Re-take - Useful Information for 2394 :

[amberleaf]

For-Simplicity: ( L/N together ) as One , linked-together as the Regulations tells us L/N . & E

Between Live-conductors and Earth .

Minimum-insulation-résistance between Live-conductors , tested at 500V d.c. should not be less than 1MΩ .

Thismethod can be employed on a , periodic-test where installed-equipment is vulnerable to damage by thetest-voltage .

Main-switch in the On - position and all circuit-breakers closed .

• Between Live-conductor(s) separate - L . N . on there own .
Toensure that the readings obtained are , Accurate and therefore a true-reflection , of the condition of the conductors under-test .

 

[amberleaf]

From Old-Notes , not for exam purposes . Useful-Junk

Verification of Test-Results :

Itis a common-mistake for electricians to compare-test-results directly against those in BS-7671:2008

Themeasured-values of ( Zs ) of each final or distribution-circuit has to be in compliance , the obtained-values have to be compared against :

- Rule of thumb figures .
- Tabulated-values in Table . 41.2 . 41.3 . 41.4 . in BS-7671:2008 , these-values will have to be corrected for temperature . Or
- Table provided in Guidance-Note 3 .
- The Earth-fault-loop-impedance-values , provided by the designer .

Rule of Thumb-Figures : ( 0.8- 80%)

(Zs ) value at the remote-end of a circuit should not exceed ( 0.8 ) of the a appropriate-value inBS-7671

A Note-under Tables 41.2 . 41.3 . 41.4 . 41.6. States that
“ the circuit-loop-impedance ( Zs ) given in the tables should not be exceeded when theconductors are at their normal-operating-temperature , if the cables are at a different-temperature when tested “ the reading should be adjusted accordingly, see - Appendix14 .

Therequirements are satisfied if the , Measured ( Zs ≤ 0.8 x Uo / Ia ) i.e. 80% ofthe tabulated-values in BS-7671:2008

Determine whether the measured-values of earth-loop-impedance foreach-circuit satisfy the requirements of BS-7671:2008

Shower-circuit: BS-7671:2008 earth-loop-impedance Ω - 0.62 x 0.8 = 0.49 : Measured-value Ω - 0.50 : Pass or Fail .
Ring-final-circuit: BS-7671:2008 earth-loop-impedance Ω - 1.14 x 0.8 = 0.91 : Measured-value Ω - 0.84 : Pass or Fail .
Radial-sockets: BS-7671:2008 earth-loop-impedance Ω - 1.85 x 0.8 = 1.48 : Measured-value Ω - 1.36 : Pass or Fail .
Immersion-heater: BS-7671:2008 earth-loop-impedance Ω - 2.67 x 0.8 = 2.13: Measured-value Ω - 1.36 : Pass or Fail .
Lights- ( 1[SUP]st[/SUP] floor ) : BS-7671:2008 earth-loop-impedance Ω - 18.5 x 0.8 = 14.8: Measured-value Ω - 13.9 : Pass or Fail .
Lights- ( Gnd floor ) : BS-7671:2008 earth-loop-impedance Ω - 10.0 x 0.8 = 8.0: Measured-value Ω - 0.74 : Pass or Fail .

 

[amberleaf]

From Old-Notes , not for exam purposes. Useful-Junk

Verification of Test-Results :

It is a common-mistake for electricians tocompare-test-results directly against those in BS-7671:2008

The measured-values of ( Zs ) of each final ordistribution-circuit has to be in compliance , the obtained-values have to becompared against :

Tabulated-values in Tables - 41.2 . 41.4 . in BS-7671-2008 .

Two-factors , bothinvolving-temperature , must be taken into account when comparing any measured-value of ( Zs ) with the values obtained form BS-7671 :


i) Cable-operating-temperature-factor ( Assumed to be 70°C ) &
ii) The actual-temperature of theconductors when the measurement was taken , ( Usually-deemed to be the Ambient-temperature )

Conductor-operating-temperature-factor
The tabulated-value in BS-7671: are used for design-purposes and assume that the cables are attheir maximum-operating-temperature .

i.e. 70°C for thermoplastic - PVC/PVC . cables .

for comparison-purposes with BS-7671: the ambient-temperature at the time of the test is assumed to be 20°C .

i.e. using the temperature-coefficient of résistance for copper of , 0.004Ω/°C , then the factor to adjust the measured-loop-résistance-value to what it would be at 70°C .

= 1 + [ 50 x 0.004Ω/°C ] = 1.2 . for PVC - insulated-cables .

This factor is applied as a , multiplying-factor to be measured ( Zs - value ) then compared against the tabulated-value in BS-7671:2008:
Alternatively - the 1.2 can be used a divisor and applied directly to the tabulated-value in , BS-7671:2008: The measured-value can then be compared directly against this reduced-value .

Example : Determine whether the measurement taken at the socket-out for thecircuit shown complies with BS-7671:2008:

[ Table 41.3. type-B . BS-EN-60898 - 32A = 1.44Ω ] three-sockets , reading furthest-socket - ( 1.1Ω )

Using the method stated : Measured-value , x 1.2 = 1.1 x 1.2 = ( 1.32Ω )

Note : therefore , as the adjusted-measurement is less than , 1.44Ω it complies .

 

[amberleaf]

From-old-notes . 2008 .

Actual-conductor-temperature-factor

If themeasured-earth-fault-loop-Impedance-value , is taken at ambient-temperature Other than 20°C then it must be adjusted for the temperature-difference .

Example : Determine whether the measurement taken at the socket-outlet for thecircuit show-complies with BS-7671:2008:

32A -BS-EN-60898 Maximum- Zs 1.44Ω -

The ( 1.3Ω ) reading on the instrument has been Obtained at an , Ambient-temperature = 25°C .

Using the temperature-coefficient of résistance for copper of , 0.004Ω/°C , thenthe factor to adjust the measured-loop-résistance-value to what it would be at , 70°C

= 1 + [ ( 70 - 25) x 0.004Ω/°C ]
= 1 + [ 45 x 0.004Ω/°C ] = 1.18

From the table-provided :

Therefore , Reading at 70°C = 1.30 x 1.18 = 1.53Ω

As the measurement taken is greater than 1.44Ω then the circuit Does-Not-Comply .

Where the designer has provided test-values , they should have been compensated for the temperature-differences, thus enabling the Inspector to make a direct-comparison .

 

[amberleaf]

Earth-fault-loop-impedance:

State : four-points as described in Guidance-Note - 3 , where the measurement of earth-fault-loop-impedance is required to be taken .

i) at the supply-intake - ( Ze )
ii) at each distribution-board - ( Zdb ) GN-3
iii) at theremote-end of all finial-circuits - ( Zs)
iv) at each-socket-outlet - ( Zs )

indentify from the Four-points indentified above , reasons why these measurements are necessary .

i) at the supply-intake .

- to ensure the installation is effectively connected to Earth . -&-s big-time . 2394.
- to confirm that the actual ( Ze ) is equal to or less than what the designer has used in his design-calculations .

ii) at each-distribution-board ( Zdb )
- to enable the , prospective-earth-fault-current to be calculated .
- to confirm that the , protective-device supplying the distribution-board under earth-fault-conditions in thetime required by BS-7671:2011:
- in conjunction with either a visual-inspection , an ( Ra ) or a ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )test , an earth--loop-impedance-test will confirm-polarity .

iii) at the remote-end of all-final-circuits ( Zs )
- to confirm that the protective-device supplying the final-circuit-disconnects under-earth-fault-conditions inthe time required by BS-7671:2011:

iv) at each-socket-outlet .
- to confirm that the protective-device supplying the socket-outlets disconnects under-earth-fault-conditions inthe time required by BS-7671:2011:

Identify ,Two-factors that the Inspector will have to consider when confirming his ,earth-fault-loop-impedance-measurements , are in compliance with the requirements of BS-7671:2011:

i) the normal-operating-temperature of the cables .
ii) the temperature of the cables at the time of test .

typical :electrical-installation(s) require an effective-connection to earth as part of the protective-system .

identify the Three most common , earthing-systems available to the District-Network-Organiser - ( DNO ) and state the , maximum-earthing-fault-loop-impedance at the supply-terminals for each-system .

i) TN-S . 0.80Ω
ii) TN-C-S . 0.35Ω
iii) TT - . 21Ω , from the DNO suppliers earth-electrode - Only . 21Ω + the consumers electrode-résistance .

you have an independent - earth-electrode - Ω , from the-supplier

iii) TT - . 21Ω , O.S.G. p.11
TT - arrangement ,21Ω is the usual-stated-maximum-résistance of the distributions , earth-electrode at the supply-transformer . Etc .

Note: the résistance of the ( Consumers-installation-earth-electrode ) should be as low as practicable and a value exceeding 200Ω may not be stable .

Type of Protective-device : p.23 -O.S.G. RCBO - it can serve , under-fault-conditions . Overload : Short-circuit : Earth-fault. written-exams.

30mA RCD - is for Additional-protection only , theprotect the User . so its Additional . :gettree:

 

[amberleaf]

Values of (R1+R2) are measured :gettree:
Using an ohmmeter with a low range, such as 0to 20Ω, having a no-load voltage of between 4 V and 24 V, d.c. or a.c., and a short-circuit current ofnot less than 200mA (Regulation612.2.1 refers). The Q/A came up on the 2391 .

 

[amberleaf]

2394 : Written-exams .

Additional-protection:

Additional-protection by Residual-current-devices.

Theuse of an RCD whose rating ( IΔn ) does not exceed 30mA and disconnects within 40mS when tested at 5 x ( IΔn )

Is recognised as providing :

• Additional-protection against the failure of Basic-protection .
• Additional-protection against the failure of Fault-protection .
• Additional-protection against Carelessness by the User .

RCD-tester, must comply with BS-EN-61557-6
Leads to be in compliance with - GS-38

 

[amberleaf]

( G) non-delay RCD :

Q) for a 100mA non-delay RCD toBS-EN-61009-1 the residual-currents and maximum-permitted-disconnection-times , are .

a) 100mA - 300mS : 500mA - 40mS
b) 100mA - 130mS : 1500mA - 150mS
c) 100mA - 0mS : 100mA - 40mS
d) 100mA - 400mS : 500mA - 50mS

Q) The protective-measure , automatic-disconnection of supply . ( G) non-delay RCD :
a) is only permitted if the installation is under effective-supervision .
b) is a method of reducing thermal-effects .
c) is acombination of basic and fault-protection .
d) is a combinationof under and over-voltage-protection .

Q) An earth-fault-loop-impedance-test determines the actual-value of : a) Zs , b) Ze , c) R[SUP]1 [/SUP], d) R[SUP]2 [/SUP], The word - external was not Used . :gettree:

Earth fault loop impedance (Zs) is a characteristic vitalto the protective measure Automatic Disconnection of Supply (ADS),

The meaning of earth fault loop impedance
Earth-fault-loop-impedance (Zs) is theimpedance of the intended path of an earth fault current ( known as the earthfault loop )

 

[amberleaf]

GN-3p.66 . Requirements for Inspection & Testing .

Written-exams .
Q) What is the reason for a periodic-inspection. ? :christmaswreath:

3.8.1. Scope :
Thepurpose of periodic-inspection and testing is to provide an engineering-view on whether or not the installation is in asatisfactory-condition where it can continue to be used in a safe-way .

The periodic-inspectionand test-comprises a detailed-examination of the installation together with appropriate-tests .
The inspection is carried out without taking-apart or dismantling-equipment as far as is possible .

GN-3 are reminding us .
The tests made are mainly to confirm that thedisconnection-times-stated in Chapter -41 . are met , as well as highlighting-other-defects. Etc .

Q) On completionof periodic-testing an old-domestic-installation , theinsulation-résistance is found to belowthe requirements of BS-7671:2011: The immediate-action to be taken is to . ?

Notify thelocal-supply-authority
Notify the person-ordering the work
Put awarning-notice on the supply-intake-position
Protect thecircuits with smaller-sizes of fuses

Q) The Electricity at Work-Regulations 1989 concern’s its self with . ?
All aspects of electrical-systems
System up to 1000 volts
Special-locations only
High-voltage-systems only

2392-10 - 2394 :
Q) it is important to test a new-installation in the correct-sequence because . ?
The sequence is stated in GN-3
Each test relies on the previous to be correct
It is more-convenient
It is easy to remember

 

[amberleaf]

Old-notes 2002

Insulation-résistance, By calculations .

An installation comprising six-circuits have individual-insulation-résistance of : 2.5MΩ . 8MΩ . 200MΩ . 200MΩ . 200MΩ . 200MΩ.

Q ) So thetotal insulation-résistance will be .

1/Rt = 1/2.5 + 1/8 + 1/200 + 1/200 + 1/200 + 1/200 .

= 0.4 + 0.125 + 0.005 + 0.005 + 0.005 + 0.005 .

= 0.545

Rt = 1/0.545

= 1.83MΩ …… 1.0MΩ minimum but less than 2MΩ . ◄◄

This is clearly greater than the 1.0MΩ minimum butless than 2MΩ .

lessthan 2MΩ . ) are recorded then this might indicate a latent but not yet visible-fault in the installation. which would require further-investigation .

• If a value of less than 2MΩ is recorded it may indicate a situation where a fault isdeveloping .

Themore-resistances , there are in parallel, the lower the overall-résistance ,and in consequence , the longer a cable the lower the Insulation-résistance
Addto this the fact that almost all installation-circuits are also wired in parallel

 

[amberleaf]

this is the Question your likelyto get . 2392-10 / 2394.

Q) if each of the three-circuits had been tested individually and gave readings of - 80MΩ , 60MΩ , & 30MΩ respectively , what would be the expected overall insulation-résistance .

80MΩ , 60MΩ , 30MΩ ,

Q ) So thetotal insulation-résistance will be .
1/Rt = 1/80 + 1/60 + 1/30 .

= 0.0125 + 0.0166 + 0.033

= 0.0621 .

Rt = 1/ 0.621 = 16. , doingyour Calculation . where your decimal-point here . Yeah


a) 0.0625MΩ
b) 15MΩ
c) 16MΩ
d) 160MΩ

 

[amberleaf]

Q) the metal-partsof an building-structure are called : ? conductive-part liableto introduce a potential
earthing.
equipotential-bonding
exposed-conductive-parts
extraneous-conductive-parts

Regulations- p.28 .
Extraneous-conductive-parts A conductive-part liable tointroduce a potential , generally Earth-potential , and notforming part of the electrical-installation.

Q) the metal-parts of an electrical-installation notnormally-live are called : ?
earthing.
equipotential-bonding
exposed-conductive-parts
extraneous-conductive-parts

Regulations- p.27 .
Exposed-conductive-part Conductive-part of equipment which can be touched & which is notnormally-live , but which canbecome-live-under-fault-conditions .

Q) the process which maintains a potentialof zero-volts between all extraneous-exposed-conductive-parts is called : ?
earthing.
equipotential-bonding
exposed-conductive-parts
extraneous-conductive-parts

Q) the act of connecting exposed-conductive-parts to the earthing-terminal ofan installation is called : ?
earthing .
equipotential-bonding
exposed-conductive-parts
extraneous-conductive-parts

Q) the trunking & conduit of an electrical-installation are called : ?
thegeneral-mass of earth
thecircuit-protective-conductor - ( CPC)
exposed-conductive-parts
extraneous-conductive-parts

Exposed-conductive-part Conductive-part of equipment which can be touched & which is notnormally-live , but which canbecome-live-under-fault-conditions .

Q) an electrical-connectionwhich maintains exposed-conductive-parts & extraneous-conductive-parts atthe same-potential is called : ?
(CPC ) - circuit-protective-conductor
earth-conductors
protective-equipotential-bonding : equipotential-bonding for thepurposes of safety .
supplementary-bonding

 

[amberleaf]

Re-cap. 2392-10 , 2394.

Résistance in Series :

These are resistance joined , end to end in the form of a chain .

The total-resistance-increases as more-resistances are added .

Hence: if a cable-length is increased , its résistance will increase in proportion .

Example: 100m length of conductor has twice the résistance of a 50m length of the same-diameter .

1/R[SUP] total [/SUP] = 1/R[SUP]1[/SUP] + 1/R [SUP]2[/SUP]+ 1/R[SUP]3[/SUP] + 1/R[SUP]4 [/SUP]

1Ω - ( R[SUP]1[/SUP]) 2Ω - ( R[SUP]2[/SUP]) 10Ω - ( R[SUP]3[/SUP]) 4Ω - ( R[SUP]4[/SUP] ) Ω .

R[SUP] total [/SUP] = 1 + 2 + 10 + 4 = 17Ω

Résistance in parallel .

These are résistance joined like therungs of a ladder . here the total-résistance-decreases .

1/R[SUP] total [/SUP] = 1/R[SUP]1[/SUP] + 1/R [SUP]2[/SUP] + 1/R[SUP]3[/SUP] + 1/R[SUP]4 [/SUP]
[SUP] [/SUP]
3Ω - 6Ω - 8Ω - 2Ω

1/R[SUP] total [/SUP] = 1/R[SUP]1[/SUP] + 1/R [SUP]2[/SUP] + 1/R[SUP]3 [/SUP] + 1/R[SUP]4 [/SUP]

= 1/3 + 1/6 + 1/8 + 1/2

= 0.333 + 1.167 + 1.125 + 0.5

Therefore: = 1/1.125 .

High-value-resistances’ inparallel . hence : anincrease in cable-length-results in a decrease in insulation-résistance.

This value is measured in millions of ohms . - megohms ( MΩ )

Watch you Questions shown in words . :mad2:

• If youthen do the full-calculation using the ( Un-round up figures ) 1.125 .
• In exams , you will have to ( Roundit up ) exactly 16M . 100M .

 

[amberleaf]

BS-7671:2008/ 2011: Basic principles of : Protection against !!

Protection against Electric-Shock . Part-4 . ( So in theory , Principles of Electric-Shock protection )

Electric-Shock occurs when a person becomes a part of the electrical-circuit .

Methodsused , keep-people away from Live-electrical-equipment. it is called - Basic-Protection . 131.2.1.

► Consumer-Unit , ( 2392-10 . Why do we use Class - 11 enclosure on all Installations now . Protection for the User ) N/A, Touching exposed-conductive-parts .

Basic-Protection . Protection against Electric-Shock. under fault-free-conditions .

By- Definition : p.23. Basic-Protection.
Note : for low-voltage-installations , systemand equipment , basic-protection generally-corresponds to ( Protection against ) direct-contact, that is

“ contact of persons or livestock with live-parts “

Re-cap: Indirect-contact:
Touching exposed-conductive-parts , such as themetal-work of an appliance . whichhas become live as a result of a fault . The potential-voltage on this metalwork rises above earth-potential , electric-shock may occur when someone-touches the metalwork .

By- Definition : p.28. Fault-Protection.
Note : for low-voltage-installations , systems and equipment , fault-protection generally corresponds to ( Protection against ) indirect-contact. mainly with regards to failure of ,basic-insulation ,

Indirect-contactis , “ contact of persons or livestock with exposed-conductive-parts which have become-live under fault-conditions “

Protection against touching something made live as a result of a fault , is called fault-protection , and is achieved by protective-equipotential-bonding & automatic-disconnection of the supply - ( ADS ) in the event of a fault-occurring , 131.2.2.

O.S.G. p23 . Types of protective-device .

RCBOs- will minimize-inconvenience in theevent of a fault and is applicable toall systems , TN-S , TT -
Theconsumer-unit contains devices for the protection of final-circuit(s) against : Overload , Short-circuit , Earth-fault . ( Electronic to trip the contacts )

RCBO- Small-white-flylead which connect to Earth , either D.C.. sensing or A.C. sensing .
Modern - RCBOs have a cream-wire which connects to earth known as a functional-earth .
Modern - RCBOs some - facts , generally the ones with a functional-earth use ( Electronic to trip the contacts ) as Opposed to just using ( Coils )

RCD- is used to provide Additional-protection, against electric-shock and the earthing-system is there to keep all ( Exposed / Extraneous-conductive-parts - ( Surfaces ) at or about the same-potential in the event of a fault , & to clear the fault-quickly byoperating the Protective-device .

Protective-device(s) Genetic-name for : :gettree: :17:
Fuse .
Circuit-breaker .
RCD . to improve-safety .
RCBO - MCB /RCD .

 

[amberleaf]

Protective-equipotential-bonding

Is equipotential-bonding for the purpose of safety , theapplication of protective-equipotential-bonding to earth is one of theimportant-principles for safety .
Regulation- 131.2.2.

p.17. inconnection with fault-protection , theapplication of the method of protective-equipotential-bonding isone of the important-principles for safety . :santa5:

 

[amberleaf]

Re-cap:

The is the nearest I canget to Q/As about , Safe-Isolation.

Q) To verify or prove a successful-electrical-isolationyou would use a ? Voltage-indicator
Voltage-indicator
Voltage-proving-unit
Set of GS-38 test-leads
Small-padlock.

Q) To securean electrical-isolation you should use a ? padlock .
Voltage-indicator
Voltage-proving-unit
Set of GS-38 test-leads
padlock .

Q) Where a test-instrument or voltage-indicator is used to prove a supply-dead , thesame-device must be tested to show that it still-works using a ? Voltage-proving-unit
Voltage-indicator
Voltage-proving-unit
Set of GS-38 test-leads
Small-padlock.

Q) To give adequate-protection to theperson carrying-out a safe-isolation-procedure , thetest-instrument must incorporate a ? Set of GS-38 test-leads
Voltage-indicator
Voltage-proving-unit
Set of GS-38 test-leads
padlock.

Q) When connecting single-phase-loads to a three-phase-supply , we must take care to distribute the single-phase-loads equallyacross the three-phases so that each phase carries approximately the same-currents , this is called ? Balancing of theload .

Re-cap: Socket-outlets. 2392-10

Additional - 30mA RCD protection is required for socket-outlets .
Ifused by Ordinary-persons .
And intended for general-use

Regulations - 411.3.1. 415.1.1.

Additional protection for socket-outlets . RCD / Circuit-breaker .

Additional-protection by 30mA RCD is required in ( Addition ) to ( Overcurrent-protection ) for allsocket-outlets to be used by Ordinary-persons and intended for general-use .

For this reason . Additional protection
Is provided in case ( Basic-protection ) or ( Fault-protection-fails ) or if the User of the installation is careless - 415.1.1.

By definition . Ordinary-person : A person who is neither a skilled-person nor an instructed-person .

 

[amberleaf]

Q) Continuity of protective-conductors .

Recap -Written exams . 2394

What is you reason for this .
The object of the test is to ensure that every-circuit-protective-conductor is correctly-connected and has avery-low-résistance .

Q) Insulation-résistance - ( IR )

What is you reason for this .
The object of the test is the verify the quality of theinsulation and that the insulation-résistance has a high-value . MΩ

The test is made at the consumer-unit with the supply-disconnected using an insulation-résistance-tester which supplies a voltage of 500V . ( BS-EN-61557-6 )

Q) Part - 6 of the IET - Regulations deals with ?
Protection for safety
Selection and erection of equipment
Special-installations
Inspection & testing .

Q) the electricity-supply to adomestic-consumer is usually protected at the incoming-service-position by a ?
Meter
Double-pole-switch
100A circuit-breaker
100A HBC - fuse . ( BS-88-3 - C )

Q) What action is necessary toproduce a secure-electrical-isolation ? The isolated-supply must be locked-off or secured with a padlock
Isolate the supply and observe that thevoltage-indicator-reads-zero
Find connect a test-device such as a voltage-indicator to the supply
Larger-pieces of equipment may require-isolating at a local-isolator-switch
The isolated-supply must be locked-off or secured with a padlock

 

[amberleaf]

My- point .

The form of protection-provided by the Insulation of Live-parts would be .
Protection against “ direct-contact “

p.23 . Basic-protection: Protection against electric-shock under fault-free-conditions .
Note : for low-voltage installations , systems andequipment . basic-protection generally-corresponds to protection against “ Direct-contact “ that is “ Contact of persons or livestock with Live-parts“

Whywas the name left in BS-7671:2008 “ Direct-contact“
“ Direct-contact“ Deleted by BS-7671:2008: ( see Basic-protection)

It was left in the BS-7671:2008:2011: for a better understanding of the meaning of the : Word “ Direct-contact “

Calculationof earth-fault-loop-impedance : ( Zs )
Themost commonly used protective-measure against ( “ Direct-contact “ Basic-protection) is that of automatic-disconnection of the supply , using the overcurrent-protective-device

Which also provides protection against overload & / or short-circuit-currents for the circuits-concerned .

Residual-current-devices ( RCD ) or combined-devices ( RCBOs ) RCD / Circuit-breaker . ( inExams use the full-name , Not MCB )

Whichever type of device is chosen , it is necessary for the designer to calculate the earth-loop-impedance ( Zs ) of every-circuit in the installation .
Tocheck that these impedances do not exceed the maximum specified in BS-7671:2008:2011: Tables, 41.4. 41.5 . Etc .

The earth-loop-impedance thathas to be considered is that which comprises the impedance of the source , the Line-conductor up to the fault plus the protective-conductor from the fault to the source , Note : that when an RCD or RCBO is used to provide automatic-disconnection of the supply in a TN- system , the calculations of ( Zs ) is normally unnecessary-provided that continuity of the earth-loop hasbeen established .

Regulation: p.55 . look at 411.4.7. / 411.3.2.3. , the values specifiedin Table - 41.3 for the types and ratings of overcurrent-devices listed may be used instead of calculations . 2392-10. your off the hook here . RCBOs or Circuit-breakers .

Where a circuit-breaker is used tosatisfy the requirements of Regulation , Etc. Uo of 230Vand disconnection-time of 0.4s in accordance with Regulation - 411.3.2.2. or 5s in accordance with Regulation - 411.3.2.3. the values specified in Table - 41.3 for the types andratings of overcurrent-devices listed may be used instead of calculations .

Re-cap: 2392-10 . ( RCBOs ) RCD / Circuit-breaker / Overcurrent-protective-device.

You will not get this in your Exams . 2392-10, just an understanding . Yeah .
Theother , reason for calculating the earth-loop-impedances is to check that the circuit-protective-conductors areadequately-protected-thermally .
Thatthey comply with ,adiabatic-equation given inRegulation - 543.1.3. Etc .

BS-7671:1992: + Amd 1:1994 included a regulation that required account to be taken of the increase in temperature and résistance of conductors as a result of the fault-current .

However: this Regulation also allowed a simpler approach to be taken under-some-conditions , for thedevice listed in Appendix - 3 of BS-7671: 1994 , the requirement was deemed to be satisfied if the circuit-loop-impedance met the required when the conductor(s) are at there normal-operating-temperature .

Fuses to BS-88-3 - C . up to 100A . p.56. Old - BS-1361
Semi-enclosed-fuses to BS-3036 to 100A .p.56 .
Fuses to BS-88- part 2 .& Part -6 up to 100A . p.56 .
Type B . C , D , circuit-breakers , BS-EN-60898 , & RCBOS to BS-EN-61009-1 up to 125A . p.56

circuit-loop-impedance -1994 , ( Zs ) The word circuit-loop-impedance is not used 2011: Earth-fault-loop-impedance. all it does is define it a bit better . Yeah . use the full title in exams .

 

[amberleaf]

GN-3: p.39
The purpose of the insulation-résistance-test is to verify that the insulation ofconductors-provides adequate-insulation , is not damaged and thatlive-conductors or protective-conductors are ( Notshort-circuited )

Operation of two-wayand intermediate light-switch s -&-s

GN-3. p.40 / 41 .
Insulation-résistance-test of a whole-consumer-unit . ( Lamps removed for test ) Open-circuit

For circuits containing two-way-switching or two-way and intermediate-switching ,the switches must be operated oneat a time and the circuitssubjected to additional-insulation-résistance-test in these-configurations .

GN-3. p.41 .
Insulation-résistance-test of a final-circuit . ( Lamps removed for test )

Operation of two-wayand intermediate light-switch s -&-s

For circuits containing two-way-switching or two-way and intermediate-switching ,the switches must be operated oneat a time and the circuitssubjected to additional-insulation-résistance-test in these-configurations .

 

[Knobhead]

Spam.

Pitty you can't spell, a credit to you're company.

To confuse everyone, the post I was refering to has been deleted. NOT AL's posts.

 

[amberleaf]

O.S.G.p96 .

Re-cap,

For an installation-operating at 400/ 230V , although an insulation-résistance-value of only 1MΩ complies with BS-7671 :

Where.

The insulation-résistance-measured is less than 2MΩ the possibility of a latent-defect-exists .

In these circumstances , each-circuit should then be tested separately .

2394 : Keep in mind written-exams . :gettree: :17:

 

[amberleaf]

O.S.G.p87 . 2392-10 , just starting out on Inspection & Testing . Inspection meaning - Visual is our first line of defence .

One of the most important Regulations in exams , 612.1.
If any test indicates a failure to comply , that test and any preceding-test , theresults of which may have been influenced by the fault-indicated , shall berepeated after the fault has been rectified .

O.S.G. 9.3. Testing .
Testing must include relevant-tests from the following-checklist

O.S.G. 9.3.1. Testing checklist . ◄

Insulation-reading:
Test-instrument , Readings with leads . Open-circuit - > 999MΩ .

Q) if there is no British-Standard then the insulation-résistance should not be less than 1MΩ .

 

[amberleaf]

Leaning - Curve . Only. Old-Notes 2008 . :icon_bs:

From the information given determine ,

The value of the insulation-résistance-measured taken and the requirements of BS-7671: are satisfied . Your-Call . Yeah

1/Rt = 1/R1 + 1/R2 + 1/R3 + 1/R4 + 1/R5

1/Rt = 1/6 + 1/3 + 1/4 + 1/12 + 1/6

Find the lowest-common-denominator i.e. - 12

= 2 + 4 + 3 + 1 + 2 - 12 .

1/Rt = 12 / 12

Therefore : Rt/1 = 12 / 12 = 1MΩ .

Re-cap . Reminder - Guidance-Note - 3 .

Although the requirements of BS-7671: appear to have been satisfied , GN-3 refers to the possibility of a [ Latent-Defect ] existing within the installation . the circuits’ should be tested individually and a minimum-insulation-résistance of 2M is recommended .

As the measurement taken for all of the circuits are above 2MΩ then no investigation would be required .

 

[amberleaf]

Leaning - Curve . Only. Old-Notes 2008 . :icon_bs:

From the information given determine ,

The value of the insulation-résistance-measured taken and the requirements of BS-7671: are satisfied .

1/Rt = 1/R1 + 1/R2 + 1/R3 + 1/R4 + 1/R5 + 1/R6

1/Rt = 1/120 + 1/30 + 1/40 + 1/12 + 1/60 + 1/10

Find the lowest-common-denominator i.e. - 120

= 1 + 4 + 3 + 10 + 2 - 12 - + 12 - 120

1/Rt = 32 / 120

Therefore : Rt/1 = 120 / 32 = 3.75MΩ .

 

[amberleaf]

Electricians , Do I Mixor Match ??

SafeSection of Devices for Installation in Assemblies . August - 2011:

Awarning against the practice of installing devices ( E.g. RCBOs , Circuit-breakers ) of one-manufacturer into assemblies ( E.g. consumer-units . Distribution-boards ) of another-manufacturer . there is evidence that some installers aremixing-products , oftenwithout fully understanding the potential-safety-implications .

Assembliessuch as consumer-units , Distribution-boards and panelboards are tested with specific-devices installed , these devicesare more often than not from the same- manufacturer as the enclosure , testingand certification is undertaken to BS-EN-60439 . formerlyBS-5486 Although BS-5486 is now obsolete there are manyexisting-installations with assemblies complying with this standard and the issues of mixing-different-manufacturer’s devices equally apply , particularly where older-devices maybe difficult to source .

Inall cases , installing-devices other than those declared by the assembly-manufacturer invalidates any testing / certification andwarranty .

BS-7671uts specific-responsibility on the installer . Regulation - 510.3 . requires that the installer takes into account the manufacturer’s-instructions . it is therefore theresponsibility of the installer who intends to , mix-different- manufacturer’s-devices/ components . in an assembly , to undertake appropriate-testingand ensure-conformity with BS-EN-60439 . if this is not done then there is aprobability that , in the event of death . injury . fire or other-damage , the installer would be accountable under , Health & Safety - legislation .

Althoughdevices may appear similar , the dimensions . technical-performance andterminations are not necessarily-compatible .

Distributor and Wholesalerresponsibilities :

A distributor and wholesaler also has aresponsibility under the , general-product-safety-regulations to act “ withdue care “
Distributorand wholesaler should be able to substantiate any advice related to ,interchangeably of devices in assemblies , if the installer acts on a distributor’s - advice and information , andin doing so produces anon-compliant-assembly , then both the distributor and installer may be liable forany-consequences .

 

[amberleaf]

Circuit-breakers to BS-EN-60898 &RCBOs to BS-EN-61009-1 in non-preferred-current-ratings

Circuit-breakersto BS-EN-60898
RCBOsto BS-EN-61009-1 are sometimes encountered that have a rated-current other than thepreferred-values [ 3A , 6A , 10A ] listed in Table - 41.3. of BS-7671:2008:2011:

Themaximum-value of ( Zs ) for such a device , at a nominal-voltageof [ Uo - 230V ] can be found from the right-hand-columnof Table - 41.3. of BS-7671:2011:
Table- 41.3 , right gives therelevant-information .

Type - B circuit-breaker . having arated-current ( In ) of 8A ( or the overcurrent-characteristic of an8A Type - B RCBO ) the maximum-value of ( Zs )
at 230Vis 46 / In , = 46 / 8 = 5.75Ω .

Maximum( Zs ) for circuit-breakers to BS-EN-60898 and the overcurrent-characteristic of RCBOs to BS-EN-61009-1for instantaneous-operation giving compliance with the , 0.4 & 5 seconds ,disconnection-times at nominal-voltage [Uo - 230V ]

Table- 41.3.

Type- B - ( Zs ) Ohms for devices ofrated-current ( In ) 46/In .
Type- C - ( Zs ) Ohms for devices ofrated-current ( In ) 23/In.
Type- D - ( Zs ) Ohms for devices ofrated-current ( In ) 11.5/In.

Obsolete-Circuit-Breakers :
Maximum-valuesof ( Zs ) for circuit-breakers for which thisinformation is no longer given in BS-7671: can be obtained either from the edition of BS-7671: that was current when the deviceswere readily-available , or by reference to the manufacture’s - data .

Alternatively, for MCBs to BS-3871: Table - 2 , can be used to find the maximum-value of ( Zs ) at a nominal-voltage of [ Uo - 230V ]

For a Type- 2 circuit-breaker to BS-3871: having a rated-current ( In ) of 30A , the maximum-value of (Zs ) at 230V is [ 32.8 / In = 32.86/ 30 = 1.1Ω ]

Maximum( Zs ) for circuit-breakers toBS-3871: for instantaneous-operationgiving compliance with the , 0.4 & 5 seconds , disconnection-times at anominal-voltage of [ Uo - 230V ]

Type( Zs )
Type- 1 . Ohms - for device of rated-current- ( In ) 57.5/In
Type- 2 . Ohms - for device of rated-current- ( In ) 32.86/In
Type- 3 . Ohms - for device of rated-current- ( In ) 23/In
Type- 4 . Ohms - for device of rated-current- ( In ) 4.6/In

Type- B - ( Zs ) Ohms for devices of rated-current ( In ) 46/In .
Type- C - ( Zs ) Ohms for devices of rated-current ( In ) 23/In .
Type- D - ( Zs ) Ohms for devices of rated-current ( In ) 11.5/In .

Obsolete-fuses :
Maximum-valuesof ( Zs ) for fuses for which this information is no longer given in BS-7671: can be obtained either from the editionof BS-7671: that was current when the deviceswere readily-available , or by reference to the manufacture’s - data .

After 31 - December 2011 : one of these approaches is necessary forfuses to BS-88-2.2. : BS-88-6 : and BS-3871 : as data for them is notincluded in , BS-7671:2008:incorporating Amendment - 1 . 2011:

Overcurrent-protective-devices generally :
Forany type and rated-current of a fuse or overcurrent-circuit-breaker , includingall those mentioned above , the maximum-value of ( Zs ) can be found using the , formula given in Appendix - 3 of BS-7671: Where :- Zs = Uo /Ia .

Uo- is the nominal A.C. r/ms line-voltage to Earth - 230V.
Ia - is the current causing-operation of the protective-devicewithin the specified-time . such as 0.4 or 5 seconds . obtained fromthe manufactures - time / current-characteristics for the particular device-type and rating .

Supposed the manufactures - time / current-characteristic for a 400A - fuse , to BS-88-2.1. gives a value of ( Ia of 2840A ) for a disconnection-time of 5 - seconds . Using the above - formula , the maximum-value of ( Zs ) for the fuse , fordisconnection-time of 5 - seconds and anominal-voltage
( Uo ) of 230V , 230V ÷ 2840A = 0.08Ω

Measured- values of ( Zs ) taking account of conductor -temperature

It should not be forgotten that when comparing ameasured-valued of ( Zs ) with the maximum-value of ( Zs ) allowable for the device used for , fault-protection , account must betaken of the temperature and résistanceof the circuit-conductors . Appendix - 14 of BS-7671: refer .

Provethat the following table-provides instantaneous-disconnection for a BS-EN-60898 & BS-EN-61009-1 - Type B .32A Circuit--breaker using table 41.3. App - 3 .

Zs ≤ Uo /Ia . Table- 41B2

16[SUP]th[/SUP] Edition :
Type- B . 48/In
Type- C . 24/In
Type- D . 12/In

Zs ≤ 240/ 160 = 1.5

48/ 32 = 1.5Ω
240/ 48 = 5. In
32A x 5 = 160A

Mostmanufactures data-shows 3 - 5 x . In for instantaneous-disconnection .

Zs ≤ Uo /Ia .

17[SUP]th[/SUP]Edition : 2008: 2011 :
Type- B . 46/In
Type- C . 23/In
Type- D . 11.5/In

Zs ≤ Uo /Ia . Table - 41.3.

Zs ≤ 230/ 160 = 1.4375 . Round-up to 1.44Ω
46 / 32 = 1.44Ω
230 / 46 = 5. In

Type- B : > 3/In . ≤ 5.0 / In
Type- C : > 5/In . ≤ 10.0 / In
Type- D : > 10/In . ≤ 20.0 / In


If Armoured-Cable is harshly-treated the Amour-wires canbecome-displaced , twisted or stretched , leading to bulges in the sheath-material
Cablesare uniform and circular in cross-section when manufactured , but mishandlingcan result in bulges an kinks which cancause difficulties in pulling into ducts, termination at glands , as well as being unsightly , such problems can be causedby incorrect-pulling from the drum . the introduction of loop and kinks ,pulling round too tight a bend .

 

[amberleaf]

Q) a 6A BS-EN-60898 circuit-breaker is used to protect a circuitwith a , maximum-earth-fault-loop-impedance ( Zs ) of 3.83Ω would be type ? Table - 41.3 . p56
B. ……… above 3/In up to including 5/In
C . ……… above 5/In up toincluding 10/In
D. ……… above 10/In up to including 20/In

Youcan’t predicted what level yourcircuit-breaker will trip on , will trip instantly between three and five timesits rated-current [ 3In x 6A = 18A : 5In x 6 = 30A ]
Type- B current for time , 0.1sec to 5 seconds . Fig - 3A4 , p.301 . BS-EN-60898 & BS-EN-61009-1

Calculating- Earth-fault-loop-impedance . Zs = Uo /Ia .
5 times magnetic-settings - 5 x 6A = 30A : Zs ≤ 230V ÷ 30A = 7.67Ω . re-cap Table 41.3 6A = 7.67Ω .

 

[amberleaf]

Thisone always trips up . Q/As -&-s . 2392 . 2394

Q). When testing a 100mA RCD themaximum-test-current applied via the test-instrument will be ? ( G )
3 x In
5 x In
I x In

 

[amberleaf]

RCDscannot detect . Short-circuits or Overloads . due to their design .

Tosummarise the RCD tests . 30mA -Testing .

IΔn / 2. No-tripin 2 seconds . 30mA ÷ 2 = 15.

 

[amberleaf]

Because it’s Not in the 17[SUP]th[/SUP]- Edition : 2008: or 2011: Doesn’t not mean it did not Exist . “ Pastto Present “ :icon_bs:

Earthing& Bonding - 2[SUP]nd[/SUP] Edition
Incorporatingthe requirements of BS-7671:2001:
IncludingAmendment , No - 2 .

Looped-main-equipotential-bonding . 2006.

Main-equipotential-bonding-conductor(s) should , ideally, Not be looped from service to service . ( METto Water - Gas )

Solution:
Wherea common-bonding-conductor-loops In and Out,to connect to an ,extraneous-conductive-part . The protective-conductor should beleft-unbroken at the connection .

Thisis so that the ( Continuity ) to other-items connected to thebonding-conductor will not be detached , for example . as a result of work beingcarried out to pipework , refer , Regulation - 528-02-04.

Wherea wiring-system is to be installed in proximity to a non-electrical-service, it shall be so arranged that anyforeseeable-operation carried out on either-service will not cause-damage tothe other .

528.3.3. : 17[SUP]th[/SUP] - Edition .
Wherean electrical-service is to be installed in proximity to a non-electrical-services , it shall be so arranged that anyforeseeable-operation carried out on either-service will not cause-damage tothe electrical-service or the converse . Etc .

Apermanent-label bearing the Words “ Safety Electrical Connection - Do Not Remove “ isrequired in a visible-position at or near the point of connection ofevery-main-bonding-conductor to an , Extraneous-conductive-part , and at themain-earthing-terminal where this isseparate from the main-switchgear - Regulation - 514-13-01.

514-13: 2002 / 2004 : Warning-notices: earthing and bonding-connections .
514-13-01 . A permanent-label to BS-951 , with the words “ SafetyElectrical Connection - Do Not Remove “ shall be permanently-fixed in avisible-position at or near : Etc .

514-13: Warning-notices :earthing and bonding-connections .
514-13.1: A durable-label to BS-951 , with the words “ SafetyElectrical Connection - Do Not Remove “ shallbe permanently-fixed in a visible-position at or near : Etc .

Regulation- 528-02-04 :
Wherea wiring-system is to be installed in proximity to a , non-electrical-serviceit shall be so arranged that any , foreseeable-operation carried out on eitherservice will not cause-damage to the other.

 

[amberleaf]

Useful-Junk: 2001 / 2004 .

Means of earthing in Older-Installation(s)

Older-Installation(s)are sometimes found to employ the water-service-pipe as the sole means ofearthing .
Older-Installation(s)may use a Gas , Water orother-metal-service-pipe as a means of earthing . This is Not-permitted .

Ithas never been permitted to use a , Gas-pipe as a means of earthing and , since 1966 , it has not beenpermitted to use any other-service-pipe either .

Necessary-equipotential-bonding-connections, MUST , be made to the Gas-installation-pipe , Water and other metal-service-pipe(s)

542-02-04 : p113
The metalwork of a Gas , Water or other-serviceshall , NOT be used as aprotective-earth-electrode , this requirement does not preclude the bondingof such metalwork as required byRegulation - 413-02 .

 

[amberleaf]

Labelling of the Earthing-Conductor :

it make life easer for any Inspectors inthe near-future .

the earthing-conductor , the conductor connectingthe installation to the ( Means ) of earthing , Mustbe easily-identifiable .
earthing-conductor(s) are not always labelled where requiredmaking it easily possible to mistakenly-disconnect the wrong-conductor.

a Equipotential-bonding-conductor , mayunintentionally be disconnected when intending to disconnect theearthing-conductor .

Earthing-conductor: [ Protective-conductor ]
Water-service-pipe: [ Main-protective-bonding-conductor ]
Gas-installation-pipe: [ Main-protective-bonding-conductor ]
Distribution-board 1 :
Distribution-board 2 :

MET- Safety-electrical-connection Do NotRemove .

 

[amberleaf]

Blast from the Past :

Earthing-Clamps , Not to be used on Cables , Where did it come from . What Edition ??

BS-7671:2001 .

Earthing-Clamps , Not to be used on Cables .
Earthing-Clamps, must not to be used on Paper-insulated / Lead-sheathed orSteel-wire-armoured ( SWA ) cables .

Under, No-circumstance should an earthing-clamp ( Complying with BS-951 or any other type ) be attached to the , Lead-sheath of any cable.
Inthe case of a supply-cable this practice is wrong for , Two-reasons

Thesupply-cable is the property of the , DNO .
Thesecuring of the clamp to the Lead-sheath is likely to damage theconductor-insulation of the supply-cable . and with the cold-flow of the lead ,the connection is liable to loosen over-time . BS-951 :

1999 States in Note-3 . ( second-sentence) to it’sscope that “ such-clamps are not intended for connection to the armour or sheath of a cable “ :icon_bs:

Inthe worst-cases , this practice may lead to increased-risk from the hazards of fire or electrical-shock .

 

[amberleaf]

2001 / 2011:

Blast from the Past : :icon_bs:

Earthing-Clamps , Not to be used on Cables :

Many installations are supplied by , Lead-sheathed-incoming-service-cables, and earthing-facilities are often provided , by DNO by means of a ( Wiped-soldered-joint on to the Lead-sheath ) with an attached-earth-tail to an earthing-block .

Wherean adequate earthing-facility has not been provided , electrical-contractorsare advised always to enquire of the cable-owner ( such as the DNO whether or not such a facility can be made available, it must never be assumed that , because a supply-cable has a , Lead or other metallic-sheathor armour , it is capable of providing an effective-connection to Earth . orthat it is adequate for carrying the ( PFC)

The compressive-forces-exerted by tighteninga clamp , onto most types of armoured ormetal-sheathed-cables ( sufficient toprovide a Low-résistance joint for fault or other-currents to flow ) are liable to cause damage to theconductor-insulation and bedding . such misuse of a clamp is a departure fromthe Regulation - 512-05-01 .

One solution open to the . installation-designer is to make the ,installation part of a , TT - system .

Regulation- 512-05-01
Every item of equipment shall be selected anderected so that it will neither cause harmful-effects to other equipment nor-impair the supply during-normal-service including-switching-operations .

Regulation- 512.1.5. p/114
Every item of equipment shall be selected anderected so that it will neither cause harmful-effects to other equipment nor-impair the supply during-normal-service including-switching-operations .

 

[amberleaf]

Re-cap .

Exposed-conductive-parts : :icon_bs:
Arenot simply conductive-parts that are ,Exposed or Accessible . such as metal-table . the definition of an Exposed-conductive-part is a conductive-part ofequipment which can betouched

Whichis not live-part but which may become live under fault-conditions .

Bydefinition : p/27 . will indicate thatequipment - Means
Electrical-equipment, and electrical-equipment is an item which generates , converts , transmits , distributes orutilises electrical-energy . Etc
So what is an , Exposed-conductive-part:

Be part of electrical-equipment .
Be able to be Touched
Whichis Not normally-live
Butwhich can become live underfault-conditions

Extraneous-conductive-parts :
Extraneous-conductive-part for it is simply any piece of Extraneous-conductive-material , an Extraneous-conductive-part is a conductive-part of the electrical-installation .

Theessence of an , Extraneous-conductive-part is that it is likely to ( Introduce ) earth-potential into a Building / Installation .
Extraneous-conductive-parts : be ( Exposed) Conductive and in generalcontact with the mass of Earth .

p/28. Extraneous-conductive-part.
a conductive-part ( Introduce ) a potential generally Earth-potential .
Not forming-part ofthe electrical-installation .

By definition : p/27

Electrical-equipment :
(abbr : Equipment ) Any item for such purposes as

Generation.
Conversion.
Transmission.
Distributionor utilisation of electrical-energy suchas

Machines’
Transformers
Apparatus
Measuring-instruments
Protective-devices
Wiring-systems
Accessories
Appliances and luminaires .

Electrical-installation :
(abbr : Installation ) An assembly of associated-electrical-equipment having co-ordinated characteristics to fulfil specific-purposes .

 

[amberleaf]

Whilstmeasuring the earth electrode resistance , the earth lead of an earth loopimpedance tester should be connected to ?
- The incoming-line .
- The main-earthing-terminal
- the neutral-conductor only
- The disconnected-earthing-conductor .

Wherea 100mA RCD is protecting a TT installation , when tested at ( ½ ) it should
- Operate within 200mS
- Not operate
- Operate within 300mS
- Operate within 40mS

The ( R[SUP]1[/SUP]+ R[SUP]2[/SUP] ) reading taken at sockets during a continuityof ring-final-conductors test should be approximately ?
r[SUP]1[/SUP]+ r/n / 4
r[SUP]1[/SUP] + r[SUP]2[/SUP] / 4
r[SUP]1[/SUP] + r[SUP]2[/SUP] / 2
R[SUP]1[/SUP] + R[SUP]2 [/SUP]/ 4

Whichof the following test instrument would be most likely to give a reading of 2.5kA ?
Low-résistance-ohmmeter
RCD-tester
Insulation-résistance-tester
Prospective-fault-current-tester.

Theaccuracy of digital test instrument as recommended by Guidance-Note 3 is ?
0.04
0.05
0.02
0.1

Ifthe C.S.A. of a protective-conductor increases , thiswill lead to ?
- A decrease in résistance .
- An increase in résistance .
- An increased ( Zs ) reading
- An reduction in operating-current .

Accordingto GS-38 , test-leads should be . ?
Individually-coloured
Colouredbrown and blue .
Non-flexible
Insulatedto 230V

ATT - installation is protected by a 300mA - RCD . the maximum value ofearth-electrode-résistance is given byGN-3 as . ?
500Ω
1660Ω
100Ω
160Ω

Accordingto GN-3 is the correct-sequence of the following-dead-tests . 1 - Continuity ofthe ring-final-conductors . 2 - Polarity . 3 - Insulation-résistance . 4Continuity of CPC .
2. 3 . 4 . 1 .
4. 1 . 2 . 3 .
1. 2 . 3 . 4 .
4 . 1 . 3 . 2.

When testing a ring-final-circuit , the résistancereadings of ( R[SUP]1[/SUP] + R[SUP]2[/SUP]) will be . ?
Approximately 1.87 x R[SUP]1[/SUP]+ Rn
Approximately 2 x R[SUP]1 [/SUP]readings
Approximately 1.67 x R[SUP]1[/SUP] & Rn readings .
Approximately 1.67 x R[SUP]1[/SUP] & R[SUP]2 [/SUP]readings .

Whichof the following should be carried out when conducting aninsulation-résistance-test . on a 2 -way lighting-circuit . ?

Ensurethat Edison-screw light bulbs are connected in the Line-conductor only .
Bridgeout the switches .
Ensurethat both switches are in the on-position .
Operate all switches duringthe test .

It is often necessary to control a lampfrom more than one location , By utilising 2-way switches and strappers ( thecables in between the two operating switches )
Wecan effectively control the lamp from 2-different locations , such asthe top and bottom of stairs , known asthe “ conventionalmethod “

Whichcolumn would you record the results from the long-lead-test-method used todetermine continuity of the protective-conductors . ? Wander-lead-method .
Zs.
PFC.
R[SUP]2[/SUP].
(R[SUP]1[/SUP] + R[SUP]2[/SUP])

Which of the following tests would be carried out first ?
Earth-fault-loop-impedance
Insulation-résistance
Continuity of ring-final-conductors
Prospective-fault-current

 

[amberleaf]

The minimum-test-voltage that should be appliedwhen testing the insulation-résistance of a SELVcircuit is ?
500V d.c.
500V a.c.
250V d.c.
250V a.c.

An RCD when tested at 100% ( x1 times ) of its trip-rating should ?
Not-trip
Trip within 300mS
Trip within 40mS
Trip within 100mS

Some of the essential andoptional-information required on the , Electrical-Installation-certificate and Minor-Electrical-Installation-Work-certificate is ?
Number of rooms , type of lighting ,outdoor-supplies
Floor-area, separate building , number of floors
Means of earthing, main-protective-conductors andsupply-characteristics
Name of sub-contractor , invoice , contact-number

Before carrying out an Insulation-résistance test ?
Carry out verification of voltage-drop. ► ( Regulations - 612.14. p/194 . Note : Verification of voltage-drop is not normallyrequired during initial-verification )
Ensure supply is switched on
Contact local-authority-building-control
Safely-isolate and consider electronic-equipment andvoltage-sensitive-equipment

Prospective-fault-current-measurement ensures that ?
Cables can carry the required-load-current
The consumer-unit-main-switch can be operated during a fault
The overcurrent-protective-devices at that point in the installation can disconnect ( Overload / Overloaded - Overcurrent )
The main-fuse will operate in the event of afault .

Overcurrent-Protective-Devices :
Protection against overload , & short-circuits in electrical-equipment .
O.S.G.- p/23 Note . RCBOs - Overload , Short-circuit , Earth-fault . MCB/ RCBO ( Overload-protection - Fuses ) its inthe Questions

A Minor-electrical-certificate does not require details of ?
System-earthing-arrangements
Departures from BS-7671:
Method of fault-protection
Prospective-fault-current. ( PFC )

Once an Electrical-Installation-certificate has been completed theoriginal should be ?
Sent to the local-building-control
Retained by the electrical-contractor
Given to the person ordering the work
Given to the tenant of the building .

Test-Leads to GS-38 should have ?
1mm exposed-probe , non-fused and finger-barriers
2mm exposed-probe , non-fused-lead or current-limiting and finger-barriers
2mm exposed-probe , fused-lead or current-limiting and finger-barriers
1mm exposed-probe , fused- lead or current-limiting and finger-barriers

► 2mm exposed-probe ( for live-testing ) “ Fingers “ or Hands
► 4mm exposed-probe ( for dead-testing )

During the initial-inspection and testing sight would indicate a fault such as ?
Overheating
Equipment-overheating
Vibration of transformer-cover
Damaged-equipment .

 

[amberleaf]

Metallic supply-pipework can be used for anearth-electrode if ?
It is water-utility-pipework
It is other than water-utility-pipework
It is an unused-gas-pipe that is less than10-years old
It is other than utility-pipework providing-precautions have been taken . BS-7671:2011 . p/159 - 542.2.6.

If running in permitted-zones are used as protection against impact , whatextra-measure would be required if the installation was in a domestic-premises ?
Run cables with capping-fitted
All circuits protected with a30mA RCBO
Cables to have additional-protection by means of 30mA RCD BS-7671:2011/125 . 522.6.102
Cables to have additional-protection by means of 100mA RCD

When assessing-circuits for any need of continuity of service , the following-characteristic that does notneed to be considered is ?
Multiple-power-supplies
Selection of earthing-system
Lighting-protection ( BS-7671:2011. p/ 49 . 361.1
Number of circuits

When automatic-disconnection of supply is used as a measure of protection , additional-protectionby RCD shall be provided for ?
Mobile-equipment having a rating of greater than 32A
Socket-outlets in commercial and industrial-locations
Only for sockets-rated at 32A or less where it is reasonable to expect they may be used to supply-equipment for use outdoors
Socket-outlets-rated at 20A or less in a domestic-installation ( BS-7671:2011: p/54. 411.3 )

All circuits in a location containing a bath or shower shall have ?
A disconnection time of 0.4s
Be installed at a depth of at least 50mm
Be installed using earthed-conduit
Additional-protection by a 30mA RCD . ( BS-7671:2011: p/199 . 701.411.3.3.

The installation reference for multicore-cables clipped-direct is ?
30
C ( BS-7671:2011. p/318 . number - 20
A
13

Automatic-disconnection of supply is used as a method of protectionfor ?
Indirect-contact
Basic-protection
Fault-protection ( BS-7671:2011: definitions )
Direct-contact

 

[amberleaf]

How things change - 1991 / 2011 : 15[SUP]th[/SUP]/ 16[SUP]th[/SUP] - 17[SUP]th[/SUP] edition 2011:

Sixteen Edition 1991:

ThisEdition was issued on 10 may 1991 . it isintended to supersede the fifteen-edition , fifteen-edition will bechanged to the sixteen-edition to take effect from 31-december 1992.

130-09: Additions and Alterationsto an Installation : 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
130-09-01. No addition or alteration , temporaryor permanent , shall be made to an existing-installation , unless it has been ascertainedthat the rating and the condition of any existing-equipment , including that ofthe supplier , which will have to carry any additional-load is adequate for the altered-circumstances andthe earthing-arrangement is also adequate .

132.16 : Additions and Alterationsto an Installation : 17[SUP]th[/SUP] - edition
Noaddition or alteration , temporary or permanent , shall be made to anexisting-installation , unless it has been ascertained that the rating and thecondition of any existing-equipment , including that of the distributor , will be adequate for thealtered-circumstances , furthermore , the earthing and bonding-arrangements ,if necessary for the protective-measure applied for the safety of the additions and alteration , shall be adequate .

Comparing things form the past - Editions “ What’s in a Wording “

 

[amberleaf]

Comparing things from the past - Editions

15[SUP]th[/SUP]/ 16[SUP]th[/SUP] . 1991 / 1992 .
Earthed-equipotential-zone:
A zone within which , exposed-conductive-partsand , extraneous-conductive-parts are maintained at substantially the sane-potential by-bonding , such that , underfault-conditions , the differences in potential between-simultaneously-accessible , exposed and extraneous-conductive-parts will not cause electric-shock .

Earthing: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
The act of connecting the , exposed-conductive-partsof an installation to themain-earthing-terminal of an installation .

Earthing: 2011 :
Connection of the exposed-conductive-parts of an installation to the main-earthing-terminalof that installation .

Equipotential-bonding: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
Electrical-connection-maintaining various , exposed-conductive-parts and extraneous-conductive-parts atsubstantially the same-potential .

Equipotential-bonding: 2011:
Electrical-connection-maintaining various , exposed-conductive-parts and extraneous-conductive-parts atsubstantially the same-potential . ( see also Protective-equipotential-bonding )

Exposed-conductive-part: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
A conductive-part of equipment which can be touched and whichis not a live-part but which may become live under fault-conditions .

Exposed-conductive-part: 2011:
Conductive-part of equipment which can be touched and whichis not a normally live , but which can become live under fault-conditions .

Extraneous-conductive-part: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
A conductive-part liable to introduce a potential , generallyearth-potential , and not forming-part of the electrical-installation .

Extraneous-conductive-part: 2011:
A conductive-part liable to introduce a potential , generally Earth-potential, and not forming-part of the electrical-installation .

Prospective-fault-current: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
The value of overcurrent at a given-point ina circuit resulting from a fault of negligible-impedance betweenlive-conductors having a difference ofpotential undernormal-operating-conditions , or between a live-conductor and an , exposed-conductive-part.

Prospective-fault-current: 2011: ( Ipf )
The valueof overcurrent at a given-point in a circuit resulting from a fault ofnegligible-impedance between live-conductors having a difference of potential under normal-operating-conditions , or between a live-conductor and an ,exposed-conductive-part .

Earth-fault-current: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
A fault-currentwhich flows to Earth .

Earth-fault-current: 2011:
A current resulting from a fault of negligible-impedancebetween a line-conductor and an , exposed-conductive-part or a protective-conductor .

Earth-fault-loop-impedance: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
The impedance of theearth-fault-current-loop starting andending at the point of earth-fault , this impedance is denoted by the symbol; ( Zs )

Earth-fault-loop-impedance: 2011:
The impedance of theearth-fault-current-loop starting andending at the point of earth-fault , this impedance is denoted by the symbol; ( Zs )

Gas-installation-pipe: 15[SUP]th[/SUP] / 16[SUP]th[/SUP]
Any-pipe, not being a service-pipe ( other thanany-part of a service-pipe comprised in a primary-meter-installation ) or apipe comprised in a gas-appliance , for conveying gas for a particularconsumer and including any associated-valve or other-gas-fitting.

Gas-installation-pipe: 2011:
Any-pipe, not being a service-pipe ( other thanany-part of a service-pipe comprised in a primary-meter-installation ) or apipe comprised in a gas-appliance , for conveying gas for a particularconsumer and including any associated-valve or other-gas-fitting.

Has thing changed much .