed metal parts.

Prospective short circuit current (PSC) testing
The prospective short circuit or fault current at any point in an electrical installation is the current that would flow in the circuit if no circuit protection operated and a complete (very low impedance) short circuit occurred. The value of this fault current is determined by the supply voltage and the impedance of the path taken by the fault current. Measurement of PSC can be used to check that protective devices within the system will operate within safety limits and as per the safe design of the installation. ( PSC ) is normally measured between the Phase and Neutral at the DB or at a socket outlet.

 

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2391-10 : Use the wording

Routine Electrical Inspection and Report-( sometimes known as Home buyers or sellers Report)

Electrical installations should not be left without any attention for the periods of years between formal periodic inspections. Also not everyone may require a formal periodic inspection; you may wish to choose a less comprehensive routine electrical inspection instead. Typically these are required in the years between periodic inspections to monitor for deterioration, or to assess condition before or after house purchase, or if you know the wiring to be relatively modern and did not require extensive testing.
The following is a list of what is covered in the inspection:

Visual inspection
o Main protective bonding bonding conductor
o Supplementary protective bonding conductor ( where required )
o Breakages or damage
o Wear or deterioration
o Overheating
o Missing parts
o Switchgear obstructions
o Security of enclosures
o Adequate labelling
o Loose fittings

Function test
o Switchgear
o Equipment switching
o Circuit breakers

Test
o RCD trip times
o Earthing (loop impedance) and Polarity of ring and radial socket circuits

Reports

On completion of the inspection a report will be provided, detailing the condition of the installation, results of tests carried out, any recommendations and conclusions as to the relative safety of the installation.

Cost- Domestic – Homes only


Domestic- Homes …………………………………………........ £ Please contact us for prices ,
Additional Consumer-Units ….. i.e. Garage … etc ………. £ Please contact us for prices ,

Please Note :
Prices shown are not subject to the addition of vat ,

Extent of the Work

When entering into an agreement for electrical inspection and testing of a building under your control it is a fundamental requirement that the extent and limitations of the inspection and testing are fully described. It is recommended that the following be agreed prior to beginning the work, and we can assist you in determining your exact requirements for inspection and testing.
As it is neither practical nor possible to inspect all parts of an installation, we will agree a sampling process. This is normally in the order of 10%-20% of all accessories, fittings and control equipment.

For much of the testing the electrical system will be switched off. If this is a problem we can arrange the work at times when this is more convenient.
We will agree before commencing the work the amount of down time that can be tolerated and arrange a provisional program for switching off – totally, and individual areas or distribution boards if required.
Reports

On completion of the Inspection and Test a report will be provided, detailing the condition of the installation, results of all tests carried out, a list of any faults, and recommendations and a conclusion as to relative safety of the installation.

Insulation Resistance of the Electrical Installation ( 612.3 )

The purpose of these tests is to verify that:
i. there are no short circuits between current carrying conductors or between live conductors and earth.
ii. There is no reduction in insulation resistance due to damage or dampness.
Test Instrument:
An insulation resistance tester having a DC test voltage which depends upon the supply voltage (Table 61 ) is required.

The polarity tests are necessary to verify that: ( 612.6 )

i. All fuses, single pole switches and protective devices are connected to the phase conductor only.
ii. The Centre Contract of Screw Type Lamp holders is Connected to the Phase Conductor with Outer or Screwed Contacts Connected to the Neutral Conductor,
iii. Wiring is Correctly Connected in Socket Outlets and Similar Accessories.

RCD tests ( Max test current for 100mA RCD is 100mA ) 2392-10 : this will come up ←←←← -&-

Testing Methodology :
Inspection &Testing and Certification

Electrical Installation Certificate
The Regulations require that an Electrical Installation Certificate in the form set out in Appendix 6 together with Schedule of Test
Results shall be given to the person ordering the work :

Regulation : ( 632.4 )
Requires any defect or Omissions revealed by Inspector shall be made good before an Electrical Installation Certificate is issued ,

Regulation : ( 631.4 ) ( 632.3 )
Requires : the Electrical Installation Certificate shall be signed by a competent person or persons staring that to the best of their
Knowledge and belief the Installation has be designed , constructed , inspected and tested in accordance with BS-7671 and permissible deviations being listed ,

Note 1 :
Requires : the Electrical Installation Certificate may Require Three Signatures :
Multiple Signature Electrical Installation Certificate,
(1) The Designer ,
(2) Person Constructing the job
(3) Inspection & Testing Engineer ,
Note 2 :
An individual may sign all three parts if he/she has designed , constructed , inspected & tested installation ,
Note 4 :
Certificates :
Single Signature Electrical Installation Certificate,
Where design ,construction ,inspection and testing are the responsibility of one person, a Certificate with a single signature may replace the multiple signature form ,
Note 5 :
Electrical Installation Certificate will accompany the following :
(1) Schedule of Inspections :
(2) Schedule of Test Results : ( p-334 )

The Sequence of Tests : GN-3 ,
Initial Tests should be Carried out in the Following Sequence ,

(i) Before the supply is connected , or with supply disconnected as appropriate

(1) Continuity of Protective conductors , including main & Supplementary Equipotential bonding : ( 612.2.1 )
(2) Continuity of Ring Final Circuit Conductors : ( 612.2.2 )
(3) Insulation Résistance : ( 612.3 )
(4) Polarity ( 612.6 ) by Continuity Methods :
(5) Earth Electrode Résistance : ( Using Earth Electrode Résistance tester )

Initial Tests should be Carried out in the Following Sequence ,
(ii) With the Electrical Supply Connected re-check Polarity Using an Approved Voltage Indicator before Further Testing ( GS-38 )
(1) Earth Electrode Résistance, Using an Earth Fault Loop Impedance Tester (2) Earth Fault Loop Impedance : ↔ ( 612.9 ) Phase / Neutral – Impedance ,
(3) Prospective Fault Current ( 612.11 ) Additional Loop , Higher for Line / Neutral Test ,
(4) Additional Protection : ( 612.10 ) ↔ Testing Residual Current Operated Devices
(5) Functional Test : ( 612.13 ) ↔ of Switchgear and Control Gear

Note : All Test Results should be Recorded on a , Schedule of Test Results complete with Inspection & Test Result Schedules of Inspections must be provided to the person ordering the work ,

Continuity of Protective Conductors :
Continuity of protective conductors including main and supplementary bonding ( 612.2.1 )

Every protective conductor, including the earthing conductor, main and supplementary bonding conductors, should be tested to verify that the conductors are electrically sound and correctly connected.

Test method 1 detailed below, as well as checking the continuity of the protective conductor, also measures ( R1+R2 ) which, when added to the external impedance ( Ze ) enables the earth-fault loop impedance ( Zs ) to be checked.

Note : (R1+ R2) is the sum of the resistance of the phase conductor R1 and the circuit protective conductor R2 :

Instrument - Use a low-reading ohmmeter :

The resistance readings obtained include the resistance of the test leads. The resistance of the test leads should be measured and deducted from all resistance readings obtained unless the instrument can auto-null. ( Subtract )
Test method 1
Connect the phase conductor to the protective conductor at the distribution board or consumer unit so as to include all the circuit. Then test between phase and earth terminals at each outlet in the circuit. The measurement at the
circuit's extremity should be recorded on the schedule of test results and is the value of (R1 + R2) for the circuit under test.
The test should be carried out before connecting any exposed-conductive-parts, which may provide parallel paths to the protective conductors.

 

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Test method 2

Connect one terminal of the continuity tester to the installation main earthing terminal, and with a test lead from the other terminal make contact with the protective conductors at various points on the circuit, e.g. light fittings, switches, spur outlets etc. The resistance of the circuit protective conductors R2 is recorded on the test result schedule. Bonding conductor continuity can be checked using this test method. One end of the conductor and intermediate connections with services may need to be disconnected to avoid parallel paths.
Where ferrous enclosures have been used as the protective conductors, e.g. conduit, trunking, steel-wire armouring etc. the following procedure should be followed:

inspect the enclosure along its length for soundness of construction

perform the standard ohmmeter test using the appropriate test method described above.
Instrument - Use a low-reading ohmmeter for this test.

If the inspector feels that there may be grounds to question the soundness of this conductor, a further test may be performed using an a.c. ohmmeter which has a test voltage not exceeding 50 V and can provide a test current approaching 1.5 times the design current of the circuit excepting that it need not exceed 25 A.
Care needs to be taken when using high-current testers, as sparking can occur at a faulty joint. This test should not be carried out if this could be dangerous. Instrument - Use a high-current, low-impedance ohmmeter for this test.
( high current micro-ohmmeter suitable for measuring very low resistances )

TEST METHOD 1 - LINKING PHASE AND CPC :
Connect a temporary link between the phase conductor and the protective conductor at the distribution board. Using a low-reading ohmmeter test between the phase and earth terminals at each outlet in the circuit. The measurement obtained at the furthest point of the circuit should be recorded on the results schedule. This reading is the value of R1 + R2 for the circuit.

Note:
“ Main switch switched off “
Temporary link between Phase and CPC at the consumer unit. All fuses should be removed or MCB's switched off.

Remove temporary link when testing is complete.

TEST METHOD 2 - LONG LEAD METHOD

Connect one terminal of the ohmmeter to the earth terminal at the distribution board via a lead long enough to reach the furthest extremity of the circuit under test. The other terminal is then used to make contact with each outlet on the circuit.

Once resistance of the test leads is subtracted from the readings the corrected figure can be recorded.
Note:
All fuses out or MCB's switched off. Main switch switched off.

RING FINAL CONTINUITY TEST :
Purpose:

A test is required to verify the continuity of each conductor including the circuit protective conductor (CPC) of every ring final circuit.
The test results should establish that the ring is complete and has no interconnections.

Test Instrument required a Low Resistance Ohmmeter.

Step 1

Determine the resistance of each loop.

r1 - r2

r,n 1 – r,n 2

CPC1 - CPC2

Once the above readings have been established this will either confirm that the CSA of the CPC is the same as the phase conductor or smaller.

Step 2

Link-out Phase1 to Neutral 2 and Phase 2 to Neutral 1.
Now measure the resistance at every socket outlet between Phase and Neutral. The reading obtained should be the SAME at every socket outlet if the ring circuit has been connected up correctly.

The reading should be either ¼ of (Phase Loop + Neutral Loop) or ½ the reading of the Phase conductor loop.

Example

R1 - R2 = 1Ω

R,n 1 – R,n 2 = 1Ω

CPC1 - CPC2 = 1Ω

With Phase and Neutral cross linked, the reading at every socket outlet will be:

a) Phase loop 1 Ω + Neutral loop 1 Ω = 1 + 1 = 0.5 Ω
........................ 4 ............................ 4

b) Phase loop 1 Ω = 1 = 0.5 Ω ( 1÷ 2 = 0.5Ω )
....................2 ............. 2

Note: This reading is recorded on Test Certificate ,

Step 3

Remember

R1 = Resistance of Phase Conductor

R2 = Resistance of Circuit Protective Conductor

Now to measure R1 + R2 value of the ring final circuit.

Cross Link

Phase1 to CPC2

CPC1 to Phase2

Now measure the resistance at each socket outlet between Phase and CPC.

The reading at every socket outlet should be approximately the same.

Phase loop 1 Ω + Neutral loop 1 Ω = 1 + 1 = 0.5 Ω

....................4............................ 4 ( 1 +1 = 2 ÷ 4 = 0.5Ω


If one of the socket outlets is a spur, the reading here will be most likely the highest. It is this reading which needs to be recorded on the test result schedule under the column R1 + R2.

Note 1:
When carrying out this test you will automatically confirm the socket outlet, polarity, therefore there is no need to carry out a separate polarity test.
Note 2:
If the CPC cross sectional area is smaller e.g. 2.5/1.5, the resistance of the CPC will be 1.67 times higher than the phase resistance. Therefore, the readings measured at every socket outlet will differ slightly.

Note:

After connection of the supply, polarity should be confirmed using an approved voltage indicator (with leads conforming with HSE Guidance Note GS38).

Type of Inspection : 2392-10 most of them will come up Q/A ,

On demand Periodic Inspection and Test :
Periodic Inspection Report
Inspection Schedule & Schedule of Test Results

Documents :
Electricity at Work Regulations 1989
Health and Safety Executive Guidance Note GS38
BS7671 – Requirements for Electrical Installations

Personnel

First periodic test – designer / installer
Further periodic tests – Tester / Inspector
Extent & Limitations agreed with – person ordering the work

Instruments :
Continuity ring final circuit – low reading ohmmeter
Insulation resistance – insulation resistance tester
Live polarity – GS38 compliant voltmeter or test lamp.

Increase in Conductor Resistance :
Increase in ambient temperature
Increased circuit length - additions
Decreased conductor cross section – modifications

CPC Continuity :
At every Socket
Phase and CPC
Highest Value, therefore Circuit Value, for ( R1 + R2 )

Wiring systems not requiring separate CPC :
PVC-PVC insulated flat cable with CPC ( twin & earth )
MICC
SWA

Ring final circuit test :
P & N tested to ensure a valid ring circuit
If an interconnection existed

(i) CPC continuity, Figure-of-eight, (R1 + R2) measurement. Or
(ii) Polarity

Insulation Résistance, 600V Discharge lighting :
Insulation Résistance Tester
1000V d.c.
1.0 MΩ
Insulation Resistance 230V Installation :
500V
1.0 MΩ
2 MΩ
Polarity testing :
So that operating the device cuts line potential from the accessory protected.
Because live parts are only energised when lamp is in place.
To ensure supply is connected correctly at source.
Loop impedance :
Ze = External Loop Impedance
R2 = Resistance of circuit protective conductor
1.2 = Operating temperature correction factor. ( 1.2 is for bunched 70oC thermoplastic cables used at maximum operating temperature )
RCD tests : Loop impedance test determines that an earth fault loop path exists , Functional test determines that the RCD will actually operate in the event of a fault – electro-mechanical test using the ‘T’ button. , Max test current for 100mA RCD is 100mA

 

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Scenario :
Testing :
* Periodic Inspection and Test, plus an Initial Inspection and Test, for the new part of the installation . * Periodic Inspection Report , Electrical Installation Certificate, plus Schedules of Test Results and Schedules of Inspections , * The person ordering the work gets the originals * First periodic test determined either by statute or by the designer * Statutory document = Electricity at Work Regulations 1989 * Non-statutory = BS7671, HSE Guidance Note 38

Human senses :
* Sight , * Smell , * Hearing ,
* Limitations of the inspection should be agreed with the person ordering the work , * BS3036 Fuses will not carry the large fault current. (They have a safe breaking capacity of either 1 or 4 kA) * PSCC between phases can be taken as twice the maximum measured value between any phase and neutral.
* Although the circuit is single phase, 230V, discharge lamps generate much higher voltages when striking. Should the insulation resistance tests, therefore, be carried out at 1000V, with a minimum acceptable value of 1 M ohm ? Personally, I’d say, no – we’re testing the wiring and switchgear, but it’s a debatable point.

What is GS38 ? ( Test Lead ) 2392-10

Guidance Note GS38, published by the Health and Safety Executive (HSE), sets out in clear and concise terms the features that any instruments and meters should have if they are to be used to carry out electrical tests in accordance with BS 7671. In order to comply with the Electricity at Work Regulations 1989 it is critical that any competent person carries out electrical testing safely, and this guidance note draws attention to the risks of using test instruments that do not meet the GS38 standard. In brief, some of the requirements for test instruments include:
• The test probes should have finger guards, ideally 4mm or 2mm of exposed conductive tip (to prevent the user accidentally making contact with either the probes or live conductors under test) and should be fitted with a High Breaking Capacity inline fuse or fuse-and-resistor combination with a low current rating (to prevent the probes rupturing under high short-circuit currents and/or damaging the test instrument if incorrect range settings are used, typically drawing more than 500mA).

• The test leads should be adequately insulated to suit the environment in which they’re being used, are coloured differently from each other so as to be distinguishable, are flexible, are capable of handling the maximum current range of the test instrument and are shrouded or sheathed to protect against mechanical damage, securely connect the leads to the test instrument and safeguard against the possibility of direct contact with live parts.

 

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Question 1 :
State the necessary action that should betaken by an inspector on discovering a damaged socket outlet with exposed live parts
during a periodic inspection and test :
GN3 Page 14 - 1.2 ( Required Competence ) ( 634.2 )
(1) Make an immediate recommendation to the client to isolate the defective part :
Question 2 :
State the documentation that should accompany an Installation Certificate or Periodic Inspection Report ,
GN3 Page 14 - 1.3.1 ( Certificates and Reports ) ( 631.1 : 632.1 )
(1) Electrical Installation Certificate , together with a Schedule of Inspections
(2) and a Schedule of Test Results ,
Question 3 :
Why is it necessary to undertake an Initial Verification ?
GN3 Page 17 - 2.1 ( Initial Verification ) ( 610.1 : 611.2 : 612.1 )
(1) Confirm that installation complies with designers intentions ,
(2) Inspected and Tested Constructed, in accordance with BS 7671 ,
Question 4 :
State the requirements of Chapter 61 of BS 7671 with regard to initial verification ,
GN3 Page 17 - 2.1 ( Initial Verification ) ( 611.2 )
(1) All fixed equipment and material complies with applicable British Standards or acceptable equivalents ,
(2) All parts of the fixed installation are correctly selected and erected ,
(3) No part of the fixed Installation is visibly damaged or otherwise defective ,
Question 5 :
Identify four Non-Statutory documents that a person undertaking an inspection and test need to refer to ,
General Knowledge
BS 7671
IEE On-Site Guide
Guidance Note 3 Guidance Note : GS 38 , ( HSE )
Question 6 : Which non-statutory document recommends records of all maintenance including test results be kept throughout the life of an installation ? GN3 Page 17 - 2.1 (Initial Verification )( 631.1 )
The Memorandum of Guidance on The Electricity at Work Regulations 1989 ( HSR25 ) (EAWR Regulation 4(2)
Question 7 :
Appendix 6 of BS 7671 allows the use of three forms for the initial certification of a new installation or for an alteration or an addition to an existing installation. State the title given each of these certificates ,
GN3 Page 18 - 2.2 ( Initial Verification )
(1a) Multiple signature Electrical Installation Certificate ,
(2a) Single signature Electrical Installation Certificate ,
(3a) Minor Electrical Installation Works Certificate ,
(1b) The Multiple signature certificate allows different persons to sign for design , construction , inspection & testing,
And allows two signatories for design where there is mutual responsibility . where designers are responsible for identifiably separate parts of an installation , the use of separate forms would be appropriate .
(2b)where design , construction , inspection and testing are the responsibility of one person, a certificate with
A single signature may replace the multiple signature form ,
(3b)This Certificate is to be used only for minor works that do not include the provision of a new circuit ,
Such as an additional socket-outlet or lighting point ton an existing circuit ,
Electrical Installation Certificate , 2392-10 :
to be used when One person is responsible for the design Construction , inspection & testing of an Installation , p-332 ,
Approved Contractor issuing the Certificate has not been responsible for the design / or the inspection & testing of the
Electrical work ( p-333 certification of the three elements must be carried out separately using , ↔ the three sections headed ↔ Designer ( no 1 ) .. ↔ Designer ( no 2 ) .. first periodic (T)-(1) Designer / Installer , further periodic (T)-(2)
Tester / Inspecter , ( Construction (No 2) : Inspector ( Inspection / Testing ( No 3 )
Question 8 :
Under what circumstances would it be appropriate to issue a single signature Electrical Installation Certificate ?
GN3 Page 18 - 2.2 ( Certificates )
Where design, construction inspection and testing is the responsibility of one person ,
(2b)where design , construction , inspection and testing are the responsibility of one person, a certificate with
A single signature may replace the multiple signature form ,
Question 9 :
State the information that should be made available to the inspector ,
GN3 Page 18 - 2.3 ( Required information )
(1) Maximum demand , expressed in amperes , kW or kVA per Phase ( After diversity is taken into account )
(2) the Number and type of live conductors of the source(s)of energy and of the circuits used in the installation ,
(3)Type of earthing arrangements, used by the installation and any facilities provided by the distributor for the user ,
(4)the Nominal voltage(s) and its characteristics including harmonic distortion ( 313.1 ),
(5) the nature of the load current and supply frequency , (6) the prospective fault current at the origin of the installation , ( PFC ) (7)The Earth Fault Loop Impedance ( Ze ) of that part of the system external to the installation , (8) The suitability for the requirements of the installation, including the maximum demand , (9) Type and rating of overcurrent protective device acting at the origin ,of the installation ,
Note : These characteristics should also be available for safety services such as ( UPS ) and Generators ,

Question 6 : ops Which statutory document recommends records of all maintenance including test results be kept throughout the life of an installation ? GN3 Page 17 - 2.1 (Initial Verification )( 631.1 )
The Memorandum of Guidance on The Electricity at Work Regulations 1989 ( HSR25 ) (EAWR Regulation 4(2)

 

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Inspection , Testing , Certification & Reporting :

Testing Continuity of Protective Conductor at a Lighting Switch by Wander Lead Method ,
Instrument : set on Ohms “ Continuity ↔ 20Ω ( Dead Test )

One Lead on Earthing Terminal at CCU / One Lead on the Earthing Screw on the Back-Box : you have Continuity = 0.41Ω

The Wander Lead Method , ( R2 )
This method is used principally for testing protective conductors that are connected to the main earthing terminal ( Main Equipotential bonding conductors , Circuit Protective Conductors and so on ) The correct Polarity of circuit connections will need to be Verified separately ,

Where a continuity test involves the opening of enclosures etc. that part of the installation will need to be isolated ,
One terminal of the continuity test instrument ids connected to the main earthing terminal with a long lead ( or “ wander Lead “ ) and ,
With a lead from the other terminal, contact is made with the protective conductor at every position to which it is connected in that circuit ,
Such as at socket-outlets, lighting points, fixed equipment points, switches, exposed-conductive-parts and extraneous- conductive-parts,
By this means, provided that no parallel paths are present, the continuity of the protective conductor back to the main earthing terminal can be verified , and its Résistance measured ,

A main or supplementary bonding conductor can be tested by simply attaching the leads of the test instrument to each end of the conductor, having temporarily disconnected one end of that conductor to remove parallel paths ,

Continuity testing of a Ferrous Enclosure using the wander lead method ,

Where a Ferrous Enclosure , such as Steel Conduit or Steel Trunking is used as a Circuit Protective Conductor,
The Integrity of the Enclosure should be verified for compliance with BS-7671, where reasonably practicable by Inspection & Testing

Inspection is to confirm the soundness of the enclosures conductive path , the inspector should indentify any deterioration such as excessive corrosion or the ability of any joints to provide durable Electrical Continuity and Adequate Mechanical Strength ,

Where Safe to do so, Testing of the Conduit or Trunking can be carried out by the Measurement of ( R1+ R2 ) or the Wander Lead method ,
Although these are ( Dead Tests ) both of these test procedures may require access to enclosures containing live parts ,
Therefore → ( Safe Isolation Must be Carried Out ) ← prior to gaining access , to prevent contact with any live parts ,
→ ( Before carrying out the Continuity test, “ Check that “ :

* Access to the Equipment is Not-Restricted , and once the Consumer Unit Cover is Removed , “ Check that “ :
* The basic Protection inside the Consumer Unit meets or exceeds the Requirements of IP2X or IPXXB , and
* The Terminal Insulated covers are unlikely to be Accidentally Displaced during Testing ,

The Wander Lead Method for Obtaining ( R2 ) values has been Described ,

Instrument : set on Ohms “ Continuity ↔ 20Ω ( Dead Test )

One Lead on the Earthing Screw on the Metal Back-Box : you have Continuity = 0.41Ω
The Other Lead on the Earthing Screw on the Metal Back-Box : ( your working on box –to-box : back to CCU Earthing Terminal , ( R2 )

( R1 + R2 )

For a simple circuit R1 + R2 is the phase conductor + the CPC impedance values and will be in ohms subtract from this any value for the leads that were obtained on the instrument check. The neutral should have the same csa of the phase conductor and should be almost equal to that of the phase impedance depending upon the circuit arrangement. For a three phase circuit the highest impedance is the one that could prevent a protective device operating thus this is the one used in practice against the chart to determine whether or not the reading is low enough and therefore recorded. Polarity can be checked at this point by making sure that single pole switches break the phase conductor and not the neutral or CPC.
Once continuity of all possible circuit combinations have been recorded I would guess that each circuit is tested for insulation resistance using the 500V range of an insulation tester for domestic premises. Although the leads should be shorted together to verify the meter reads zero, I prefer to place one lead on an earth and then verify my contact by connecting the other lead to another earth location close by. Since all wiring would need to be tested it is important to have all the switches are turned on. Where there is two lighting circuits this means that all combinations of the switching needs to be verified. I doubt the exam would go beyond the simple two way circuit.
A reading of zero Megohms could indicate that a shorting wire is still in place or that there is a fault. If a low test is obtained between phase and neutral it could be that a neon is used on a fused spur or that a genuine fault is present.

If tests revealed a fault and I resolved the problem then I would begin the tests again in case during my investigations I had inadvertently disturbed the wiring.

Electrical Inspection Testing & Certification : ( Dead Tests ) df

Electrical Installation Certificate
The Regulations require that an Electrical Installation Certificate in the form set out in Appendix 6 of BS7671 together with a schedule of test results shall be given to the person ordering the work.

Regulation ( 632.4 )
Requires any defect or omissions revealed by the inspector shall be made good before an Electrical Installation Certificate is issued.

Regulation ( 631.4 )
Requires: the Electrical Installation Certificate shall be signed by a competent person or persons stating that to the best of their knowledge and belief the installation has been designed, constructed, inspected and tested in accordance with BS7671 and permissible deviations being listed.

Note 1:
An Electrical Installation Certificate may require three signatures :
(1) The designer :
(2) Person Constructing the Job :
(3) Inspection and Testing engineer.
Note 2:
An individual may sign all three parts if he/she has designed, constructed, inspected and tested the installation.
Note 3:
The Electrical Installation Certificate will accompany the following :
(1) Schedule of Inspections : 2391-10 ↔ Use the Right Wording ← on your Exam
(2) Schedule of Test Result : 2391-10 ↔ Testing Checklist ( 611.3 ) ←←←
“ Test Result Schedule “ “ Inspection Schedule “

The Sequence of Tests :

Initial tests should be carried out in the following sequence:
Before the supply is connected, or with supply disconnected as appropriate
GN-3 ( 612.2.1 ) continuity of protective conductors, including main and supplementary bonding
GN-3 ( 612.2.2 ) continuity of ring final circuit conductors ( R1 + R2 )
GN-3 ( 612.3 ) insulation resistance ( “ High Résistance Using d.c. Voltage )
GN-3 ( 612.6 ) polarity ( by continuity methods )
GN-3 ( 612.7 ) earth electrode resistance, using earth electrode resistance tester ( Method 1 )

With the electrical supply connected re-check polarity using an approved voltage indicator before further testing : ≈ ≈ ≈ ≈

GN-3 ( 612.9 ) earth electrode resistance, using an earth fault loop impedance tester ( Method 2 )
GN-3 ( 612.9 ) earth fault loop impedance : ( Phase / Neutral = Impedance ) where protective measures are used which require a knowledge of ( earth fault loop impedance ) the relevant impedances shall be measured ,or determined by an alternative method , Zs = Ze ( R1 + R2 ) :
Note : further information on measurement of earth fault loop impedance can be found in appendix 14 / p-361
Zs (m) ≤ 0.8 x Uo ÷ Ia : ( 230 ÷ 24A = 9.58 , ( Ze / 0.8 x Zs 9.58 = 7.66
From the City & Guild Chief examiners reports it appears that many get calculations of ( Zs ) ( Ze ) R1 and R2 wrong.
( Zs ) is the sum of ( Ze ) R1 and R2 seems simple enough. Zs = Ze + ( R1+R2 ).
( Ze ) is the external impedance. Although you can calculate the value, it is more normal that the value is obtained by measurement using a suitable instrument or by enquiry.
R1 is the resistance of the phase conductor :
R2 is the resistance of the CPC or circuit protective conductor. :
In practical test situations the value of R1 + R2 is obtained in one test so could in effect be considered as one value say Rt. So the equation would become Zs = Ze + Rt.
So why Z and R ? :
Z is the impedance and applies to AC circuits :
R is resistance and applies to DC circuits :
GN-3 ( 612.11 ) prospective fault current ( Live / Neutral )
GN-3 ( 612.10 ) residual current operated devices ( BS – Only - 200mS ( BS-EN – 300mS :
GN-3 ( 612.13 ) functional test ( Light Switches , switchgear and control gear
Note:
All test results should be recorded on a schedule of Test Results form
Report Forms complete with Schedules of Inspection and Schedules Test Result must be provided to the person ordering the work.

 

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TT , TN-C-S , IT , TN-C Earthing Arrangements :
In Latin earth is called Terra (Terre in French ) so we get Terra Firma, on solid ground.

So the first letter denotes if the supply is connected to Earth or Terra with the capital letter T. If insulated from earth then I is used, I for insulated.

The second letter denotes where the consumers earth is connected to. So T would indicate to earth. So TT means that the supply transformer star point is connected to earth and the consumers equipment is also connected to earth using earth spikes etc.

In an IT system the supply transformer has no connection to earth but the consumers equipment is connected to earth using earthing spikes etc.

N stands for neutral and thus in a TN system the consumers earth is connected to earth via the neutral of the supply.
TN S is where the earth and neutral are fed back to the supplier with separate conductors.
TN C is where the earth and neutral are fed back to the supplier using one conductor. ( PEN )
TN-C-S is where the earth and neutral are fed back to the supplier using one conductor but this time the connection of the earth to the neutral is not directly made at the consumers end thus there are two separate conductors from the premises.

Testing – ( the live tests )
612.8 - Protection by automatic disconnection of supply
612.9 - Earth fault loop impedance
612.10 - Additional protection ( RCDs )
612.11 - Prospective fault current
612.12 - Check of phase sequence
612.13 - Functional testing ( inc. RCDs )
612.14 - Verification of voltage drop
Testing – ( the dead tests ) GN-3
612.2 - continuity of protective conductor’s including main and equipotential bonding
612.2.2 - Continuity of ring final circuits
612.3 - insulation resistance (see table 61)
612.4 - protection by SELV, PELV or protection by separation
612.5 - Insulation resistance of floors and walls
612.6 - Polarity
612.7 – Earth electrode resistance
Testing – ( the dead tests ) GN-3
Table 61 – Minimum Values of Insulation Resistance
Note: some of these values have changed from the previous edition
≥ 1.0 1000 Above 500V ≥ 1.0 500 Up to and including 500V with the exception of the above system ≥ 0.5 250 SELV and PELV Minimum insulation resistance ( M Ω ) Test voltage d.c. ( V ) Circuit nominal voltage ( V )

The correct documentation must be issued to the person ordering the work TYPE OF WORK COMPLETED TYPE OF FORM REQUIRED New installation or change to existing installation Electrical Installation Certificate New installation work that does not include the provision of a new circuit Electrical Installation Certificate or Minor Electrical Installation Works Certificate Alterations or additions Electrical Installation Certificate Alterations or additions that does not include the provision of a new circuit Electrical Installation Certificate or Minor Electrical Installation Works Certificate Periodic Inspection and Testing Periodic Inspection Report

* Electrical Installation Certificate : This form to be used when only one person is responsible for the design, construction and testing of the installation * Electrical Installation Certificate : This requires 3 signatures ( The designer , The constructer , The inspector )
You will need to complete one of these for every installation that has been tested.
The Installation Test Certificate : Minor Works Certificate To be used for minor works only, Not for new circuits, or New installations

Periodic Inspection Report : To be used when “next inspection” date is due – or On change of use - or On change of ownership This is now part of the “sellers pack” when homes are for sale
SPECIAL INSTALLATIONS OR LOCATONS ;
COMPETANT PERSON , From Part 2 Definitions , A person who possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and is at all times able to prevent danger and, when appropriate, injury to himself/herself and others.
Check of phase sequence For multi-phase circuits there is a requirement to verify that phase sequence is maintained
Verification of voltage drop This subject matter was covered previously in Section 523 ( and Appendix 12 ). Regulation 612.14 is short , so briefly familiarize yourself with its content.
Part 6 Inspecting and Testing :
Limited changes in Part 6 with model certificates & reports remaining largely unchanged
Insulation values increased - For systems up to and including 500 V the minimum insulation resistance is now 1MΩ
More detailed requirements are provided in relation to RCD testing
New regulations are included in relation to the checking of phase sequence and verification of voltage drops
Section 610 – General : 610.1

Every installation shall, during its erection and on completion before being put into service, be inspected and tested to verify, as far as is reasonably practicable, that the requirements of the regulations have been met.
Precautions shall be taken to avoid danger to persons and to avoid damage to property and installed equipment.
Section 610 – General
610.2 – See sections 131, 311 to 313 and 514.9.1 for information required for the fundamental principles.
610.3 – The verification shall include comparison of the results with the relevant criteria to confirm that the requirements of the “Regs” have been met.
610.4 – For an addition or alteration to an existing installation. It shall be verified that the addition or alteration complies with the regulations, and does not impair the safety of the existing installation.
Section 610 – General (cont.)
610.5 – The verification shall be made by a competent person .
610.6 – On completion of the verification, according to regulations 610.1 to 610.5, a certificate or certificates, shall be prepared.
Section 611 – Inspection
611.1 – The inspection shall precede testing and shall normally done with that part of the installation under inspection disconnected from the supply.
Section 611 – Inspection (cont)
611.2 – The inspection shall be made to verify that the installed electrical equipment is:-

1.
In compliance with section 511 (this may be ascertained by mark or by certification furnished by the installer or by the manufacturer), and
Correctly selected and erected in accordance with the regulations, and
Not visibly damaged or defective, so as to impair safety.
Section 611 – Inspection
611.3 – the inspection shall include at least the checking of the items on the inspection check list, where relevant to the installation, and where necessary, during erection:
A complete inspection checklist is shown in appendix 6 and also available to download from Forms for electrical contractors - The IET as indeed, are all of the forms that you may require.
2.
Section 611 – Inspection
The Schedule of Inspection
This form will be used for ALL installations
Record all your observations here with either a tick ( ) a cross ( x )or ( N/A ) or ( Lim ) p- 340 / regs
Simply work your way through the form item by item, this will ensure compliance with regulation 611.3.
612 - Testing
The tests of regulation 612.2 to 612.13, where relevant, shall be carried out and the results compared with the relevant criteria.
The tests of regulation 612.2 to 612.6, where relevant shall be carried out in that order before the installation is energized .
Where the installation incorporates an earth electrode, the test of regulation 612.7 shall also be carried out before the installation is energized
612 – Testing
If any test indicates a failure to comply, that test, and any preceding tests, the results of which may have been influenced by the fault indicated, shall be repeated after the fault has been rectified.
Some methods of test are described in the IEE Guidance Note 3 ( when available ), Inspection and Testing, published by the Institute of Engineering and Technology.
Other methods are not precluded provided that they give valid results.
612 – Testing Section 612 details the required tests to be for initial verification. The tests should be carried out in a prescribed sequence, some prior to the circuits being energized.

( 314.1 ) dividing the installation into circuits so as to: -
Avoid danger and minimize inconvenience in the event of a fault
Facilitate safe testing, inspecting and maintenance
( 314.2 ) ( 314.3 ) ( 314.4 )

 

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17th Edition requirements for testing of RCDs The 17th Edition has the following requirements in terms of verification of installed RCDs:

612.8.1 requires the effectiveness of automatic disconnection of supply by RCD to be verified using test equipment meeting the requirements of BS EN 61557-6 ( Electrical safety in low voltage distribution systems up to 1000 V a.c. and 1500 V d.c P-12 Regs ).
– Equipment for testing, measuring or monitoring of protective measures. Residual current devices (RCD) in TT, TN and IT systems). This is to confirm that the relevant requirements of Chapter 41 (Protection against electric shock) are met.

BS EN 61557-6 has requirements for the following tests to be applied to RCDs:
- Non-tripping (50%) test
- Tripping (100%) test
- 5 I∆n ) (500%) test

612.13.1 requires the effectiveness of the integral test facility of an RCD to be verified.
415.1.1 states that where an RCD having an I∆n of 30 mA or less is installed to provide additional protection, its operating time should not exceed 40 ms at a residual current of 5 I∆n .

Recommended test procedures
Although the following tests are not required by BS 7671: 2008 they are a method of establishing that the
device meets the requirements of Chapter 41. Remember, in order for reliable results to be obtained
when performing these tests, any loads should be disconnected from the circuits and/or outlets under test .

Non-tripping test.
The purpose of this test is to confirm that an RCD of any type or trip rating is not overly sensitive and is a measure
intended to enable unsuitable RCDs to be identified and removed from service. The continued presence of overly sensitive RCDs tends to reduce user confidence in such devices and may encourage the adoption of potentially dangerous practices such as the “bridging-out” of RCDs in order to avoid unwanted tripping.

Test procedure - With a leakage current equal to 50% of the rated residual operating current (I∆n ) ( applied, the RCD should not operate.
Tripping current test
The purpose of this test is to confirm that the residual operating current of the protective device is less than or equal to the rated
residual operating current. This is a measure of the continued effectiveness of the device to work as required by
BS 7671 and in accordance with its product specification when installed for the purpose of providing automatic
disconnection in the event of a fault. It does not demonstrate its suitability in terms of providing additional
protection. The test should be performed in both the positive and negative half-cycles.

Test procedure -

General purpose RCD to BS EN61008 and RCBO to BS EN 61009
With a leakage current flowing equivalent to 100% of the rated residual operating current (I∆n ) of the RCD, operation should occur within 300 mS.

“S” type RCD to BS EN 61008 ( incorporating an intentional time delay )
With a leakage current flowing equivalent to 100% of the rated residual operating current ( I∆n ) of the RCD, operation should occur
within a time range from 130 mS to 500 mS.

General purpose RCD to BS 4293 and RCD protected socket-outlets to BS 7288 With a leakage current flowing equivalent to 100% of the rated residual operating current ( I∆n ) of the RCD, operation should occur within 200 mS.

General purpose RCD to BS 4293 incorporating an intentional time delay With a leakage current flowing
equivalent to 100% of the rated residual operating current ( I∆n ) of the RCD, operation should occur within a time range from 50% of
the rated time delay plus 200 ms to 100% of the rated time delay plus 200 ms.

Test to confirm suitability for use to provide additional protection :

The purpose of this test is to confirm the continued suitability of an RCD having a rated residual operating current ( I∆n ) not exceeding 30 mA to
provide additional protection under no-fault conditions ( in the 16th Edition, this was known as supplementary protection against direct contact ).
The test should be performed in both the positive and negative half-cycles.

Test procedure -
With a leakage current flowing equivalent to 500% of ( i.e. 5 times ) the rated residual operating current ( I∆n) of the RCD,
operation should occur within 40 ms.

Confirmation of the effectiveness of the integral test facility :

RCDs have an integral test device to simulate the passing through the detecting device of a residual current. This makes possible periodic testing of the ability of the residual current device to operate. However, it should be remembered
that operation of the integral test button merely confirms the continuing functioning of the electrical and mechanical components of the
RCD. It does not confirm that the device is capable of operating in accordance with the specification of the relevant product standard
or, indeed the requirements of the requirements of BS 7671.

Test procedure - With the supply to the RCD switched on and with the RCD in the “on” position, the button
marked “T” or “Test” on the RCD is pressed. The RCD should switch off. ( 514.12.2 ) recommends that the integral test button of an RCD
is pressed quarterly ( every 3 months ).

Summary :
RCDs should be tested at 50% , 100% and, if providing additional protection 500% of their rated residual operating current ( I∆n ) . In addition, the integral test device should be operated quarterly. Where an RCD is employed to achieve the disconnection time
required by Table 41.1 it is necessary to confirm that the maximum earth fault loop impedances (Zs) stated for a particular sensitivity of RCD in Table 41.5 are not exceeded in the circuit to which they provide protection. More in depth descriptions of both
RCD and earth fault loop impedance testing procedures are given in IEE Guidance Note 3 Inspection and testing

 

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17th EDITION REQUIREMENTS FOR THE TESTING OF RCDs :

The 17th Edition of the Wiring Regulations (BS 7671: 2008) will introduce a number of new requirements for the installation of
RCDs, therefore it is timely to look at the requirements within the17th Edition for verification of RCDs. The continuing effectiveness of these RCDs needs to be confirmed periodically. This article discusses the verification required where RCDs are
used to provide automatic disconnection of supply in the event of a fault and additional protection. It should be stated at this point that the 17th Edition does not introduce any significant changes in the requirements for the testing of RCDs even where they are installed to provide automatic disconnection in the event of a fault ,

Use of RCDs to achieve automatic disconnection in case of a fault :
411.3.2.1 requires (in most cases) that a protective device shall interrupt the supply to a line conductor of a circuit or equipment in the event of a fault of negligible impedance between said line conductor and an exposed conductive- part or a protective
conductor for the circuit or equipment within the appropriate required disconnection time. A disconnection time of 5 seconds
for distribution equipment and final circuits of rating exceeding 32A is permitted by 411.3.2.3. Similarly, a disconnection time of 1 second for distribution equipment and final circuits of rating exceeding 32 A is permitted by 411.3.2.4. : 411.3.2.2 states that the maximum disconnection times of Table 41.1 shall be applied to final circuits not exceeding 32 A. Table 41.1 gives the maximum
disconnection times for final circuits not exceeding 32 A of varying nominal voltages forming part of an
installation having either TN or TT system earthing. These disconnection times may be met by the use of fuses, circuit breakers (formerly known as MCBs) or RCDs. is used to meet the requirements of 411.3.2.2, that is, to provide the required disconnection time, the maximum values of earth fault loop impedance in Table 41.5 may be applied. The maximum permissible earth
fault loop impedances (Zs) to ensure RCD operation for non-time delayed RCDs protecting final circuits not
exceeding 32 A are given in Table 41.5, a new table introduced in the 17th Edition, which is reproduced below.
Where an RCD is employed to achieve the disconnection time required by Table 41.1, it is necessary to satisfy
ourselves that the maximum earth fault loop impedance (Zs) stated for a particular sensitivity of RCD in Table 41.5 is not exceeded in the circuit to which they provide protection. This is in effect the same procedure that we applied in earlier editions where fuses
or circuit breakers were used to achieve the necessary disconnection time and indeed continue to apply for fuses and circuit breakers in the 17th Edition. Regardless of which type of protective device is used to achieve the disconnection times required by Table
41.1, whether fuse, circuit breaker or RCD, there is no requirement to confirm that the required disconnection time can be achieved by testing the protective device. Rather, we confirm that the earth fault loop impedance of the protected circuit does not exceed the relevant tabulated maximum earth fault loop impedance for the type / sensitivity of the protective device intended to provide
the required disconnection time.

Maximum earth fault loop impedance (Zs) to ensure RCD operation in accordance with Regulation 411.5.3 for non-delayed RCDs to BS EN 61008-1 and BS EN 61009-1 for final circuits not exceeding 32 A

( 411.3.2.2 ) 230v
TN- Systems : The maximum disconnection time stated in table 41.1 shall be applied to final circuits Not-Exceeding 32Amp
( 411.3.2.3 )
TN- Systems : in a TN-system, a disconnection time Not exceeding 5sec is permitted for a distribution circuit and for a circuit Not covered by Regulation 411.3.2.2 ,
( the table you require TT-systems 41.5 p-50

Resistivity :

Double cable length – Double Conductor Resistance to 1.6 Ω, but halve insulation resistance to 50 MΩ
Halve . CSA – double conductor resistance to 1.6 MΩ, but insulation resistance is unaffected and remains 100 MΩ

Resistivity :
A twin cable has a Phase to Neutral résistance value of 100MΩ and an individual conductor résistance values of ( 0.8Ω )
Determine the values if the cable ….
(a) was double in length ,
(b) length as the same but the conductor cross-section areas was halved ,
Conductor Résistance
This is a function of the resistivity of the conductor material :
In other words , résistance is directly proportional to length and inversely proportional to area ,
So doubling length or halving the area will both double résistance , try it with some values ,

Let’s say the original length is 40m and the area is 2mm2 . The equation then , is :
0.8 = p x 40 ÷ 2 ( 0.8 x 2 ÷ 40 = 0.04 ( ignoring the units )
Double length : R = 0.04 x 80 ÷ 2 = 1.6Ω : / Halve area : R = 0.04 x 40 ÷ 1 = 1.6Ω
Beware the question that asks what happens if the diameter is varied , because is proportional to the diameter squared ,
Doubling diameter will increase the area by four times; halving the diameter will quarter the area ,
Insulation Résistance :
The Insulation between two conductors is considered to act as a ( Series of many high résistance in parallel )
Résistance ( because of the greater number of apparent parallel paths ) Taking the insulation résistance of the original length as R1 ,
Adding an identical extra length is like adding a second R1 in parallel , So :

…….... 1 ……..... 1
….. ─── = ─── so R1 = Rtotal = 100MΩ ( in the first instance )
……....Rtotal … R1

………………………. ……......... 1 ……..... 1……...... 1……...... 2
With double the length ….. ─── = ─── + ─── = ─── so new Rtotal = 50MΩ
…………………………......... Rtotal …... 100 ….... 100…...... 100

Changing the conductor CSA , should have no effect on the insulation résistance for the same value of voltage applied ,

Insulation Resistance Values
0.00 MΩ = dead short :
0.08 MΩ = low insulation resistance fault :
>200 MΩ = healthy circuit :

Notes: ensure all neon's are removed or isolated before commencing testing, as these will make test results appear low during insulation resistance testing.

Notes: Neon's will cause false readings, as will emergency or discharge lighting, so ensure these are all disconnected prior to commencing tests.

Prospective short circuit current (PSC) testing

The prospective short circuit or fault current at any point in an electrical installation is the current that would flow in the circuit if no circuit protection operated and a complete (very low impedance) short circuit occurred. The value of this fault current is determined by the supply voltage and the impedance of the path taken by the fault current. Measurement of PSC can be used to check that protective devices within the system will operate within safety limits and as per the safe design of the installation. PSC is normally measured between the phase and neutral at the DB or at a socket outlet.

 

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The 17th Edition of the IEE Wiring Regulations (BS 7671:2008) places much greater emphasis on the use of RCDs.
It is well-known that most circuits feeding 13A socket-outlets now require RCD protection but equally important are requirements for additional protection of wiring concealed in walls or partitions, which includes lighting circuits and their concealed switch wiring. This means that the vast majority of domestic circuits, power and lighting now require 30mA RCD protection :
There are also important requirements to minimise nuisance tripping and collateral risks due to a tripped RCD affecting other circuits, such as lighting.

Socket-outlets :
Rule 411.3.3 calls for additional protection by means of a 30mA RCD for all socket-outlets with a rated current not exceeding 20A for use by “ordinary persons”. The only exceptions allowed are for socket-outlets for use under the supervision of skilled or instructed persons (e.g. some commercial/industrial locations) or a specifically labelled socket provided for connection of a particular item of equipment (such as a freezer). :
This rule clearly covers the vast majority of domestic circuits feeding 13A socket-outlets, and any other socket-outlets (5A, 15A etc.) up to 20A. There is also a requirement for RCD protection of circuits feeding mobile equipment with a current rating up to 32A for use outdoors. :

Cables in walls or partitions
Rule 522.6.7 calls for RCD protection of wiring concealed in walls or partitions. All concealed wiring at a depth of less than 50mm now requires protection by a 30mA RCD unless it is provided with earthed mechanical protection, for example by metallic conduit or trunking. This applies to many lighting circuits and their switch wiring, including those installed in previously defined a “Safe Zones”. :

There is a further requirement for protection by means of a 30mA RCD where cables are concealed in walls constructed with metal stud partitions, irrespective of the depth from the surface, unless provided with protection in the form of earthed metallic covering, trunking, conduit or other mechanical protection so as to avoid damage to the cable during installation or construction of the wall. :
Special locations :

Rule 710.411.3.3 calls for RCD protection of all circuits in specific locations such as those containing a fixed bath or shower. This means that, in bathrooms or bedrooms with en-suite facilities, circuits feeding lighting, heating and showers must have RCD protection. :
Other “special installations and locations” as defined in Part 7 of the Regulations are also required to have RCD protection. These include swimming pools and saunas, agricultural premises, caravans and caravan sites, floor and ceiling heating systems. :

Sub-division of circuits :
Rules 314.1 and 2 require that every installation should be divided into circuits as necessary to avoid danger and minimise inconvenience in the event of a fault. Designers are required to reduce the possibility of unwanted RCD tripping due to excessive protective conductor currents but not due to an earth fault. :
Separate circuits may be required for parts of the installation which need to be separately controlled in such a way that they are not affected by the failure of other circuits. The appropriate subdivision should take account of any danger arising from the failure of a single circuit, for example an RCD trip causing the disconnection of an important lighting circuit. :

This affects the configuration of the protective devices in a consumer unit. For example if a number of circuits are protected by a common 30mA RCD, lighting circuits need to be spread over more than one RCD. :
Rules 314.1 & 2 also call upon the designer to take steps to reduce the likelihood of unwanted RCD tripping due to excessive protective conductor currents, other than earth faults. :
Typical situations would include IT equipment with certain types of radio frequency interference suppression, and certain types of heating equipment. The cumulative effect of such loads can produce a standing earth leakage current that is beyond the threshold point of a normal 30mA RCD. However this situation is becoming more common in residential environments. :

Earth loop impedance ( 2392-10 )
It should also be noted that Chapter 41 of the Regulations includes revised earth loop impedance tables based on a nominal voltage of 230V (Previously 240V). This results in slightly lower values of earth loop impedance and could, in some situations, mean that RCDs will be required to achieve the required disconnection time where previously overcurrent protection devices would be considered adequate. :

17th Edition IEE Wiring Regulations :

Key Changes : RCD Protection to Socket Outlets ,

• Socket outlets rated not exceeding 20 A and intended for general use by ordinary persons must be protected with 30 mA RCDs(Residual Current Devices). This means that general purpose sockets in domestic and similar properties must have RCD protection. An exception can be made for socket outlets for specific purposes e.g. domestic freezer circuit, this socket should be suitably labelled or otherwise identified.
• External sockets rated not exceeding 32 A must also have 30 mA RCD protection.
Installation of cables – RCD Protection Requirements :
• Cables that are buried less than 50mm into a wall or partition and are not enclosed in earthed metallic covering or have mechanical protection capable of resisting nails or screws should be protected by a 30 mA RCD as well as being installed in the ‘safe zones’ as previously permitted.
• Similarly, irrespective of depth of cable, cables that are installed in metal framed walls require 30 mA RCD protection if not otherwise protected by earthed metallic covering. :

The above requirements do not apply to installations where the installation is intended to be under the supervision of a skilled or instructed person, such as in office buildings, large retail outlets and industrial premises. :

Bath/ Shower Rooms (containing a fixed bath or shower) :
• All circuits within a bathroom must have RCD (30mA) protection. Where this is provided and main equipotential bonding is used in the installation then supplementary equipotential bonding is not required.
• Bathrooms being modified or refurbished can either have their supplementary equipotential bonding extended or can be rewired with the installation of RCDs.
• Zone 3 has been removed
• 13A sockets in bathrooms are allowed providing they are installed at least 3m from the edge of the bath and protected by a 30mA RCD.
Under Floor Heating Systems :
Underfloor and ceiling heating systems are now covered as a special location/installation.
• A plan of the heating system shall be provided for each system (showing location, area, rating details, descriptions for use etc). A copy of the instructions for use should be fixed adjacent to the distribution board supplying the heating.
• Heating systems which do not have an exposed conductive covering or mesh must have installed on site a suitable exposed conductive part installed above the heating element . This could be in the form of an earthed metallic grid with spacing of not more than 30mm.
• A 30mA RCD must be used as the disconnection device.
• Heating systems of Class II (Double insulated) construction shall be provided with 30mA RCD protection.
•Floor heating systems in bathrooms the metal sheath, metal enclosure or fine mesh metallic grid should be connected to the protective conductor of the supply circuit.
Maximum Zs values
•There are new values based upon a nominal voltage of 230v and not 240v hence the values have been slightly reduced (i.e. 32A Type B - MCB was 1.50 now 1.44).
A new table has been provided giving the maximum values of earth fault loop impedance for RCDs.
Voltage Drop

•The new regulations now provide different voltage drop values for installation supplied from a public supply and private supply (i.e. Own generation). For a public supply the maximum values are 3% for lighting and 5% for other uses, for a private supply the maximum values are 6% for lighting & 8% for other uses.
Disconnection Times
•Final circuits not exceeding 32A shall have a maximum disconnection of 0.4 seconds for a TN-S or TN-C-S (PME) earthing arrangements.
•For TT systems the maximum disconnection time is 0.2 seconds, however a statement is included in the table (41.1) which states "Where disconnection is achieved by an overcurrent protective device, and the protective equipotential bonding, or main equipotential bonding, is correctly installed, the maximum disconnection times applicable to a TN system may be used."
New Sections on:

• 559 - Luminaries and Lighting
• 709 - Marinas and similar locations
• 711 - Exhibitions, Shows and Stands
• 712 - Solar Photovoltaic (PV) Power Supply Systems
• 717 - Mobile or Transportable Units
• 721 - Caravans and Motor Caravans
• 740 - Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses

 

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17th Edition – ( this will help you with your 17th Chaps ,

Part 1: Scope, Object & Fundamental Principles ,

* (134.2.2 ) Designer of Installation responsible for specifying the interval to the first Periodic Inspection ,
* ( 135.1 ) Now makes a Positive Recommendation that every electrical Installation is subject to Periodic and Testing , in Accordance with Chapter 62 : p-162

Part 2 : Definitions ,
“ Competent Person “ ↔ p-22

Part 2 : Definitions , ↔ p-24
* Exposed Conductive part , A Conductive part of Equipment which can be touched and which is not live but which can
Become live when basic insulation fails , Example ( Metal Switch Plate , )
Part 2 : Definitions , ↔ p-24
• Extraneous-conductive parts , and its associated definition , remain unchanged :

************
* Line Conductor ( Replaces Phase Conductor Line is the Internationally used tem ) Do Not Confuse Line Conductor which can be a Neutral Conductor :

Chapter 41 : RCDs ,

* RCDs are now recognised as giving additional protection ( this term is now used instead of Supplementary Protection ) ←←←
* RCD now required for all general use socket-outlets rated up to 20A , allows for 2 Exceptions ←←←
(1) Socket-outlet used under supervision of skilled or instructed persons :
(2) Socket-outlet suitable identified for connection of particular item of equipment :
* To be recognised as giving additional protection The RCD must be rated at 30mA or Less and operate within 40mS
When tested at ( 5 x rated operating current )
Chapter 41 :
Revised Disconnection Times :
* TN-systems – 0.4 seconds ( Final Circuits up to 32Amp : ←←←
* TT-systems – 0.2 seconds ( Final Circuits up to 32Amp - Allows for 0.4s where all Protective bonding in place and
Disconnection is achieved by Overcurrent Device )
* Distribution circuits and circuits not covered by table 41.1 ( TN- = 5 seconds & TT = 1 second ,
* Supplementary bonding can be used were Disconnection Times can Not be Met . ←←←

Chapter 52 :
Selection & Erection of Wiring Systems :

* Chapter 52 now includes reference to Busbar Trunking systems and Powertrack systems :
* Max Value of Voltage Drop in Consumer’s Installations has Changed – Appendix 12 . p-358
Volt drop between origin and load terminals in LV system to be Less than ;
2392-10 ( Public Supply : Lighting 3% …….. Other Uses 5% ,
Private Supply : Lighting 6% …….. Other Uses 8% ,
( These Replace the Current 4% Requirement ) ←←←←←←←←

Chapter 55 :
Luminaires & Lighting ( 559 ) Regs
* Maximum circuit rating 16A for B15 , B22 , E14 , or E40 Lamp Holders ,
* Through wiring only permitted where light is designed for this ,
Chapter 55 :
Luminaires & Lighting ( 559 ) Regs
* 559 applies to selection & erection of luminaires & lighting installations fixed Installations and highway power supplies & street furniture ,
* Outdoor lighting includes : - Roads , Parks , Car-Parks , Gardens , Sporting Areas , Monuments , Floodlighting , Telephone Kiosks ,
Bus Shelters , Advertising Panels , Road Signs & Road Traffic Signals ,
• Excludes , Distributors Equipment & Temporary Festoon lighting ,

Part 6 :
* New part 6 Inspection & Testing Table 71A ↔ Now known as ( Table 61 p-158 )
-&- will ask you this one , ( 0.5MΩ SELV or PELV at 250 volts ) ←←←←

Chapter 62 :
Periodic Inspection & Testing
621.5 : Periodic Inspection & Testing shall be undertaken by a Skilled Person , Competent in such work ,
* Proof of Competence may be required ,

Section 701 : Bathrooms ,
* Section 7 Special Installations or Locations :
* Section 701 Locations, containing a bath or shower ,
* Zone ( 3 ) has been Removed : ←←←←←
* Suitable Equipment can be within 600mm of a bath ,
* Excluding 13amp Sockets to BS-1363 ( p-229 ) which must be 3 Meters from edge of bath or shower , -&- ,
* All circuits to be RCD Protected ,
* Supplementary bonding is NOT required – Provided any Required Protective Equipotential bonding has been installed ,

Part 7 :
Regulation ( 415.2 ) Supplementary Equipotential bonding : in relation to Section 701 , i.e. Locations Containing bath or Shower ←←:

Section 704 : Construction & Demolition Sites :
Section 705 : Agriculture & Horticulture :
• in both sections the reduced disconnection times of ↔ ( 0.2s ) ↔ and ↔ ( 25v ) ↔ Equation have been Removed : ←←←←

Section 708 : Caravan & Camping Parks :
* Sockets-Outlets must be provided individually with overcurrent and RCD protection for each pitch outlet : -&-
( Previously 1 RCD was allowed to protect not more than 3 pitch outlets ,

Tables 41.2, 41.3, 41.4

* If the measured Zs value exceeds 80% of the given values, a more precise measurement may have to be made to satisfy the requirements of BS-7671 . p361 :
* BS-7671 does not give maximum Zs values for BS 3871 mcb's. :
* If the maximum Zs value for a circuit in a TN- system cannot be met, the circuit may be protected by a 30ma RCD . 531.3.1
* If the maximum Ze value for a TN- system cannot be met, the installation may be protected by a 100ma RCD and treated as a TT- system. 531.3.1, 411.5.1, 411.5.2, 411.5.3 :

RCD :
the maximum disconnection time allowed for a RCD protected socket for a caravan/tent pitch :
Please refer to BS 7671:2008 Reg 708.553.1.13, this refers to Reg: 415.1.1, ( 30mA RCD 40mS at 5 x 30mA. )

17th Edition requirements for the testing of RCDs :

The 17th Edition of the Wiring Regulations (BS 7671: 2008) will introduce a number of new requirements for the installation of RCDs, therefore it is timely to look at the requirements within the 17th Edition for verification of RCDs.
The continuing effectiveness of these RCDs needs to be confirmed periodically. This article discusses the verification required where RCDs are used to provide automatic disconnection of supply in the event of a fault and additional protection. It should be stated at this point that the 17th Edition does not introduce any significant changes in the requirements for the testing of RCDs even where they are installed to provide automatic disconnection in the event of a fault.
Use of RCDs to achieve automatic disconnection in case of a fault 411.3.2.1 requires (in most cases) that a protective device shall interrupt the supply to a line conductor of a circuit or equipment in the event of a fault of negligible impedance between said line conductor and an exposed conductive- part or a protective conductor for the circuit or equipment within the appropriate required disconnection time. A disconnection time of 5 seconds for distribution equipment and final circuits of rating exceeding 32A is permitted by 411.3.2.3. Similarly, a disconnection time of 1 second for distribution equipment and final circuits of rating exceeding 32 A is permitted by 411.3.2.4.

Does the 17th Edition require a new test for RCDs ?

The rumour seems to have originated from Note 2 of Table 41.1 of the 17th Edition, with gives maximum permitted disconnection times for final circuits rated at up to 32A. The note states that: ‘Where compliance with this regulation is provided by an RCD, the disconnection times in accordance with Table 41.1 relate to prospective residual fault currents significantly higher than the rated residual operating current of the RCD.
BS 7671: 2008 (IEE Wiring Regulations 17th Edition) was published in January and comes into effect on 1st July. A rumour has been circulating amongst electrical contractors that the 17th Edition requires RCDs to be subjected to a test at twice their rated residual operating current (2 x I∆n ). Is this the case ?


As explained in this article, the familiar currents of 0.5 x I∆n , 1 x I∆n, and 5 x I∆n, (as applicable) should be all that are needed when testing RCDs in the vast majority of installations, as is the case under the 16th Edition.

A 2 x I∆n, test would be needed only in exceptional circumstances. But, even where this is the case, it does not necessarily mean that an RCD test instrument having a 2 x I∆n, test setting is required.

The rumour seems to have originated from Note 2 of Table 41.1 of the 17th Edition, with gives maximum permitted disconnection times for final circuits rated at up to 32 A. The note states that: ‘Where compliance with this regulation is provided by an RCD, the disconnection times in accordance with Table 41.1 relate to prospective residual fault currents significantly higher than the rated residual operating current of the RCD (typically 2 x I∆n ).’ However, Note 2 does NOT mean that a 2 x I∆n test is required.

 

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-&- ( 2391-301 Inspection, Testing and Certification of Electrical : Installations report – ( -&- March 2009 :

It would appear that candidates are still unaware that a working knowledge of Guidance Note 3 and BS 7671:2008 is required to achieve success in this qualification. Many candidates demonstrated significant gaps in both technical and underpinning knowledge of the subject matter. In particular the interpretation of information and test results and the validation process for test results are areas of concern.

From the information given by candidates it is apparent that they may be aware of the need for inspection and testing, but have little understanding of the reasons why it is done or the interpretation of the results obtained.
Many candidates did not display the required knowledge when answering the questions and this would suggest they do not have the necessary knowledge, understanding and experience when entering this qualification.

Use of correct terminology :
Correct terminology must be used when answering questions. Candidates continue to use incorrect terminology. This does indicate that candidates are not aware of the underlying requirements and processes. Typically candidates still referred to a periodic inspection and testing report as the type of inspection and the Electricity at Work Regulations is still incorrectly referred to as the Electricity at Work Act. Candidates also continue to use incorrect titles for documents and publications and to use inappropriate titles for the forms of certification
Documentation :
Some candidates were unable to identify the correct title of documents for certification, and many still refer to a Periodic Inspection Certificate. Candidates were unable to correctly identify the
Schedules by title with a Schedule of Items Inspected and a Schedule of Tests being common incorrect alternatives.
Questions which required candidates to identify where information is to be recorded on the forms of certification produced results which appear to indicate the candidates are not familiar with both the compilation and the content of these forms.
Many candidates did not consult with the third party (licensing authority) when determining the extent and limitations.
Inspection :
Question 22 asked candidates to identify three particular areas for investigation during inspection due to the nature of the location in the kitchen, laundry and residents rooms. The responses to this question were exceptionally poor with many candidates simply listing items such as sockets and switches for all locations giving no indication of the particular areas of investigation. Others included tests and many demonstrated a lack of understanding of the requirements for the locations. Many believed that some type of non-specific bonding was required.
Considering the information provided in the scenario there were very few candidates who identified inspection related to corrosion, appropriate IP ratings damage and the like. In the residents rooms many candidates considered the equipment being PAT tested etc as appropriate items for their inspection.
The response to this question generally indicated a lack of understanding of the inspection process and the information provided in GN3 related to the inspection of installations.
Question 4 required candidates to identify reasons why a survey would be required before a periodic inspection could be undertaken. Very few candidates were able to identify the relation to information not being available. Most identified events that could give rise to a periodic inspection being required.
Testing :
The common misunderstandings identified above show that ring final circuit testing is still a problem for many candidates. There is also some confusion as to the required tests fro particular circuits with many quoting the standard list, and the range of values expected for the tests undertaken. The test process and the expected results are fundamental to the requirements of those undertaking inspection and testing and for the candidates to complete the practical assessment.
Calculations :
Many candidates had problems with calculations related to the inspection and testing process. Cumulative insulation resistance values, determining values for stage 2 and stage 3 of the ring final circuit continuity test from given information caused some difficulty. These calculations are typical of the type of evaluations which may be required during the verification of test results. As these are fundamental to the activities of initial verification and periodic reporting such calculations should be within the abilities of the candidates. It would appear that a number of candidates do not understand the effects of resistances in series and parallel.

Describing test procedures :
When describing how to carry out a test, candidates were often confused as to what was required, unable to describe a logical approach and rarely used large clear diagrams to assist with their description. 2391-
Drawings and labels :
Question 25 required candidates to provide a fully labelled diagram of the earth fault loop path for a radial circuit. The scenario identified the system as TN-S. Whilst some candidates used the incorrect system there was a general lack of clear drawing and labelling.

Section A :

In Section A there were many fundamental errors identified in candidate responses. Typically many candidates

• identified a shock risk when testing main protective bonding conductors and not the tripping hazard. If the procedure is correct (isolation of the installation) there is no shock risk.

• could not correctly identify the reason for carrying out a continuity of ring final circuit test.

• could not identify special locations which were classified in zones; this including listing locations such as caravan sites and construction sites.

• were unaware of the IP requirement for Basic Protection with most examples related to ingress of liquids.

• were unable to determine the recorded RA value from given data, many adding the three values in parallel.

• did not know why R1 + R2 cannot be determined using Zs – Ze. Despite this information being given in Question 16 of Section A, many then went on in Section B to determine R1 + R2 using this incorrect method.

• were unable to identify the connection points for the instrument leads when measuring Ze when using a three lead test instrument.
• could not determine the maximum Zs for a 300 mA RCD to meet the requirements of BS 7671
• could not correctly determine the maximum permitted voltage drop for given circuits. Many used 16th edition values and/or determined voltage at equipment terminals.

Section B :
In Section B there were some areas where candidates were unable to demonstrate their understanding of the subject.

Many candidates were unable to

• identify operational aspects which would affect the inspection and testing activity with many simply identifying locations which were given in the scenario without identifying the aspect.

• identify the correct test sequence and relate instruments and ranges for the tests. For a radial final circuit the candidates included main protective bonding conductors, ring final circuit continuity and polarity with an approved voltage indicator in the dead tests, and PFC and RC in the live tests.

• describe the ring final circuit continuity test with may carrying out Stage 2 & 3 linking one pair (L1 & N2) and testing across the other pair for each test. Some included this as an extra stage wasting time and effort. A number were unable to determine the expected values.
• determine the calculated values of R1 and R2 correctly with a surprising number incorrectly using Zs – Ze despite the information in Part A that this method could not be used. Most candidates failed to appreciate that two of the circuits were ring final circuits and therefore failed to divide their result by 4.

Exam technique – time management :
Time management for candidates is important to ensure they have an opportunity to achieve the best possible result. Considering the number of marks available for each question and using this determine the extent and depth of the answer required would be useful. 2391-
As a guide, candidates should spend approximately one minute on an answer for each possible mark to be awarded. A question worth three marks for example should take approximately three minutes to complete. However many questions in Section A will take considerably less than this.

Exam technique – read the question
Careful reading of the question is important. Many answers did not include the information requested and candidates often provided answers which did not correspond to the question posed.
Candidates often did not answer the questions in both Sections A and B of the paper in relation to the given information and this often resulted in the loss of marks. Candidates must read the information given in the question. 2391-

 

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C&G 2382. 17th Edition ( BS7671:2008 ) Examination :

1. The Regulations (BS7671:2008) do NOT apply to
a. Residential Premises
b. Industrial Premises
c. Lightning Protection
d. Street Furniture
2. The Regulations do apply to
a. Offshore Installations
b. Mines & Quarries
c. Lift Installations
d. Low Voltage Generators
3. Which of the Following documents are deemed Non- Statutory
a. BS7671:2008
b. EAWR 1989
c. HASAW 1974
d. ESQCR 2002
4. Parts 3 – 7 of BS7671:2008 are explained in rudimentary terms within
a. Chapter 13
b. Chapter 12
c. Part 3
d. Appendix 5
5. Basic protection is defined as
a. Protection against shock under fault conditions
b. Protection against shock under fault free conditions
c. Protection against contact with live parts under fault free conditions
d. Protection against faults under sound electrical conditions
6. Equipment in which protection against electric shock does not rely on basic
insulation only is described as
a. Double Insulated Equipment
b. Class I Equipment
c. Class II Equipment
d. Class III Equipment
The7. The Earthing System illustrated in Figure 1 below would be identified as a
a. TN-S
b. TT
c. TN-C-S
d. IT
8. A Voltage of 250Volts AC (rms) would be defined as
a. Band I
b. Extra Low Voltage
c. High Voltage
d. Low Voltage
9. In determining Maximum Demand, ‘Diversity’ may be applies, which is
a. Taking the sum of all the protective devices from any CCU
b. Taking into account that not all loads will be switched on at the same time
c. Taking into account that all loads doubtless will be engaged at the same time
d. Ensuring that an economical and reliable design preference is utilised.
10. Every Installation is divided into circuits in order to
a. Ensue simplicity of isolation
b. Comply with European Standards
c. Avoid hazards and prevent inconvenience in the event of a fault
d. Allow individual energising of circuits which are not isolated
11. A building made entirely out of wood would be categorised for External Influences as
a. CA2
b. CA1
c. CB3
d. CB4
12. The Maximum Disconnection time for an a.c. TN circuit rated at 230V is
a. 0.04 seconds
b. 0.1 seconds
c. 0.4 seconds
d. 0.2 seconds
13. The Maximum Zs for a BSEN60898 Type C circuit breaker rated at 16Amps with
a 0.4second disconnection time is
a. 2.87Ω
b. 1.44Ω
c. 0.72Ω
d. 1.15Ω

14. For a TT System the Maximum earth fault loop impedance for a 100mA
BSEN61008-1 RCD in a 230Volt circuit is
a. 500Ω
b. 460Ω
c. 167Ω
d. 100Ω
15. Where, on electrical equipment, must the symbol in figure 2 be present
Figure 2
a. Where basic and supplementary earthing is present on an appliance
b. Where supplementary earth-bonding to an appliance is not present
c. Where electrical equipment has basic insulation only
d. Where Class I equipment is served from a sub-main CCU
16. Where Basic Protection is employed in the form of a barrier or enclosure, any
horizontal top surface must meet a protection level of at least
a. IPDXX
b. IP2X
c. IPXX3
d. IP4X
17. Except if made from adequate material, a luminaire rated at 200Watts should be
located away from combustible material by
a. 0.3m
b. 0.5m
c. 0.8m
d. 1.0m
18. To avoid burning, a non-metallic part intended to be touched but not hand held
cannot exceed
a. 80°C
b. 85°C
c. 90°C
d. 95°C
19. In relation to Voltage Disturbances, the resistance of the earthing arrangement
at the Transformer is referred to, within the area of symbols, as
a. RA
b. RB
c. RD
d. RE
20. Every core of a cable shall be identifiable at its terminations and preferably
throughout its length by
a. colour code only
b. letter code only
c. number code only
d. one or more of the above
21. An appropriate colour for a PEN conductor should be:
a. blue through its length with green markings at the terminations
b. green & yellow through its length with blue markings at the terminals
c. green & yellow through its length with brown markings at its terminals.
d. Green through its length with yellow markings at the terminals
22. A permanent label with the words ‘Safety Electrical Connection – Do Not
Remove’, complies with:
a. BS728
b. BS1363
c. BS951
d. BS423
23. A cable buried underground but not in conduit or ducting for mechanical
protection must incorporate
a. An earthed armour or metal sheath or both
b. A surface covering of 50mm thickness paving stones
c. A clear surface warning notice informing of its location
d. A PVC outer sheath
24. The de-rating factor for a cable surrounded by 50mm of thermal insulation is
a. 0.88
b. 0.78
c. 0.63
d. 0.51
25. In an L.V installation supplied directly from a public L.V distribution system the
maximum volt drop on a lighting circuit between the origin and any load point
should be no greater than
a. 6% Uo
b. 5% Uo
c. 4% Uo
d. 3% Uo

26. Every electrical inspection shall be accessible for inspection, testing and
maintenance purposes except for which of the following
a. A connection made in a junction box beneath floorboards
b. A connection made within a motor control unit
c. A connection designed to withstand fault current
d. A compound filled or encapsulated joint
27. The rated RCD operating current of such a device installed as a protection
against risk of fire in a TT system shall have a value of
a. 30mA
b. 100mA
c. 300mA
d. 500mA
28. The maximum prospective short circuit or earth fault current in a circuit should
not exceed
a. The operating current of circuit switching devices
b. The rated breaking capacity of any associated protective device
c. The design current of the circuit
d. The rated operating current of any RCD in circuit
29. Which of the following switching devices may be satisfactorily utilised for the
purposes of isolation?
a. BSEN60669-2-4
b. BSEN60669-2-3
c. BSEN60669-2-1
d. BSEN60669-1
30. When using bare conductors in extra low voltage lighting installations supplied
from a safety isolating transformer the minimum permissible cross sectional
area of conductors must be
a. 1.5mm2
b. 2.5mm2
c. 4mm2
d. 6mm2
31. Suspension devices for ELV luminaries must in any case be capable of
supporting at least
a. 5 Kg
b. 7.5 Kg
c. 10 Kg
d. 20 Kg
32. An automatic electrical safety service supply classed as medium break must, in
the event of losing the main supply, instate the safety service supply in a time
period of
a. between 0.15 & 0.5 seconds
b. between 0.5 & 5 seconds
c. between 5 & 15 seconds
d. greater than 15 seconds
33. The minimum value of Insulation Resistance for a 230Volt system must be
a. >0.25 MΩ
b. >0.5 MΩ
c. >1.0 MΩ
d. >2.0 MΩ
34. Correct Polarity must ensure that every ES lamp-holder have their outer or
screwed contacts connected to the neutral conductor, except for
a. E14 & E27 Lampholders
b. E14 & BSEN60895 Lampholders
c. E27 & BSEN61009 Lampholders
d. E11 & E24 Lampholders
35. To comply with PART 6 of BS7671, Periodic Inspection & Testing shall be
specifically undertaken by
a. A formally qualified Test Engineer
b. A person deemed as the ‘Duty Holder’ of the company carrying out the work
c. A expressly skilled person
d. A competent person
36. Zone 2 of a bathroom is restricted to the highest water outlet or the horizontal
plane lying above finished floor level by
a. 3.00m
b. 2.50m
c. 2.25m
d. 2.00m

37. In Zone 3 of a Sauna equipment must be able to withstand a minimum
temperature of
a. 100°C
b. 120°C
c. 125°C
d. 170°C
38. In marinas, equipment installed above a jetty or wharf, which is likely to
encounter water jets, shall be selected to comply with external influence levels
of
a. (AD4): IPX4
b. (AD5): IPX5
c. (AD6): IPX6
d. (AE6): IPX5
39. For a BS88-2.2 Fuse rated at 25A to obtain a 0.4sec disconnection time, it would
require a minimum prospective fault current of
a. 160A
b. 130A
c. 100A
d. 85A
40. A 30Amp Semi Enclosed BS3036 Fuse receiving a prospective fault current of
130A would disconnect in
a. 5.0sec
b. 1.0sec
c. 0.4sec
d. 0.2sec

Answers:
1. C Part 1 -110.2 Page 13
2. D Part 1 -110.1 Page 12
3. A Part 1 -114.1 Page 13
4. A Part 1 -120.3 Page 14
5. B Part 2 - DEFENITIONS
6. B Part 2 - DEFENITIONS
7. C Part 2 - DEFENITIONS
8. D Part 2 - DEFENITIONS
9. B Part 3 - 311.1 Page 38
10. C Part 3 - 314.1 Page 39
11. A Appendix 5 Page 319
12. C Part 4 - Table 41.1 Page 46
13. B Part 4 - Max Zs Tables - Part 4
14. B Part 4 - Table 41.5 Page 50
15. C Part 4 - 412.2.1 Page 55
16. D Part 4 - 416.2.2 Page 60
17. C Part 4 - 422.3.1 Page 67
18. A Part 4 - Table 42.1 Page 69
19. D Part 4 - 442.1.2 Page 80
20. D Part 5
21. B Part 5
22. C Part 5
23. A Part 5
24. A Part 5 – Table 52.2 Page 104
25. D Part 5
26. D Part 5
27. C Part 5
28. B Part 5
29. A Part 5
30. C Part 5
31. A Part 5
32. C Part 5
33. C Part 6 - Table 61 Page 158
34. A Part 6 - 612.6 Page 159
35. D Part 6 - 621.5 Page 162
36. C Part 6 - Page 169
37. C Part 7 - 703.512.2. Page 180
38. B Part 7 - 709.512.2.1.1 Page 193
39. A Appendix - Time/Current Graph - Page 248
40. C Appendix - Time/Current Graph -Page 245

Symbols :
In Rated current of the contacts - Expressed in amperes e.g. 100A.
I?n Sensitivity or residual operating current - Usually expressed in amperes e.g. 0.03A for 30mA

 

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Regulation 411.5.3 requires that for TT systems the
formula in 411.5.3 (ii) RA I∆n & 50 V.

RCD maximum Zs or RA values
……… maximum touch voltage
I∆n (A)………. 50V
0.01 …………. 5000Ω
0.03 …………. 1666Ω
0.1 ……………. 500Ω
0.3 ……………. 166.6Ω
1 ………………. 50Ω
3 ………………. 16.66Ω

Earth electrode resistances over 200Ω are likely to be unstable
( Measured Résistance should not exceed 100Ω ,

( RA I∆n ≤ 50 V : R ≤ 50v / 30mA , ( 50 ÷ 30 = 1667Ω
R ≤ 50v ÷ 160 = 0.31Ω ( 30mA RCD protects a.c Circuit rated residual current 30mA ,

411.5.4 : ( Zs x Ia ≤ Uo ) 32A = ÷ 230 = 0.13Ω
TT , 50v ÷ .3mA = 166.7 Ω , ( 30mA )
100mA = ) 50v ÷ 0.1mA = max Zs off 500Ω

612.9 : Earth fault loop impedance, Zs

This may be determined either by Direct Measurement at the further point of a live circuit OR by adding (R1 + R2) Ze

i.e. Zs = Ze + ( R1 + R2 ). In general, the Earth Fault Loop Impedance shall Not Exceed 100 Ω.

17th Edition Forms : 2392-10

1 Initial inspection and testing 2392-10

Forms 1 to 4 are designed for use when inspecting and testing a new installation, or an alteration or addition to an existing installation. The forms comprise the following:
1 Short form of Electrical Installation Certificate (To be used when one person is responsible for the design, construction, inspection and testing of an installation.)
2 Electrical Installation Certificate (Standard form from Appendix 6 of BS 7671)
3 Schedule of Inspections
4 Schedule of Test Results.
Notes on completion and guidance for recipients are provided with the form.

2 Minor works 2392-10
The complete set of forms for initial inspection and testing may not be appropriate for minor works. When an addition to an electrical installation does not extend to the installation of a new circuit, the minor works form may be used. This form is intended for such work as the addition of a socket-outlet or lighting point to an existing circuit, or for repair or modification.
Form 5 is the Minor Electrical Installation Works Certificate from Appendix 6 of BS 7671.
Notes on completion and guidance for recipients are provided with the form.

3 Periodic inspection 2391-10
Form 6, the Periodic Inspection Report from Appendix 6 of BS 7671, is for use when carrying out routine periodic inspection and testing of an existing installation. It is not for use when alterations or additions are made. A Schedule of Inspections (3) and Schedule of Test Results (4) should accompany the Periodic Inspection Report (6).
Notes on completion and guidance for recipients are provided with the form.

2392-10

Prospective short circuit current is the greater of the short-circuit current and earth fault current -&- :
Ze, the external impedance measured at the origin of the installation with the main bonding disconnected. -&- :

Continuity of protective conductors - Every protective conductor including bonding conductors shall be tested to verify it is sound and correctly connected :

Continuity of final circuit conductors - The sum of the resistance of the of the phase conductor (R1) and the protective conductor (R2 ) i.e. R1 + R2 , is to be inserted : This may be use, after temperature correction, by adding to Ze , to determine Zs.

Insulation resistance :

Equipment such as electronic devices shall, where necessary, be disconnected from the installation to avoid damage during testing. Where required, such equipment shall be tested separately.

17th Edition wiring regulations, explains : 2392-10

There is also a specific requirement for appropriate documentation for all installations.
Of particular interest to the health and safety manager, Regulation 134.2.1 requires that inspection and testing must be carried out by a 'competent person' to verify that standards have been met.
Importantly, a 'competent person' is defined as someone 'who possesses sufficient technical knowledge and experience for the nature of the electrical work undertaken and is able at all times to prevent danger, and where appropriate, injury to themselves and others'.
In practice, this means that inspection and testing should only be taken by experienced engineers that are qualified to the City and Guilds 2392 - 10 course 'Fundamental Testing, Inspection and Initial Verification'.
This course is now recognized as the qualification for competent persons carrying out initial inspection and testing of electrical installations.
For periodic inspection and testing, competent persons should successfully complete the C&G 2392 - 20 'Inspection, Testing and Certification of Electrical Installations' course in addition to the 2392 - 10 course.
Once the initial verification of the installation has been completed, which includes both inspection and testing, the regulations call for the issuing of an Electrical Installation Certificate, together with a schedule of test results and a schedule of inspections.
The certificate includes space for three signatures - the person responsible for the design, the person responsible for the construction and the person carrying out the inspection and test of the installation.
It should be emphasized that the signature for the inspection and test section is the person who actually carries out the inspection and test and not someone else who may be in authority.
In some cases, all three sections may require signature by the same person and this is perfectly acceptable.
However, the Electrical Installation Certificate should not be signed until any defects identified by the person responsible for inspection and test have been corrected.
An Electrical Installation Certificate (or a Minor Electrical Installation Works Certificate), stating the extent of the works covered, shall be issued once the inspector is satisfied that the works comply with the regulations.
Any defects found in related parts of the installation, not affecting the safety of the alteration or addition should be reported in writing to the person ordering the work.
If existing defects affect the new work then these defects need to be corrected before an Electrical Installation Certificate can be issued and before the new work can be put into service.
An example of this is where bonding or equipotential bonding is inadequate or omitted, as this would seriously affect the safety of the whole installation, including the new work.
The Electrical Installation Certificate should not be used for periodic inspections.
The 17th Edition regulations stipulate that the designer of the installation is responsible for specifying the interval to the first periodic inspection and test.
There is also the positive recommendation (Regulation 135.1) that every electrical installation is subject to periodic inspection and testing by a competent person (in accordance with Chapter 62).
For example, the IEE Guidance Note for periodic fixed installation test frequencies advise a maximum period of five years between inspections and testing for commercial offices, shops and hospitals - reducing to three years for industrial facilities, leisure complexes and theatres.
For some special installations, such as swimming pools, petrol stations and caravan parks, the maximum period between inspections and testing is one year.
This represents a substantial difference from the previous edition, which presumed that a programme of risk assessments, records and preventative maintenance could be adopted in place of periodic testing.
The Periodic Inspection Report form is only to be used for the inspection of an existing installation and should include both inspection and test results.
Again the extent and limitations of the report needs to be stated and recommendations of defects and their remedies should be made.
The report includes a numbering system for this purpose, as follows: 1 - Requires Urgent Attention; 2 - Requires Improvements; 3 - Requires Further Investigation; and 4 - Does Not Comply With BS 7671:2008 (although this does not necessarily imply that the electrical installation is unsafe).
A minor works is defined as 'work which does not include the provision of a new circuit'.
Testing is still essential and a number of tests are specifically identified as essential to confirm safety.
Also included on the form is space to allow the inspector to comment on the existing installation.

.

 

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17th Edition wiring regulations, explains :
“Earthing Arrangements “
1. Earthing Arrangements
2. In this section we are going to look at : -
The basics of shock .
Shock protection .
Class 1 & Class 2 equipment .
The three common earthing arrangements .
3. Earthing arrangements -
4. Definitions from Part 2 BS 7671
5. Bonding conductor A protective conductor providing equipotential bonding
6. Where protection against electric shock does not rely solely on basic insulation alone. Exposed-conductive parts being connected to a protective conductor within the fixed wiring of the installation. Class I equipment Class I insulation Single-layer insulation Live part Exposed conductive part
7. Class II equipment Where protection against electric shock relies on the application of additional or supplementary insulation. There is no provision for the connection of a protective conductor to exposed metalwork. Class II insulation Live part Two layers of insulation Exposed metalwork
8. Double insulation Double insulation (Class II) - Insulation comprising both basic insulation and supplementary insulation Symbol found on equipment
9. Earth The conductive mass of Earth, whose electric potential at any point is conventionally taken as zero
10. Earth Electrode A conductor or group of conductors in intimate contact with, and providing an electrical connection to earth
11. Earth electrode resistance The resistance of an earth electrode to earth
12. Earth fault current A fault current which flows to earth
13. Earth fault loop impedance The impedance of the earth fault current loop  starting and ending at the point of earth fault. Symbol Z Unit
14. The earth fault loop The earth fault loop starting at the point of fault consists of:
o The circuit protective conductor (c.p.c.)
o Consumers earthing terminal and earthing conductor
o For TN systems, the metallic return path
o For TT and IT systems the earth return path
o The path through the earthed neutral point of the
o transformer
o The transformer winding and phase conductor to point
o of fault
15. Earth leakage current A current which flows to earth, or to extraneous conductive parts, in a circuit which is electrically sound. This current may have a capacitive quality including that from the deliberate use of capacitors for noise filtration.
16. Earthed equipotential zone A zone within which exposed conductive parts and extraneous conductive parts are maintained at substantially the same potential by bonding, such that under fault conditions, the differences in potential simultaneously accessible exposed and extraneous- conductive parts will not cause electric shock.
17. Earthing Connection of the exposed conductive parts of an installation to the main earthing terminal of that installation
18. Basic contact (shock) Results from Making contact with parts of a circuit or system which are live under normal conditions
19. Earthing Connection of the exposed conductive parts of an installation to the main earthing terminal of that installation
20. Extraneous conductive part A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.
21. Fault A circuit condition in which current flows through an abnormal or unintended path. This may result from an insulation failure or a bridging of insulation. Conventionally the impedance between live conductors or between live conductors and exposed or extraneous conductive parts at the fault position is considered negligible.
22. Functional earthing Connection to Earth necessary for proper functioning of electrical equipment Table 51A Functional earthing conductors to be coloured cream
23. Contact of persons or livestock with exposed-conductive parts which have become live under fault conditions. Fault contact
24. Protective conductors A conductor used for some measure of protection against electric shock and intended for connecting together any of the following parts
o Exposed conductive parts
o Extraneous-conductive parts

17th Edition : Earthing & Equipotential Bonding :

Earthing ,

Earthing ensures that in the event of a fault, adequate fault current will flow causing rapid operation of a Circuit Protective Device (fuse, circuit breaker, or RCD) promptly disconnecting the supply. This limits the duration of any shock that one might receive, dramatically reducing the risk of serious injury or death :

For example, suppose a poorly positioned live wire in a washing machine becomes abraded by a sharp metal edge when the machine is running and this has the effect of making the casework of the machine "live". Since the case is connected (via its 13A plug) to mains earth, a high current will flow which will either blow the fuse in the plug and/or trip the RCD protecting the circuit :

During fault conditions, earthing may also reduce the voltage rise of anything earthed, which in addition to the limiting of the shock duration described above can also reduce the shock risk :

On general purpose socket circuits, the size of earthing conductors, and the circuit protective devices used are chosen to ensure that a fault is cleared within 0.4 seconds (or 0.2 seconds if the installation uses TT Earthing). For submains or higher power circuits feeding fixed equipment the time limit is 5 seconds (or 1 with TT) :

Main Equipotential Bonding ( 17th Edition , Main Protective Bonding Conductor )

Main bonding is the electrical interconnection of incoming (metallic) services (e.g. water, gas, and oil pipes) plus any extraneous conductive parts of a building (like the metal framework used in some buildings, or the central heating pipework), to the main electrical earth. This ensures that under fault conditions extraneous conductive parts, such as pipework, are not able to take on a dramatically different electrical potential to that of the installation's earth connection :

Supplementary bonding ( 17th Edition , Supplementary Protective bonding conductors’ / where required ,

Supplementary, or cross bonding is usually found in special locations containing a bath or shower. Unlike earthing it is not designed to clear a fault. What it does is electrically tie together all accessible conductive parts (pipes, taps, electrical appliances etc) that could under fault conditions introduce a dangerous potential (voltage) into the room :

For example suppose an electrically heated towel rail develops a fault which makes it electrically live. (Of course this also supposes that it is not earthed properly: which should never happen but the regulations adopt a belt and braces approach). Without bonding, such a fault would result in the towel rail being at mains voltage, while adjacent basin taps might offer a path to earth via the water pipework. This would be a very dangerous situation since touching both towel rail and a tap would expose one to a 230V potential difference across the arms and chest (including heart) probably causing severe injury or death :

However if the pipework feeding both hot and cold taps is bonded together with that of the earth of any electrical circuits supplying the room, then the towel rail fault will try to bring both taps up to mains voltage (230V). However touching both rail and tap at the same time exposes one to a potential difference of zero volts :

(Actually the bonding may fail to tie all elements together at exactly the same potential, but it is designed to limit any potential difference to 50V or less) :

The 17th Edition and Earthing & Equipotential Bonding

* Before an addition or alteration can be made to an existing installation it must be ascertained that the earthing and bonding arrangements comply with the current version of BS7671 and any existing equipment including the incoming supply is adequate for the proposed addition or alteration. 131.8
* Every installation must be provided with a main earthing terminal. 542.4.1
* The main earthing terminal, all bonding conductor connections and connections to an earth electrode must be permanently labelled 'Safety Electrical Connection - Do Not Remove'. 514.13.1
* Every joint and connection must be accessible. 543.3.3, 526.3
* All circuits must have a cpc that is terminated at each wiring point and at each accessory. 411.3.1.1

 

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* Rigid metal conduit and the metal sheath or armour of a cable can be used as a protective conductor. 543.2.2, 543.2.5
* Where rigid metal conduit or the metal sheath or armour of a cable is used as a protective conductor, a separate protective conductor must connect the earthing terminal of any accessories to the appropriate metal backbox. 543.2.7, 543.7.2.1

* All joints in metal conduit must be continuous. 543.3.6
* The cpc of flat cables must be sleeved when the cable sheath has been removed. 543.3.2
* Protective conductors must be identified by the colours green & yellow. 514.4.2 The single colour green is not permitted. 514.4.5
* In most domestic installations switches are not to be used with a protective conductor. 543.3.4
* All exposed-conductive-parts of a TN installation must be connected to the main earthing terminal. 411.4.2
* All extraneous conductive parts in an installation must be connected to the main earthing terminal by main protective bonding conductors. This applies to the metallic sheath of a telecommunication cable where permission from the owner of the cable must be obtained. 411.3.1.2
Main Earthing Conductor :
* The minimum csa of the main earthing conductor must be determined by the adibiatic equation or selected from Table 54.7 543.1.1. If the adibiatic equation is used, the minimum csa of the main earthing conductor must be 6mm 544.1.1. Table 54.7 suggests a 16mm main earthing conductor for phase conductors with a csa of up to 35mm.
* The csa of the main earthing conductor where PME conditions apply should be not less than that for a main protective bonding conductor (10mm) for the same installation 544.1.1. Invariably the electricity supplier will provide a 16mm main earthing conductor for a PME supply in a domestic property.
Main Protective Bonding Conductors :
* All extraneous conductive parts in an installation must be connected to the main earthing terminal by main protective bonding conductors. This applies to the metallic sheath of a telecommunications cable where permission from the owner of the cable must be obtained. 411.3.1.2
* For TN-S or TT systems the csa of main protective bonding conductors must be a minimum of 6mm and not be less than half the csa of the main earthing conductor. 544.1.1
* For a PME system the csa of the main bonding conductors must not be less than that given in Table 54.8 i.e. a 10mm protective bonding conductor for a neutral conductor of 35mm or less. 544.1.1
* For a service pipe, the main bonding conductor should be connected as near as possible to the point where the service enters the building. The connection must be before any branched pipework and on the consumers side of any meter. If possible the connection should be made within 600mm of the meter outlet. Where the meter is outside, the bonding connection should be made at the point of entry of the service into the building. 544.1.2

* Main bonding conductors should not be supported by the service pipes they are connected to. 543.3.1
* Where a main bonding conductor loops in and out to connect to an extraneous-conductive-part, the conductor should be unbroken at the connection. 528.3.3
* It is not necessary to run a main protective bonding conductor to an incoming service where the incoming service pipe and the consumers pipework are both made of plastic. If the incoming service pipe is made of plastic and the consumers pipework is made of metal it is recommended to main bond any metal pipework. OSG p29
Supplementary Bonding Conductors :
* Supplementary bonding is not required in a bath or shower room if all the extraneous conductive parts of the installation are connected to the main equipotential bonding. p6, 701.415.2
It is not generally required to supplementary bond the following :
* kitchen pipes, sinks, draining boards, metallic kitchen furniture, boiler pipes, metallic parts supplied by plastic pipes or metal pipes to hand basins or wc's ( excluding metal waste pipes in contact with earth ). OSG p31
Earth Electrodes : ( 542.2 – 542.2.1 )
* All of the following can be used as earth electrodes :
* Earth rods or pipes * Earth tapes or wires * Earth plates * Underground structural metalwork embedded in foundations * Welded metal reinforcement of concrete embedded in the Earth (excluding pre stressed concrete) * Lead sheaths & metal cable coverings provided the following conditions are met :
* a - the cable covering must be in effective contact with Earth
* b - the permission of the cable owner must be obtained
* c - the owner of the cable must be able to inform the owner of the installation of any changes to the cable which may affect it suitability as an earth electrode
* metal gas or water pipe must not be used as an earth electrode. 542.2.4

Why is inspection and testing necessary ?

Periodic inspection and testing is necessary because all electrical installations deteriorate due to a number of factors such as damage, wear, tear, corrosion, excessive electrical loading, ageing and environmental influences. Consequently legislation requires that electrical installations are maintained in a safe condition and therefore must be periodically inspected and tested.
Licensing authorities, public bodies, insurance companies, mortgage lenders and others may require periodic inspection and testing of electrical installations.
The law and inspection and testing

17% of all house fires are caused by electrical faults, due to lack of maintenance, poor and / or DIY work.

Existing domestic electrical installations are recommended to be inspected and tested at least once every 10 years or 5 years for rental properties. The purpose of this is to ensure the ongoing safety and efficiency of the installation, and to rectify any faults or degradation identified during the work.

It is also recommended that all in-service equipment is also regularly tested and inspected, labelled and records kept

Many house buyers may require a report regarding the age, condition and suitability of the electrical installation for mortgage and / or insurance purposes. This type of report can also be used as a bargaining point where the installation is found to be substandard.

 

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Introduction to the Changes : Apprentices

BS7671:2008 is the current national standard for all electrical work undertaken in
the United Kingdom. The first edition of BS7671 was published in 1992 and has
so far been amended six times. The 17th Edition is the result of a complete
review of the 16th Edition and aims to standardise the UK standards with the
Harmonised Documents (HD’s) produced by the European Committee for
Electrotechnical Standardisation (CENELEC).
A new informative note in the preface advises that publication of the
2008 edition of BS7671 does not automatically mean that installations complying
with previous editions are unsafe for continued use or need to be upgraded.
Numbering. The Regulation numbers are changed so as to be in line with
International Electrotechnical Commission (IEC) Numbers. This enables users to
readily relate UK regulations with European HDs and IEC regulations.
Fundamental Principles. Requirements are added for protection for persons and
livestock against injury, and property against damage caused by voltage
disturbances and electromagnetic influences.
Protection against electric shock – chapter 41.
• The chapter has been rewritten. Many regulations are worded differently but
the requirements are not significantly changed.
• The terms ‘Direct Contact’ and ‘Indirect Contact’ are no longer used. They are
replaced with Basic Protection and Fault Protection. ‘Basic protection’ is
protection against touching live parts. ‘Fault protection’ is protection against
receiving a shock from conductive parts that have become live due to a
breakdown of insulation or damage to equipment.
• Socket outlets rated not exceeding 20 A and intended for general use by
ordinary persons must be protected with 30 mA RCDs. This means that
general purpose sockets in domestic and similar properties must have
RCD protection.
• External sockets rated not exceeding 32 A must also have 30 mA
RCD protection.
• Maximum permitted earth loop impedance – Zs values have been adjusted,
based on 230V nominal and this has slightly reduced these, for example for
32amp type ‘B’ MCB protection the maximum permitted is 1.44ohms and was
previously 1.5ohms.
Selection and erection of wiring systems – chapter 52.
• An important new regulation that particularly affects domestic and similar
installations, requires cables that are buried less than 50mm into a wall or
partition and are not enclosed in earthed metallic covering or have mechanical
protection capable of resisting nails or screws to be protected by a 30 mA
RCD as well as being installed in the ‘safe zones’ created by the position of
accessories etc. as previously permitted.
• Similarly, irrespective of depth of cable, cables that are installed in metal framed
walls require 30 mA RCD protection if not otherwise protected by earthed
metallic covering.
• The above requirements do not apply to installations that are under the control
of skilled or instructed persons, such as office buildings, large retail outlets and
industrial premises.
• Maximum permitted volt drop where supplied directly from a public
distribution system is now 3% for lighting and 5% for all other applications.

Part P of the Building Regulations

Part P came into effect in England and Wales on the 1st January 2005. It is now a legal requirement for all work on fixed electrical installations in dwellings and associated buildings to comply with relevant standards. The relevant UK standard is BS 7671: 2008, 'Requirements for electrical installations' (The IEE Wiring Regulations 17th Edition). BS 7671 covers requirements for design, installation, inspection, testing, verification and certification.

To what types of electrical work does Part P apply?
• In a dwelling
•
• In the common parts of buildings serving one or more dwellings, but excluding power supplies to lifts
•
• In a building that receives its electricity from a source located within or shared with a dwelling, and
•
• In a garden or in or on land associate with a building where the electricity supply is from a source located within or shared with a dwelling
•

The term dwelling includes houses, maisonettes and flats. It also apply to electrical installations in business premises that share an electricity supply with dwellings, such as shops and public houses with a flat above.

The common parts of buildings includes access areas in blocks of flats such as hallways and shared amenities in blocks of flats such as laundries and gymnasiums.

Part P applies to electrical installations located in outbuildings such as detached garages, sheds and greenhouses.

Part P applies to parts of electrical installations located on land around dwellings such as garden lighting.

Part P applies to electrical installations that operate at voltages not exceeding 1000 V a.c.

Notifiable work includes new installations, house re-wires, and the installation

of new circuits. Notifiable work also includes additions to existing circuits in kitchens, bathrooms, outdoors and in other special locations. (See below ).
Will all electrical work need Building Regulations approval?
No. In general, notification will need to be given to, or full plans deposited with, a building control body only if the work is major involving one or more complete new circuits, and is not being carried out by an electrical contractor registered with an authorised competent person self-certification scheme.
What types of electrical work are 'non-notifiable'?

The following types of work are non-notifiable:
• Replacing accessories such as socket-outlets, control switches and ceiling roses
•
• Replacing the cable for a single circuit only, where damaged, for example, by fire, rodent or impact (note a)
•
• Re-fixing or replacing the enclosures of existing installation components (note b)
•
• Providing mechanical protection to existing fixed installations (note c)
•
• Work that is not in a kitchen or special location and does not involve a special installation (note d) and consists of:
•
• Adding lighting points (light fittings and switches) to an existing circuit (note e)
•
• Adding socket-outlets and fused spurs to an existing ring or radial circuit (note e)
•
• Installing or upgrading main or supplementary equipotential bonding (note f)
•

Notes:

(a) On condition that the replacement cable has the same current-carrying capacity, follows the same route and does not serve more than one sub-circuit through a distribution board

(b) If the circuit's protective measures are unaffected

(c) If the circuit's protective measures and current-carrying capacity of conductors are unaffected by increased thermal insulation

(d) Special locations and installations are listed below

(e) Only if the existing circuit protective device is suitable and provides protection for the modified circuit, and other relevant safety provisions are satisfactory

(f) Such work shall comply with other applicable legislation, such as the Gas Safety (Installation and Use) Regulations
Special locations and installations
• Locations containing a bath tub or shower basin
•
• Swimming pools or paddling pools
•
• Hot air saunas
•
• Electric floor or ceiling heating systems
•
• Garden lighting or power installations
•
• Solar photovoltaic (PV) power supply systems
•
• Small scale generators such as microCHP
•
• Extra-low voltage lighting installations, other than pre-assembled, CE-marked lighting sets
•

What are competent person self-certification schemes?

Electrical contractors who register with a competent person self-certification scheme will be able to self-certify compliance with the Building Regulations whenever they carry out 'notifiable' work. Persons who are not registered with a self-certification scheme - including DIYers - will need to notify or submit plans to a building control body, unless the work is non-notifiable as described above.

How many electrical self-certification schemes have been approved?

On the recommendation of BRAC (the Building Regulations Advisory Committee), the Government has approved schemes to be operated by:
• BRE Certification Limited
•
• BSI - British Standards Institution
•
• ELECSA Limited
•
• NAPIT Certification Ltd
•
• NICEIC Certification Services Limited
•

 

[amberleaf]

With a TT- Function ,
a Test Current of 15mA or less is applied between Line – Earth ,
It enable Loop Measurement without Tripping most RCDs 30mA : * ( your also checking the sensitivity of the RCD ) -&- 3291-10

RCD Test can be Selected :
Selector , from Either the Positive ( Oº ) or from ,
The Negative ( 180º ) half-Cycle of Voltage ,
At Both Polarity Test Minimum ( best ) and Maximum ( Worst ) Trip Times :

For TN- systems the Earth Fault Loop Impedance is the sum of the following Impedances :
Impedance of the power transformer secondary winding :
Impedance of the phase conductor from the power transformer to the location of the fault.:
Impedance of the protective conductor from the fault location to the power transformer :


If an electrical installation is protected by over-current protective devices including circuit breakers or fuses,
the earth Loop Impedance should be Measured In the event of a fault the earth fault Loop Impedance should be
low enough (and the prospective fault current high enough) to allow automatic disconnection of the electrical supply by the
circuit protection device within a prescribed time interval Every circuit must be tested to ensure that the earth fault Loop Impedance value does Not exceed that specified or appropriate for the over-current protective device installed in the circuit :

Tester takes a current from the supply and measures the difference between the unloaded and loaded supply voltages. From this
difference it is possible to calculate the Loop résistance
For a TT system the earth fault Loop Impedance is the sum of the following impedances
▲ Impedance of the power transformer secondary winding
▲ Impedance of the phase conductor resistance from the power transformer to the location of the fault
▲ The Impedance of the protective conductor from the fault location to the earth system
▲ Resistance of the local earth system (R).
▲ Resistance of the power transformer earth system (Re)

The figure below shows in marked line the Fault Loop Impedance for TT system.
When the protective device is a residual device ( RCD ), Ia is the rated residual operating current I∆n . For example in a TT system protected by an RCD the maximum RA values are as follows:

Rated residual
Operating ………. 10 ………. 30 ………. 100 ………. 300 ………. 500 ………. 1000
current IΔn mA
Ra (at 50V) Ω …. 50000Ω …. 1667Ω …... 500Ω …… 167Ω ………100Ω ………. 50Ω

For this example the maximum value is 1667Ω , the Loop tester
reads 12.74Ω and consequently the condition RA is 50 / Ia is met. It also important to test the operation of the RCD using a
dedicated RCD tester in accordance with the international standard IEC60364 for a TN system :

The following condition shall be fulfilled for each circuit Zs – Uo / Ia where Zs is the earth fault Loop Impedance voltage is the
nominal voltage between phase and earth and ( Ia ) is the current that causes the automatic disconnection of the protective device
within the time stated in the following table :

Note:
▲When the protective device is a residual current device( RCD ),
Ia is the rated residual operating current I∆n , For instance in a TN system with a nominal mains voltage of
Uo = 230V protected by type gG fuses the ( Ia ) and maximum Zs values could be :

Principles of the measurement of line :
Impedance and prospective short circuit current Line Impedance on a single phase system is the Impedance measured between phase and neutral terminals. Measurement principles for line impedance are exactly the same as for earth fault Loop impedance measurement with the exception that the measurement is carried out between phase and neutral :

The protective short circuit or fault current at any point within an electrical installation is the current that would flow in the
circuit if no circuit protection operated and a complete (very low impedance ) short circuit occurred
The value of this fault current is determined by the supply voltage and the impedance of the path taken by the fault current
Measurement of prospective short circuit current can be used to check that the protective devices within the system will operate
within safety limits and in accordance with the safe design of the installation. The breaking current capacity of any installed
protective device should be always higher than the prospective short circuit current :

If the prospective fault current is measured , its value must be higher than the ( Ia ) value of the protective device concerned

* The maximum value of Zs for this example is 2.70Ω (16 amp gG fuse, 0.4 seconds). The Loop tester reads 1.14Ω and consequently
the condition Zs Uo / Ia is met :

Accordance with the International Standard IEC 60364 , for a TT system the following condition shall be fulfilled for each circuit
RA must be 50 / Ia
Where ;
RA is the sum of the resistances of the local earth system :
R and the protective conductor connecting it to the exposed :
Conductor part. 50V is the maximum voltage limit ( it May be 25V in certain circumstances ).
( Ia ) is the value of current that causes automatic disconnection : of the protective device within 0.1 seconds

Principles of RCD Measurement :
The RCD tester is connected between phase and protective on the load side of the RCD after disconnecting the load.
A precisely measured current for a carefully timed period is drawn from the phase and returns via the earth, thus tripping the
device. The instrument measures and displays the exact time taken for the circuit to be opened ,
An RCD is a switching device designed for breaking currents when the residual current attains a specific value It works on the
basis of current difference between phase currents flowing to different loads and returning current flowing through the neutral
conductor (for a single-phase installation). In the case where the current difference is higher than the RCD tripping current, the
device will trip and disconnect the supply from the current There are two parameters for RCDs; the first due to the shape
of the residual current wave form (types AC and A) and the second due to the tripping time (types G and S). A typical RCD is AC-G.
▲ RCD type AC will trip when presented with residual sinusoidal alternating currents whether applied suddenly or slowly
rising. This type is the most frequently used on electrical installations :
▲ RCD type A will trip when presented with residual sinusoidal alternating currents (similar to type AC) and residual pulsating direct currents (DC) whether suddenly applied or slowly rising. This type of RCD is not commonly used at present, however, it is
increasing in popularity and is required by the local regulations in some countries
▲ RCD type G. In this case G stands for general type (without trip-out time delay) and is for general use and applications
▲ RCD type S where S stands for selective type (with trip- out time delay).This type of RCD is specifically designed for


Auto Ramp : Check your RCD settings , 1 x / 5 x ,
The RCD should trip. Check Trip Out Current.
(1) Press the 0°/180°switch to change the phase and repeat step

Heres the Good New,s Chaps , am doing my 2392-10 on Friday 23/ 10/ 09
Am OFF the Air for One Week , I’ve left you some things to be going on with , PS kicking A--- Amberleaf
am in Manchester ,
PS, this could be a 6-pack ? on Friday