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

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Other Considerations

There are Additional Regulations and Codes of Practice that Need to be considered during the design of an
be considered during the design of an installation. These will affect the choice of consumer unit.
Division of Installation : Section 314.1 Calls for the Installation to be so Divided to:
( a ) Avoid Hazards and Minimize Inconvenience in the Event of a Fault
( b ) Reduce the Possibility of Unwanted Tripping of the RCD due to Excessive Protective Conductor Currents.

To Comply with these Requirements the Circuits of an Installation should Not be Connected to a Single RCD, as this could Lead to Loss of Supply to the Entire Installation in the Event of a Fault on One Circuit,
clearly Inconvenient for the User of the Building

All Circuits of an Installation should Not be Connected to a Single RCD :

● BS 5839-6:2004 Fire detection and Fire alarm systems for buildings
This Code of Practice has particular requirements for dwellings. This document makes reference to the power supply to such systems
and mentions RCD’s. The circuit supplying these systems should preferably not be protected by an RCD. This however is going to be
difficult to achieve if the circuit supplying these systems is buried in the walls and standard domestic wiring systems are used. Indeed the supply cables would need to be specially protected in earthed metal conduit etc. for RCD protection not to be used.

According to BS 5839, circuits supplying fire or smoke alarms in dwellings can be protected by an RCD provided that either:
(i) The RCD serves only that circuit. For example with the use of an RCBO ,
(ii) The RCD should operate independently of any RCD feeding socket outlets or portable equipment ,

Where RCD Protection is Needed for Smoke Detector Circuits it should Preferably be Supplying that Circuit ,

● The following options, each with their own benefits, can be considered by the installation designer. ( Electrician )

Consumer Unit Arrangements “ Not Permitted “
A consumer unit with a 30mA RCD main switch would not meet the requirements of the regulations for 3 main reasons:
Consumer Unit Arrangements “ Not Permitted “
A consumer unit with a 30mA RCD main switch would not meet the requirements of the regulations for 3 main reasons:
• The Fire detection circuit and the socket outlet circuits share a common RCD. This would be against the requirements of BS 5839.
• The cumulative effects of electronic equipment in the modern home, is such that some current is likely to flow in the protective conductor.
A 30mA RCD will trip between 15-30mA. This could cause unwanted tripping, regulation 314.1 (iv) refers.
• Any fault would result in the loss of all the lighting, this could in itself cause a hazard and the lack of power to the fridge / freezer
circuit for example would be very inconvenient. Regulation 314.1 (i)

A Consumer Unit with a 30mA RCD Main Switch would Not meet the Requirements of the Regulations

● Consumer Unit Arrangements Option 1
Main Switch with RCBO’s On All Circuits

A standard main switch disconnector controlled consumer unit could
be used with every circuit having individual RCD protection at 30mA.
This could be achieved by selecting RCBO’s for every outgoing
circuit instead of the usual MCB’s. A fault on any circuit would not
affect other circuits and hence all relevant regulations would be met by such a design.

Selecting RCBO’s for every outgoing circuit meets all relevant regulations

● Consumer Unit Arrangements Option 2
Split Load Twin RCCB plus Dedicated RCBO
This arrangement provides a dedicated 30mA RCBO for the smoke
detector circuit, but combines the rest of the circuits across two
further 30mA RCCB’s. Careful arrangements of the circuits can
reduce the likelihood of nuisance tripping, thereby limiting the
inconvenience or potential hazards that a loss of supply can cause by limiting the number of circuits affected.

This arrangement provides a dedicated RCBO for the smoke detector circuit

● Consumer Unit Arrangements Option 3

Split Load 3 RCCB Board
This arrangement provides a 30mA RCCB for the smoke detector
circuit which could also supply other circuits e.g. lighting, and
combines the rest of the circuits across two further 30mA
RCCB’s. Careful arrangements of the circuits can reduce the
likelihood of nuisance tripping, thereby limiting the inconvenience
or potential hazards that a loss of supply can cause by reducing the number of circuits affected.

This arrangement provides a RCD for the smoke detector circuit which could also supply other circuits e.g. lighting

● Consumer Unit Arrangements Option 4
Split Load Twin RCCB
This arrangement provides two separate 30mA RCCBs with the
circuits spread across both. The design of the circuit arrangements
must ensure the smoke detector is not fed from the same RCD as
socket outlets. Careful arrangement of the other circuits can reduce
the likelihood of nuisance tripping, thereby limiting the inconvenience
or potential hazards that a loss of supply can cause. However with
all circuits now over just two devices certain compromise must be accepted

The smoke detector must not be fed from the same RCD as socket outlets

● Consumer Unit Arrangements Option 5

Split Load Twin RCCB plus unprotected circuit
Under the 17th Edition requirements it is still possible to install some
circuits in domestic premises that are not fed via an RCD. Different
wiring systems would need to be used. The cost of installation could
rise considerably if most circuits were installed using armoured cable or earthed metal conduits.

The smoke alarm circuit could be installed in such a way to negate
the need for RCD protection, this may be possible by using one
of the other wiring methods described in 522.6.6 for the length of
run that the cable is in the wall (use of earthed metal conduit for
example). Or depending on the layout of the property there maybe an
attached garage for example where surface wiring might be possible.
The requirements of that regulation are therefore not applicable.

The smoke detector must not be fed from the same RCD as socket outlets

The level of compliance with the Regulations would therefore be the
same as option 2 Split Load Twin RCCB plus Dedicated RCBO.

If the smoke alarm circuit is not to be protected by an RCD it must be installed using

a method from (i) to (iv) of regulation 522.6.6

239- : Guidance for Recipients on the Recommendation Codes

Only One Recommendation Code should have been Given for Each Recorded Observation ,
Recommendation Code (1)
Where an Observation has been Given a Recommendation Code (1) ( Requires Urgent Attention )
The Safety of those Using the Installation may be at Risk ,
The Person Responsible for the Maintenance of the Installation is Advised to take Action without Delay to Remedy the Observed Deficiency
In the Installation , or Take Other Appropriate Action ( Such as Switching Off and Isolating the Affected Part(s) of the Installation )
To Remove the Potential Danger ,
The N----- Approved Contractor Issuing this Report will be Able to Provide Further Advice :

It is Important to Note that the Recommendation Given at Section 1 Next Inspection of this Report for the Maximum Interval until
The Next Inspection , is Conditional Upon all Items which have been Given a Recommendation Code 1 being Remedied without Delay ,

Recommendation Code (2)
Recommendation Code 2 ( Requires Improvement ) indicates that , Whilst the Safety of those Using the Installation may Not be at Immediate Risk ; Remedial Action should be Taken as Soon as Possible to Improve the Safety of the Installation to the Level Provided by the National Standard for the Safety of Electrical Installations BS - 7671

The N----- Approved Contractor Issuing this Report will be Able to Provide Further Advice :
Items which have been Attributed Recommendation Code 2 should be Remedied as Soon as Possible

Recommendation Code (3)
Where an Observation has been Given a Recommendation Code 3 ( Requires Further Investigation ) the Inspection has Revealed an Apparent Deficiency which could Not , Due to the Extent or Limitations of this Inspection , be Fully Identified , Items which have been Attributed Recommendation Code 3 should be Investigated as soon as Possible
The Person Responsible for the Maintenance of the Installation is Advised to Arrange for the N----- Approved Contractor Issuing
This Report ( or Other Competent Person ) to Undertake Further Examination of the Installation to Determine the Nature and Extent of the Apparent Deficiency

Recommendation Code (4)
Recommendation Code 4 ( Does Not Comply with BS-7671 ( as Amended ) will have been Given to Observed Non-Compliance(s)
With the Current Safety Standard which Do Not Warrant One of the Other Recommendation Codes ,
It is Not Intended to Imply that the Electrical Installation is Unsafe , but Careful Consideration should be Given to the Benefits of Improving these Aspects of the Installation ,
The N----- Approved Contractor Issuing this Report will be Able to Provide Further Advice ,

 

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Frequency of Inspections
The frequency of the periodic inspection and testing must be determined taking into account:
1. the type of installation
2. its use and operation
3. the frequency and quality of maintenance
4. the external influences to which it is subjected.
It is recommended that periodic inspection and testing is carried out at least every:
1. 10 years for a domestic installation
2. 5 years for a commercial installation
3. 1 year for swimming pools
Other instances when a periodic inspection should be carried out are:
1. When a property is being prepared to be let
2. Prior to selling a property or when buying a previously occupied property
Scope
The requirement of BS-7671 IEE Wiring Regulations, for periodic Inspection and Testing is for INSPECTION comprising careful scrutiny of the installation without dismantling, or with partial dismantling as required, together with a sequence of tests considered appropriate by the person carrying out the inspection and testing.

Electrical Testing - Legal Requirements 239-

Letting
You must maintain the electrical installation and any equipment provided by you, in a safe condition.
The Landlord and Tenant Act 1985 requires landlords to ensure the electrical installation is safe when the tenancy begins, and that it is maintained in a safe condition throughout that tenancy.
One way of ensuring safety is to undertake a regular visual inspection of the installation, looking for any obvious signs of damage such as damaged cables, socket-outlets showing scorch marks, etc.
In addition, the Institution of Electrical Engineers recommends that electrical installations are formally inspected and tested by a competent person on change of occupancy, and at least once every ten years.
Businesses
Any business premises from Guest houses, Shops, Offices or Hotels, are required under the Electricity at Work Regulations, that the electrical installation be checked. to satisfy this requirement.
Building Regulations
Part P of the Building Regulations (England and Wales) was introduced by the Government on January 1st 2005. It is designed to reduce accidents caused by faulty electrical installations and to prevent incompetent installers from leaving electrical installations in an unsafe condition.
Part P applies to the following situations:
• Dwelling houses and flats
• Dwellings and business premises that have a common supply eg shops that have a flat above
• Common access areas in blocks of flats such as corridors or staircases
• Shared amenities in blocks of flats such as laundries or gyms
• In or on land associated with dwellings – such as fixed lighting or pond pumps in gardens
• Outbuildings such as sheds, detached garages and greenhouses
Approved Document P is called ‘Electrical Safety’ and will be complied with if the standard of electrical work meets the ‘Fundamental Requirements of Chapter 13 of BS7671'.
Section P1 of Part P states: ‘Reasonable provision shall be made in the design, installation, inspection and testing of electrical installations in order to protect persons from fire and injury’
Section P2 of Part P states: ‘Sufficient information shall be provided so that persons wishing to operate, maintain or alter an electrical installation can do so with reasonable safety’
Part P applies only to fixed electrical installations that are intended to operate at low voltage or extra-low voltage which are not controlled by the Electricity Supply Regulations 1988 as amended, or the Electricity at Work Regulations 1989 as amended.
Note 1: The Workplace (Health, Safety & Welfare) Regulations (1992) apply in common parts of flats and similar buildings if people such as cleaners and caretakers are employed to work in them.
Note 2: The Electricity at Work Regulations (1989) cover all electrical work carried out professionally and the competence of the individuals carrying out that work
Note 3: Part P is concerned with safety and does not directly cover system functionality
Note 4: Part P does not specifically cover dwellings in places of work normally covered by the Electricity at Work Regulations (1989), such as caretakers flats in schools, MOD barracks etc.

The Periodic Inspection Report form is intended for reporting on the condition of an existing electrical installation.
You should have received an original Report and the contractor should have retained a duplicate. If you were the person ordering this Report, but not the owner of the installation, you should pass this Report, or a full copy of it, immediately to the owner.
The original Report is to be retained in a safe place and be shown to any person inspecting or undertaking work on the electrical installation in the future. If you later vacate the property, this Report will provide the new owner with details of the condition of the electrical installation at the time the Report.
The 'Extent and Limitations' box should fully identify the extent of the installation covered by this Report and any limitations on the inspection and tests. The contractor should have agreed these aspects with you and any other interested parties (Licensing Authority, Insurance Company, Building Society etc) before the inspection was carried out.
The Report will usually contain a list of recommended actions necessary to bring the installation up to the current standard. For items classified as 'required urgent attention', the safety of those using the installation may be at risk, and it is recommended that a competent person undertakes the necessary remedial work without delay.
For safety reasons, the electrical installation will need to be re-inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated in the Report under 'Next Inspection.'
Accessories and Switchgear
It is recommended that a random sample of a minimum of 10 per cent of all switching devices is given a thorough internal visual inspection of accessible parts to assess their electrical and mechanical condition.
Protection against Thermal Effects
The presence of fire barriers, seals and means of protection against thermal effects will be verified.
Protective Devices
The presence, accessibility, marking and condition of devices for electrical protection, isolation and switching will be verified. It should be established that each circuit is adequately protected with the correct type, size and rating of fuse or circuit-breaker. The suitability of each protective and monitoring device and its overload setting will be checked.
Visual Inspections
Joints and Connections
It is not practicable to inspect every joint and termination in an electrical installation, nevertheless a sample inspection is made. An inspection is made of all accessible part of the electrical installation e.g. switchgear, distribution boards, and a sample of luminaire points and socket-outlets to ensure that all terminal connections of the conductors are properly installed and secured. Any signs of overheating and conductors, terminations or equipment will be thoroughly investigated and included in the Report.

239- Regs : page – 340 ( PS this will come up along the Line )
✔’
indicates that an inspection or a” test “ was carried out and that the result was satisfactory
‘✗’
indicates that an inspection or a” test “was carried out and that the result was Not satisfactory( Applicable for a Periodic Inspection Only )

N/A’ indicates that an inspection or a” test “was not applicable to the particular installation

LIM’ indicates that, that exceptionally, a limitation agreed with the person ordering the work prevented the Inspection being Carried Out ( Applicable for a Periodic Inspection Only )

prevented the inspection or test being carried out

 

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239- Test !! It is Big Exam , Good Luck for your examination , Amberleaf
Please have a Look at what am down Loading it will Help you Somewhere along the Line
PS some Old Notes

● Give THREE reasons for carrying out a polarity test on an installation, as required by BS-7671
● The resistance of an earth electrode is to measured. If a mains supply is unavailable, state the
(a) instrument to be used
(b) terms used to describe the TWO other test electrodes.

● State (a) why it may not be possible to obtain a measured value of loop impedance for a circuit protected by an RCD (b) how this value may be determined without the use of a special instrument
● A loop impedance test is to be conducted on a radial socket outlet circuit. State
(a) where in the circuit the test should be made
(b) TWO conditions that may affect the validity of the measured value as a comparison to the maximum value
● State THREE reasons for the use of a 20mA RCD
● In the formula IΔ n = 50/Zs (a) state what is represented by ‘50’ (b) the maximum residual current rating of the RCD required, when the value of Zs is 500Ω
● The PFC at the origin of an installation is to be measured. State the
(a) instrument to be used
(b) measurement units
(c) importance of the breaking capacity of the protective devices at the origin
● Section B – Answer ALL SIX questions Questions 21 to 26 all refer to the following scenario and Fig. 1 (attached).
Fig.1 shows the main intake and circuit arrangements for the new electrical installation in a refurbished dentist’s surgery. The heating, ventilating and air-conditioning unit (HVAC), located outside the building is supplied using p.c.v./p.c.v./s.w.a. multicore cable. All other circuits are wired using p.v.c. single-core cables enclosed in concealed p.v.c. conduit and surface trunking (c.p.c’s are the same size as the phase conductors). The lighting is a mixture of tungsten filament, fluorescent and PIR-controlled exterior security lights. The installation has been completed and is ready for inspection and testing.
● State the
(a) type of inspection and test to be completed (b) certificate that will need to be completed (c) signatures that are required on the certificate in b) (d) status of the signatories (e) documents that must accompany the certificate in b) (f) information regarding the incoming supply that should be recorded on ONE of the documents in e) (g) person who should keep the original completed documents

“ What types of electrical work DOES Part P cover “

Part P applies to electrical installations in buildings or parts of buildings comprising:
> dwelling houses and flats;
> dwellings and business premises that have a common supply – for example shops
and public houses with a flat above;
> common access areas in blocks of flats such as corridors and staircases;
> shared amenities of blocks of flats such as laundries and gymnasiums.

Part P applies also to parts of the above electrical installations:
> in or on land associated with the buildings – for example Part P applies to
fixed lighting and pond pumps in gardens;
> in outbuildings such as sheds, detached garages and greenhouses.

“ How will compliance with Part P be enforced ”

Electrical installations within dwellings are now covered by Part P (and others) of
the building regulations. As such, failure to comply with the building regulations is a
criminal offence and Local Authorities have the power to require the removal or
alteration of work that does not comply with the requirements.

As with other building regulations, they must be followed. This ensures compliance,
as well as regulated enforcement of standards and ultimately quality of workmanship

“ What benefits is Part P aiming to provide “

it is expected that bringing electrical work in dwellings under building regulations
control will reduce the number of deaths, injuries and fires caused by faults in
electrical installations. It is also expected that nationally, Part P will lead to an overall
improvement in the competence of electrical contractors and to an improvement in the quality of electrical work.

Insurance companies are not yet offering cheaper home insurance if your electrical
installation is checked compliant to latest regulations and Part P.

We are seeing 'required' demands from insurance companies that are let through
landlords - safety and Part P compliant against any recent updates / changes.

Longer term (2007 onwards) we expect additional movement through the government
and through insurance companies to begin to 'drive' Part P, requiring electrical
certification to be confirmed against building works since 2005 and creating a
framework for confirmation of safety upon change of ownership (conveyance).

Electrician : 2392-10 ←

As Part P is now a regulatory requirement for electrical installations within homes,
insurance companies will challenge claims when faced with related electrical issues,
with possible failure ( invalidation ) of the claim, if Part P was not followed.

Building Regulations

The Requirements of this Part Apply Only to Electrical Installations That are Intended to Operate at Low or Extra-Low Voltage – are :-
(a) in Dwellings
(b) in the Common parts of the Buildings Serving one or more Dwellings , but Excluding power Supplies to Lifts ,
(c) in a Building that Receives its Electricity from a Source Located within or Shared with a Dwelling , and
(d ) in garden or in or on Land Associated with a Building where the Electricity is from a Source Located within or Shared with a Dwelling

** Extra Low Voltage = 50v ac or 120v ripple free dc
** Low Voltage = not exceed 1000 V ac or 1500 V dc between conductors,
or 600 V ac or 900 V dc between conductors and earth.

Standard domestic 'mains' electricity = Low Voltage (as defined above)

Simply, Part P aims to tighten and enforce electrical regulations as defined by the
Institute of Electrical Engineers (IEE). These regulations now mean *most* electrical
changes, additions and updates within dwellings fall under Part P, and must comply
with the IEE, the BS-7671 wiring regulations

What is Periodic Inspection & Testing
The 'Electricity at Work Regulations 1989' in Regulations 4(1) and 4(2) lay down the requirement to ensure that an electrical installation should be designed, installed, constructed and maintained in a safe manner at all times. The basis for periodic inspection and testing is derived from Guidance Note 3 of the 'IEE Wiring Regulations BS7671:2008'.
Inspection & Testing of an electrical installation generates a Periodic Inspection Report which is a condition report supplemented by testing results. The Periodic Inspection Report will normally consist of:
• Client information and details of the installation
• Supply characteristics and Earthing arrangements
• Observation & Recommendations
• Extent & Limitations of Testing
• Summary of the Inspection
• Inspection & Test Schedules
'IEE Inspection and Testing Guidance Note 3' “ GN-3 “
The Testing of an electrical installation follows BS-7671:2008 and comprises of:
• C.P.C Continuity
• Ring Circuit Continuity
• Insulation Resistance
• Polarity
• Earth Fault Loop Impedance
• Prospective Fault Current
• Operation of Residual Current Devices
• Functional Testing
Testing is carried out as far as is reasonably practicable as defined in EAWR 1989.

 

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The Electricity at Work Regulations

Regulation 3: Persons on Whom Duties are Imposed by these Regulations
Regulation 4: Systems, work activities & protective equipment
Regulation 5: Strength and capability of electrical equipment
Regulation 6: Adverse or hazardous environments
Regulation 7: Insulation, protection and placing of conductors
Regulation 8: Earthing or other suitable precautions
Regulation 9: Integrity of Referenced Conductors
Regulation 10: Connections
Regulation 11: Means for Protecting from Excess of Current
Regulation 12: Means of cutting off the supply and for isolation ( Isolation from sources of energy )
Regulation 13: Precautions for work on equipment made dead
Regulation 14: Work on or near live conductors
Regulation 15: Working space, access and lighting
Regulation 16: Persons to be competent to prevent danger and injury :

The On-site Guide is intended to enable the competent electrician to deal with small installations (up to 100 A, 3-phase )

“ Inspection & Testing before into Service “ 2392-10 Electrical Installations should be Inspected and Tested as Necessary and Appropriate During and the End of Installation , Before they are taken into Service , to Verify that they are Safe to Use ,Maintain and Alter and Comply with Part P of the
Building Regulations and with any Other Relevant Parts of the Building Regulations

An HSE Inspector , whilst visiting a high-volume manufacturing plant , spots a serious problem with a complex machine –whilst it is running through a long “ cycle “ The machine IS under human supervision , which one of the following actions , available to him/her , is most appropriate in this case ,
( Issue a Deferred prohibition notice )

this will allow the machine to complete its “ cycle ( with safeguards’ in place ) after which time , it MUST NOT
Be used until the fault is repaired this option is available to Inspectors in this cases where shutting down in “ mid-cycle “
Can itself – cause danger / expensive damage

“ Apprentice “ Domestic Electrical Installation Condition Report :
A Visual Condition Report , which includes Inspection but Not Testing :

A Periodic Inspection Report ( Including Inspection & Testing )

Residual Current Devices ( RCDs ) are used Extensively in Installation to Provide Fault Protection and / or Additional
Protection Against Electric Shocks ,17th Edition of the IEE Wiring Regulations most if not all , Final Circuits in new or rewired
Installation in Domestic Premises need to be Provided with Additional Protection by an RCD having a Rated
Residual Operating Current ( I∆n ) – 30mA and an Operating Time Not Exceeding 40mS at ( 5 I∆n )

While RCDs Provide an Enhanced Level of Shock Protection , Precautions should be Taken to Avoid Unwanted Tripping of the Devices on Healthy Circuits , ( Repeated Unwanted Tripping is Likely to Damage User Confidence in RCDs , )

Unwanted Tripping of RCDs can be Caused by the Currents that may flow in the Protective Conductors of Circuits Supplying
Certain Items of Class 1 ( Earthed ) Equipment During their Normal Operation , Such Items Include Equipment Incorporating :

● Electrical Noise ( Radio Frequency )
Suppression Filters , such as Personal Computers , Hi-fi Equipment , TVs , DVDs
● Heating Elements , such as Cookers , Water Heaters or Radiant Heaters ,
● Motors , such as Fridges & Freezers ,

To avoid Unwanted Tripping , RCDs Should be so Selected and Circuits so Subdivided , that any Protective Conductors Current
Expected to Occur During Normal Operation of the ( Load(s) will be Unlikely to Cause Tripping of the Device ,
It is worth Noting that Product Standards Permit Certain Equipment such as Personal Computers , to Create up to ( 3 mA )
Of Leakage Current in the Protective Conductor ,
Tripping of RCDs the Number of Items of Protective Conductor Current-Generating Equipment per Circuit ,
And the Number of Circuits Served by each RCD , needs to be Sufficiently Small ,

As a Rule of Thumb , Tripping of an RCD may Result if the Total Protective Conductor Current in the Circuit(s)
It Serves Exceeds 50% of its Rated Residual Operating Current that is 15 mA for a 30 mA Device ,

“ Routine Inspection & Maintenance of Fire Safety Installations “

Once Fire Safety Installations , such as Fire Detection and Fire Alarms Systems and Emergency and Escape Lighting Systems ,
Are in Use , they should be Subject to Regular Checks and Maintenance , these Checks are Split into Daily , Weekly , Monthly ,
Three-Monthly , Six-Monthly , and Yearly Checks :
● the Indication of Normal Operation of the Control Panel of a Fire Detection and Alarm Systems or Emergency and Escape Lighting Systems ,

● Weekly Checks includes , Amongst other things , Standby Batteries are in good Condition and the Control Equipment is Able to Receive a Fire Signal and Initiate the Evacuation Procedure :

● Amongst other things , the Operation of Standby Generator Sets should be Checked Monthly , involving the Simulation of Power Failure and Allowing the Systems to be Energised for One Hour , Additionally , the Failure of the Supply to the Normal Lighting should be Simulated Monthly , and all Signs and Luminaires Inspected to Determine that they are Functioning Correctly ,

● Annual Checks by Competent Person(s)
Should be made amongst other things ,of the Fire Detection and Alarm Systems , Self-Contained Luminaires over Three-Years old and Sprinkler Systems ,

 

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City & Guilds Unit Breakdown

Unit 201
This unit is the first to complete and comprises of the following sections:
● Identify the legal requirements
● Identify occupational specialism’s
● Identify sources of technical information
This is a general Health and Safety unit that also covers some of the fundamentals of the industry, such as the use of drawings.
Unit 202
The second unit and the first one that involves the student thinking more and using their Math’s and Physics skills.
● Describe the application of basic units used in electro technology
● Describe basic scientific concepts related to electro technology
● Describe basic electrical circuitry and applications
● Identify tools, plant, equipment and materials
This unit introduces standard units as well as the theory and calculation behind resistance and resistivity and other technical concepts. Ohms Law is introduced at this point.
Unit 203
The third unit is an amalgamation of the first two. It splits Health and Safety and Electrical Principles into two but also requires both parts to be passed independently to achieve the certificate.
● Safe systems of working
● Using technical information
● Electrical machines and a.c. theory
● Polyphase systems
● Over current, short circuit and earth fault protection
Some of the more useful fundamentals of electrical installation are covered, such as protective devices and the purpose of earthing. Motors and a.c. theory also come into play.
This unit also contains Unit 204 which is a practical assessment involving the measurement of 3 phase supplies, both voltage and current and on and off load and the measurement of the different voltages and currents found in a standard fluorescent circuit. This is assessed internally but is needed to claim for your final certificate.
Unit 205
The unit that concludes the level 2 focuses on installation design and Regulations and covers the following subjects.
● Regulations and related information
● Purpose of specifications and data
● Types of installations
● Undertaking electrical installation
As part of unit 205 you have to complete Unit 206, you are expected to complete a large practical task (which can vary centre to centre) that consists of different wiring system such as steel conduit, trunking, swa and lighting and socket outlet circuits.
Unit 301
The start of the level 3 takes all the aspects of level 2 and increases the depth of content. It works in the same way as Unit 203 in that it is split into 2 parts, Health and Safety and Science and Principles and you must achieve a pass in both sections. Expect to cover the following:
● Comply with Statutory Regulations and organisationaI requirements
● Apply safe working practices and follow accident and emergency procedures
● Work effectively and develop competences
and for the second part
● Understand the functions of electrical components
● Understand electrical supply systems, protection and earthing
Unit 302
This unit concentrates on Inspection, Testing and Commissioning and takes the theory up to level 3 where you are expected to test live installations. It is made up of a practical assessment and a 2 hour written examination covering all aspects of Inspection and Testing.
Unit 303
Almost identical to unit 302, this unit concentrates on Fault Diagnosis and Rectification and finishes in a practical assessment and a 2 hour written exam.
Electrical Qualifications 2007

The actual AM2 is split into 4 sections:
• Section A involves a composite installation. It is a partially completed installation which you must finish. You need to know how to terminate SWA (armoured) cable, MIMS (Mineral Insulated Metal Sheathed or simply Pyro to many) and be comfortable with simple motor circuits, although you are given a wiring diagram. Once complete a visual and a functional test needs to be carried out.
• Section B involves an inspection and test of the installation
• Section C involves safe isolation procedures and a risk assessment
• Section D is fault diagnosis and rectification
AM2 Hints and Tips
Below are some ideas to help you pass the AM2 practical exam.
• Practice reading from a circuit diagram before you start
• Be especially comfortable with motor circuits and following the wiring diagram given to you beforehand
Be comfortable with lighting circuits in singles, make sure you know how to wire a landlords override switch and a Two-Way and Intermediate Lighting Circuit
•
• Take a padlock with you just in case and keep your tools locked
• Take a sharp knife such as an electricians knife sold by RS, Stanley knives or craft knives will not be permitted
• Fully understand the correct safe isolation procedure, make sure you keep the key in your pocket or locked away
• Know how to fault find, remember, continuity and insulation resistance tests are your friends
• Practice MIMS cable but leave it until the last task on the installation
• Practice doing back to back bends in steel conduit

Water heaters
As a general rule, any water heater over 15 litres should be fed by an independent circuit. Again, calculations should be made regarding the power consumption of the heating element although in most instances, it will be fed by a 16A protective device and 2.5mm2 cable.
OTHER CIRCUITS
Fire alarm
Introduced into the Building Regulations, specifically, Part B: Fire Safety, was the provision of a separate circuit for a fire alarm. It is thought that a separate circuit will not be isolated for any period of time hence the need to remove it from circuits such as lighting or socket outlet circuits.

 

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239- Inspection Testing & Certification of Electrical Installations Exam ( Old Notes )

The student must be aware of the correct use of terminology when answering questions, marks will be lost for incorrect use, some common examples include:
Using the term 'live' instead of 'phase'. Remember a live conductor includes the neutral also
Using the term 'completion certificate' instead of Electrical Installation Certificate
Using the term 'electrical inspection certificate' instead of Electrical Installation Certificate
Using the term 'initial' inspection certificate' instead of Electrical Installation Certificate
Using the term 'minor works certificate' instead of Minor Electrical Installation Works Certificate
Using the term 'Periodic Inspection Certificate' instead of 'Periodic Inspection Report for an Electrical Installation'
Incorrect use of the terms used to describe the 'Earthing Conductor' and Main Equipotential Bonding Conductors' For example using the incorrect term 'Main Bonding Conductor' instead of 'Earthing Conductor' and using the incorrect term 'Earth Bonding Conductor or even Bonding Conductor' instead of Main Equipotential Bonding Conductor
Incorrectly describing the 'Continuity of protective conductors' or 'Continuity of Ring Final Conductors' test as 'Open Loop' test when describing how to obtain R1 + R2
Incorrectly referring to 'Inspection Schedule' instead of 'Schedule of Inspections'
Incorrectly referring to 'Schedule of Tests' or Test Results Schedule instead of ' Schedule of Test Results'
It may sound petty, but you must learn to use the correct terms or you will lose marks - All the available past exam papers and the periodic inspection report check-list describe the correct terms to use
Naming documentation
When requested the documentation to complete during an initial or periodic inspection, many candidates will mention the Electrical Installation Certificate or the Periodic Inspection Report but forget to mention the 'Schedule of Inspections' and Schedule of Test Results'
Completing documentation
Many of the latest written exam papers include the requirement to complete an Electrical Installation Certificate or Periodic Inspection Report along with the accompanied 'Schedule of Inspections' and Schedule of Test Results' Often the question only asks the candidate to complete the schedule of test results for say a new ring final circuit. Many candidates waste valuable time and lose marks by completing the schedule of test results for every circuit given in the specification in part B of the question paper.
BIG TIP: READ THE QUESTION CAREFULLY:
Many candidates continue to get the value of Zs wrong for the circuit in question in part B of the exam. Check out my
A common error when completing questions involving schedule of test results is to forget to indicate functional tests have been performed and found satisfactory/unsatisfactory. To tick the tick box when completing details of ring final circuits, ensuring to indicate continuity of ring final conductors have been performed.
Failure to record the type of earthing system, i.e. TN-S, TN-C-S, TT,
Failure to record the value of Ze, PFC, Nominal voltage, Nominal frequency, are common errors.


Test procedures
A very common question is to explain in detail how to perform an insulation resistance test, often on a lighting circuit. Candidates regularly fail to state the instrument used which is an 'Insulation Resistance Ohm-meter' (Not a Megger! You will not gain any marks if you answer a Megger) Many candidates fail to identify the test voltage required for typical 230/240 volt installation which is 500 volts and the acceptable test value which is 0.5 Meg-ohm or greater (again due to change under 17th edition to a minimum acceptable value of 1.0 Meg-ohm) City and Guilds usually deliberately pick a lighting circuit that is stipulated as having two way switching, just to see if the candidate mentions to test the strappers in BOTH positions.
Failure to mention testing the insulation resistance of both strappers will lose you marks. Be warned!
Candidates regularly make mistakes when answering RCD questions. Often the question or specifications usually given in part B will make reference to a specific type of RCD for example a 30 mA RCD. Candidates are then asked to state the actual test current applicable to test this type of RCD. Candidates regularly incorrectly state the answer as x1/2 x1 and x5 instead of x1/2 = 15mA x1 = 30mA and x5 = 150mA
A frequent question which often occurs requires the candidate to explain how to perform a continuity test on a ring final circuit and to explain how R1 + R2 for the circuit is obtained. Many candidates regularly continue to get this procedure wrong check out my past exam papers and the Periodic Inspection Report check-list for a thorough explanation on how to perform these tests.
In the March 2007 paper -&- point out many exam candidates still cannot list the correct sequence of tests for a given scenario. One such scenario involves the testing of a lighting circuit, many candidates just listed the typical sequence including continuity or ring final circuit conductors, clearly they received 'Nil Pwa' for their effort
Many candidates could not correctly perform calculations involving the 'rule of thumb' or incorrectly applied the rule to the 'Measured' values instead of the 'Tabulated' values
On questions regarding insulation resistance, some candidates thought 0.00 Meg-ohms was an open circuit. Many candidates could not correctly describe the procedure for performing an external phase-earth fault loop impedance test. C&G are now requesting much more detail to such questions as well as RCD testing, requesting not only details of how to perform an RCD test but circuit preparation before hand as well as reasons why circuit preparation is required. See my March 2007 specimen paper for answers to all these questions including full colour diagram of how to perform the Ze test
October 2007 exam, part B scenario gave many candidates a difficult time. Here you were presented with a TN-C-S system installed in a domestic property, and an underground supply cable is being used to supply an external outhouse. However the electricity supply company will not allow you to use their means of earthing for the outhouse. So how do you provide a means of earthing for the outhouse? Where do you earth the supply cable? What checks must you make on the underground supply cable? Why can't you use the main house TN-C-S system as a means of earthing the outhouse? Many candidates have written to me seeking clarification on the part B scenario questions.
October 2007 Part B scenario
Solution to terminating the underground SWA supply cable
The above diagram is how the -&-'s question may lead you to terminate the SWA of the underground supply cable, since the question informs you. "You are NOT allowed to use the supply companies earthing system as a means of earthing the outhouse" However -&-'s mention nothing about earthing the supply cable itself. It is difficult to decide whether -&-'s are just testing the candidates knowledge of this situation VERY thoroughly or alternatively offering a red-herring to mislead the unwary candidate. Whichever is the reason for this question, it caused many exam candidates a great deal of difficulty and lost time trying to decide what the solution was.
The actual solution stems from BS 7671 regulation 542-01-09 part of this reg states
"If the protective conductor (i.e. the swa) forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device" This therefore has to be the main house end. See the only possible solution below

 

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But where manufactures recommend a method regulation 134.1.1 comes into play with:- Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.

As if this should over ride regulations like 531.2.8 Where an RCD is used for fault protection with, but separately from, an overcurrent protective device, it shall be verified that the residual current operated device is capable of withstanding, without damage, the thermal and mechanical stresses to which it is likely to be subjected in the case of a fault occurring on the load side of the point at which it is installed. Is of debate but I can see anyone forcing you to change to all RCBO after a multi RCD board it fitted and in any case if going through building control direct you have to submit plans first so any objection would be before the work started.

Multi-RCD are required to comply with:-
314.1 Every installation shall be divided into circuits etc. ( only showing part of reg )
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.
531.2.4 An RCD shall be so selected and the electrical circuits so subdivided that any protective conductor current which may he expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.

As I read it unless emergency lighting is used then lights should have there own RCD and not shared with any other circuit. The same would apply to fire alarm systems. Items like cookers which could cause other circuits to trip due to high earth leakage and sockets, likely used outside, should not really be on the same RCD as other items in the house. This could also apply to computer supplies.


“ Instructed person “
A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.:
“ Ordinary person “
A person who is neither a skilled person nor an instructed person.:

“ Wiring Systems “
To conform with the requirements of BS 7671, wiring systems must utilise cables complying with the relevant requirements of
the applicable British Standard or Harmonised Standard.
Alternatively, if equipment complying with Alternatively, if equipment complying with based on an IEC Standard is
to be used, the designer or other person responsible for specifying the installation must verify that any differences between that
standard and the corresponding British Standard or Harmonised Standard will not result in a lesser degree of safety than
that afforded by compliance :
A new series of Regulations ( 522.6.6 - 522.6.8 ) have been introduced in the 17th Edition of the IEE Wiring Regulations
concerning cables concealed in a wall or partition. These new Regulations introduce the concept of skilled person, instructed
person and ordinary person :
“ RCD Protection “
It is now a requirement to protect cables concealed in a wall or partition (at a depth of less than 50 mm) by a 30mA RCD where the
installation is not intended to be under the supervision of a skilled or instructed person where other methods of protection, including the
use of cables with an earthed metallic covering, earthed conduit/trunking or mechanical protection, can not be employed.
Irrespective of the depth, a cable in a partition where the construction includes metallic parts other than fixings shall be protected by
a 30 mA RCD. For example, this means that in a domestic installation, where insulated and sheathed cables are concealed in a
wall at a depth of less than 50 mm and have no mechanical protection, they need to be installed within the safe zones and protected
by a 30 mA RCD.
“ Skilled person “
A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create :

 

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Permitted cable routes :

with the British Standard. The effect of environmental conditions and general characteristics around various parts of the installation must be assessed to enable suitable electrical equipment, including the wiring system, to be specified.
For example, cables and equipment used in agricultural and horticultural premises should be installed away from areas or routes used by
animals or be of a type to withstand such attack. Any part of the fixed installation which may be exposed to a severe impact
must be able to survive it. In workshops, for example, where heavy objects are moved, installation of wiring systems in traffic
routes should be avoided or localised protection must be provided. Therefore, when designing a concealed installation, the designer
must select a suitable wiring system. Under the 17th Edition, depending on the type of wiring selected, the method of installation
and whether the installation will be under the control of a skilled person, or instructed person or ordinary person will depend
whether the concealed wiring will require RCD protection or not. For example, in a domestic installation, where insulated and sheathed
cables are concealed in a wall at a depth of less than 50 mm and have no mechanical protection, they need to be installed within
the safe zones and need to be protected by a 30 mA RCD. Regulations 522.6.6 and 522.6.8 are reproduced here for information.
522.6.6 A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition shall:
(i) incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective
conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or
(ii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a
protective conductor, or (iii) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the
requirements of these Regulations for a protective conductor, or (iv) be mechanically protected against damage sufficient to prevent
penetration of the cable by nails, screws and the like, or (v) be installed in a zone within 150 mm from the top of the wall or partition or
within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point,
accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to
the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined from the reverse
side, a zone formed on one side of a wall of 100 mm thickness or less or partition of 100 mm thickness or less extends to the reverse side.
522.6.7 Where Regulation 522.6.6 applies and the installation is not intended to be under the supervision of a skilled or instructed
person, a cable installed in accordance with Regulation 522.6.6 (v), and not complying with Regulation 522.6.6 (i), (ii), (iii) or (iv),
shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.
522.6.8 Irrespective of the depth of the cable from a surface of the wall or partition, in an installation not intended to be under the
supervision of a skilled or instructed person, a cable concealed in a wall or partition the internal construction of which includes metallic parts, other than metallic fixings such as nails, screws and the like, shall:
(i) incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective
conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846,
BS EN 60702-1 or BS 8436, or (ii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of
these Regulations for a protective conductor, or (iii) be enclosed in earthed trunking or ducting complying with BS EN 50085
and satisfying the requirements of these Regulations for a protective conductor, or (iv) be mechanically protected sufficiently to
avoid damage to the cable during construction of the wall or partition and during installation of the cable, or (v) be provided with
additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.
NOTE: If the cable is installed at a depth of 50 mm or less from the surface of a wall or partition the requirements of Regulation
522.6.6 also apply. RCD Protection ,An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors. In the case of a single-phase circuit, the device monitors the difference in currents
between the line and neutral conductors. If a line to earth fault develops, a portion of the line conductor current
will not return through the neutral conductor. The device monitors this difference, operates and disconnects the circuit when the residual current reaches a preset limit, the residual operating current (IΔn). An RCD on its own does not provide protection against overcurrents. Overcurrent protection is provided by a fuse or a circuit-breaker. However, combined RCD and circuit-breakers are available and are designated RCBOs. Unwanted tripping Unwanted tripping of RCDs can occur when a protective conductor current or leakage
current causes unnecessary operation of the RCD. An RCD must be so selected and the electrical circuits so subdivided that any
protective conductor current that may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device. Discrimination Where two, or more, RCDs are connected in series, discrimination must be
provided, if necessary, to prevent danger. During a fault, discrimination will be achieved when the device electrically nearest to the
fault operates and does not affect other upstream devices. Discrimination will be achieved when ‘S’ (Selective) types are used in conjunction with downstream general type RCDs. The ‘S’ type has a built-in time delay and provides discrimination by simply ignoring the fault for a set period of time allowing more sensitive downstream devices to operate and remove the fault. For example, when
two RCDs are connected in series, to provide discrimination, the first RCD should be an ‘S’ type. RCDs with built in time
delays should not be used to provide personal protection. Labelling Regulation 514.12.2 requires that where an installation incorporates an RCD a notice shall be fixed in a prominent position at or near the origin of the installation. The Regulation requires that the notice
shall be in indelible characters not smaller than illustrated in BS 7671, see fig. 4. Testing Refer to Regulations 612.8.1,
612.13.1 and 415.1.1 for requirements in terms of verification of installed RCDs.
“ Conclusion “ 1
Under the 17th Edition designers will now have to determine from the client whether the installation is going to be under the
supervision of a skilled person, instructed person or ordinary person.

Labelling requirement of 514.12.2

 

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Recognised devices ( Remember that BS- is Old / but still in Use )
RCDs are manufactured to harmonised standards and can be identified by their BS EN numbers. An RCD found in an
older installation may not provide protection in accordance with current standards. The following list identifies the applicable current standards:
BS 4293 : 1983 (1993) Specification for residual current operated circuit-breakers. (Replaced by BS EN 61008-1: 1995,
BS EN 61008-2-1: 1995 and BS IEC 61008-2-2: 1990). This Standard remains current :
BS 7071 : 1992 (1998)
Specification for portable residual current devices :
BS 7288 : 1990 (1998)
Specification for socket-outlets incorporating residual current devices. (SRCDs)
BS EN 61008-1 : 1995 (2001)
Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCBs)
BS EN 61009-1 : 2004
Residual current operated circuit-breakers with integral overcurrent protection for household and similar uses (RCBOs)
Characteristics of RCDs
RCDs are defined by a series of electrical characteristics, three main characteristics are:
1. The rating of the device in amperes, ( I ) :
2. The rated residual operating current of the protective device in amperes, I∆n:
3. Whether the device operates instantaneously or incorporates an intentional time delay to permit discrimination. Such devices are called ‘S’ or Selective :
Devices are manufactured with different values of rated current and rated residual operating current but we will just consider the rated residual operating current of the protective device in amperes, I∆n:
Discrimination
Where two, or more, RCDs are connected in series, discrimination must be provided, if necessary, to prevent danger (Regulation 531-2-9 refers). During a fault, discrimination will be achieved when the device electrically nearest to the fault operates and does not affect
other upstream devices. Discrimination will be achieved when ‘S’ (Selective) types are used in conjunction with downstream general
type RCDs. The ‘S’ type has a built-in time delay and provides discrimination by simply ignoring the fault for a set period of time allowing more sensitive downstream devices to operate and remove the fault. For example, when two RCDs are connected in series, to provide discrimination, the first RCD should be an ‘S’ type. RCDs with built in time delays should not be used to provide personal protection.
Testing
RCDs must be tested. The requirements are stated in the following Regulations:
The effectiveness of the RCD must be verified by a test simulating an appropriate fault condition and independent of any test facility, or
test button, incorporated in the device (Regulation 613-13-1)
Tests are made on the load side of the RCD between the phase conductor of the protected circuit and the associated cpc. Any load or appliances should be disconnected prior to testing. RCD test instruments require a few milliamperes to operate; this is
normally obtained from the phase and neutral of the circuit under test. When testing a three-phase RCD protecting a three-wire circuit, the instrument’s neutral is required to be connected to earth. This means that the test current will be increased by the instrument supply current and will cause some devices to operate during the 50% test, possibly indicating an incorrect operating time. Under this circumstance it is necessary to check the operating parameters of the RCD with the manufacturer before failing the RCD.
Integral Test Device ( Functional Testing ) 612.13
An integral test device is incorporated in each RCD. This device enables the mechanical parts of the RCD to be
verified by pressing the button marked ‘ T’ or ‘Test’ :
Test Instrument
The test instrument used to test RCDs should be capable of applying the full range of test current to an in-service
accuracy, as given in BS EN 61557-6. This in-service reading accuracy will include the effects of voltage
variations around the nominal voltage of the tester. To check RCD operation and to minimise danger during the test, the test current
should be applied for no longer than 2s. Instruments conforming to BS EN 61557-6 will fulfil the above requirements.
● “ OLD RCDs “
General Purpose RCDs to BS-4293 & Protected Sockets-Outlets BS-7288 :
( 240V – 50Hz – 80A – Load BS-4293 RCD ) ↔ ( BS-Number : Only = 200mS ) 50% of operating current : Device should Not Operate ;
100% of Operating current : Device should Operate in Less than 200mS :
Where the RCD incorporates an intentional time delay it should trip within a time range from 50% of the rated time delay plus 200ms’
to 100 % of the rated time delay plus 200ms
● “ NEW RCDs “
General Purpose RCBOs BS-EN 61009-1 ↔ ( BS-EN = Only 300mS )
General Purpose RCCBs BS-EN 61008-1 ( BS-EN 61008-1 : 230V ( 80A – 30mA – 230V )
50% of operating current Device should Not operate :
100% of operating current Device should operate in less than 300mS :
unless it is of ‘Type S’ (or selective) which incorporates an intentional time delay. In this case, it should trip within a time range from 130ms to 500ms ( Appendix 3 , page - 243 )
Additional Protection : Test current at 5 I∆n : I∆n ≤ 30mA / Device should Operate in Less than ( 40mS )

What is an RCD and what does it do? “ Definitions “ p / 29
An RCD is defined, in BS 7671, as: ‘A mechanical switching device or association of devices intended to cause the opening of the contacts when the residual current attains a given value under specified conditions’.

 

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“ 2392-10 “ 17th Edition of the IEE Wiring
Regulations on the 1st January 2008 has major implications for all electrical contractors, designers
and consultants. From 1st July 2008 all new electrical installations will have to be designed to comply with the new regulations : The biggest area of concern at present is the effect on an individual’s home being wired or re-wired.
there are five aspects that the 17th Edition identifies as requiring consideration for installations that are not under the supervision of skilled people (e.g. qualified electricians) or instructed people (e.g. facilities managers) – i.e. most domestic
installations,
● Socket outlets for general use in domestic installations must have the additional protection of an RCD Not exceeding 30mA (regulation 411.3.3 )
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA ( Regulation 701.411.3.3 )
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA ( Regulations 522.6.6–8 )
● To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD ( Regulation 314.1 )
● Separate circuits shall not be affected by the failure of other circuits ( Regulation 314.2 )
When designing the installation and selecting the correct assembly, the electrician will need to consider the above
five aspects, in accordance with the regulations. It is not solely the function of a particular consumer unit that has
one, two or three RCDs with an incomer isolator to solve the problem of meeting the 17th Edition regulations.
assembly to ensure that the installation complies with the 17th Edition regulations.
Everything starts ;
When designing an installation in a new build project, there are various options to consider, in order to satisfy
the requirements of the 17th Edition. For example, consider burying the cables more than 50mm into the
walls, or protect the cable with earthed metal, to remove the need for RCD protection. Once the wiring scheme has been finalised, the process of selecting how best to protect the circuits and the people can begin.
The regulations are open to interpretation, particularly regarding the division of installations, where acceptable levels of inconvenience resulting from a fault can be somewhat subjective. ( See page 11 for Regulations 314.1 and 314.2. )
● ( FCA ) Fully Compliant Assembly : ←
● ( PCA ) Partially Compliant Assembly : ←
● ( NCA ) Non-Compliant Assembly : potentially dangerous ; ←
to satisfy all aspects where an RCD has to be used for safety reasons but does not comply with all parts of regulation 314; a Non-Compliant Assembly is judged to satisfy neither safety aspects nor regulation 314. :
Customers are looking for a competitive offering, balanced with potential safety aspects and avoiding the
hazards and nuisance that a short circuit trip, overload condition or earth leakage may cause.
For “ example “ a consumer unit with an isolator and double RCD (see page 3 Example A) is often promoted as a way of meeting the 17th Edition regulations on the basis that every circuit is protected by an RCD, and the circuits split evenly between two RCDs. However, in the event of a fault on either set of MCBs, the RCD may trip as well. This creates an unwanted disconnection of the MCBs where no fault exists (contrary to section 314.1) and also causes unwanted disconnection of other circuits ( contrary to section 314.2 ).
A dual RCD split load board will meet the 17th Edition requirements for the following: :
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not
exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA :
However, depending on the installation design, it is unlikely to satisfy the regulations on:
*To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD. )
* Separate circuits shall not be affected by the failure of other circuits. In the event of a fault on either set of MCBs, the RCD may trip as well. This creates an unwanted disconnection of the MCBs where no fault exists (contrary to section
314.1) and also causes unwanted disconnection of other circuits (contrary to section 314.2 ).
Prior to the 17th Edition, lights have not been part of the RCD circuit as they tend to trip the RCD whenever an incandescent bulb fails, for example, causing unacceptable nuisance. Having the lights in the same circuit may cause nuisance disconnection to any other circuit supplied on the RCD. In addition there is a smoke alarm and a light circuit
on the same RCD, so every time the light circuit trips (when a bulb fails) the house and the alarm circuit could be disabled, putting the occupants at risk of a fire not being detected. The safety implications of this configuration by not
addressing the requirements of section 314 make this a Non-Compliant Assembly :

● ( PCA ) Partially Compliant Assembly : ←
A split load board with independent RCBOs will meet the17th Edition requirements for the following:
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by
appropriate earthed metal, must be protected by an RCD not exceeding 30mA :

However, depending on the installation design, whilst this layout takes into account the danger arising from the
failure of a single circuit (such as lighting) it does not fully comply with :
* To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD.
* Separate circuits shall not be affected by the failure of other circuits :
It may be advisable to have a socket circuit on a separate circuit. In larger residential properties it would be advisable to separate the downstairs circuit or the kitchen circuit from the other circuits supplied by a sole RCD to ensure that in the event of a fault there would be at least one power circuit available. Prior to the 17th Edition, it was common to have all
socket power circuits supplied from one RCD with no account of the implications for safety or significant inconvenience being apparent. However, the increasing number of electronic devices now found in a home results in a greater amount of earth leakage current that may lead to a tripping of the RCD and fall foul of 531.2.4.
( Note Also depending on the wiring scheme the smoke detector may not need to be an RCBO. )

Main switch with RCBOs on all circuits : ● ( FCA ) Fully Compliant Assembly : ←


A standard main switch disconnector controlled consumer unit with RCBOs for every outgoing circuit instead of the usual MCBs, will fully comply with the 17th Edition regulations. A fault on any circuit will not impact on other circuits, and so all aspects of the regulations are satisfied.:
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA.
● To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD.
● Separate circuits shall not be affected by the failure of other circuits.

Main switch with RCBOs on critical circuits : ● ( FCA ) Fully Compliant Assembly : ←

By looking closely at the wiring scheme in an installation, the assembly can be made more cost effective by using MCBs to protect some circuits rather than RCBOs, without compromising compliance with the 17th Edition.
For example, at the point of cable entry to the consumer unit, incoming and outgoing cable runs are all encased in suitable ‘metal trunking’ or buried deeper than 50mm, so do not require RCD protection. As none of the cables are in the walls, the smoke alarms similarly do not require RCD protection. The burglar alarm system may have its own trunking or metal covering for the supply to the main control
console. If it does, and all the other devices are low voltage or cable runs in the ceiling, then this too could be MCB protected. This will depend on the wiring scheme employed for this ancillary piece of equipment. You could also decide that the immersion heater cable and cooker point (without socket) are in areas where they can be surface mounted and shrouded inside a short length of conduit, or buried deeper than 50mm in the wall.
This example illustrates that by analysing the wiring scheme, RCBOs can be replaced with MCBs, reducing the
costs whilst still providing a Fully Compliant Assembly ( FCA ).