17th Edition

AWe keep power under control.

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PLS – Miniature Circuit Breakers

PKS – RCBOs

PFIM – RCDs

Moeller Consumer Units and the17th Edition Wiring Regulations

2 3

The introduction of the 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. The examples used in this brochure will help the electrical engineer to select the correct assembly. We use the term assembly as there are no specific consumer units that meet the 17th Edition – it is how the building is wired that dictates the components required, which in turn are assembled into a consumer unit.

Practically speaking, 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, but also some commercial installations. These are:

● 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.

The following pages will provide a practical guide to help you to select the components for an assembly to ensure that the installation complies with the 17th Edition regulations.

Everything starts from the wiring scheme

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.)

To this end, the following pages outline various consumer unit configurations that, dependent on the installation design, will offer a Fully Compliant Assembly ( FCA ) or Partially Compliant Assembly ( PCA ), or illustrate possible pitfalls making an installation potentially dangerous and so a Non-Compliant Assembly ( NCA ).

Note that the above terms indicate Moeller’s assessment of how a particular installation may comply with the regulations: a Partially Compliant Assembly has been judged by Moeller 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). Many manufacturers are promoting the dual RCD board as a fully compliant solution; however compliance is dependent on the design of the installation and at best this will only be a Partially Compliant Assembly.

You can find examples of Fully Compliant Assemblies on pages 5 and 6.

Introduction

2 3

Dual RCD split load board

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.

6AMCB

6AMCB

6AMCB

32AMCB

6AMCB

32AMCB

32AMCB

40AMCB

RCD RCD MAINISOLATOR

smoke

alar

ms

upstairs

lights

outside l

ights

shower

downstairs

and

bathro

om lig

hts

upstairs

sock

ets

downstairs

sock

ets

cooke

r

Example A

NCA

Example ADual RCD split load board

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.

4 5

Split load board with independent RCBOs

A split load board with independent RCBOs will meet the 17th Edition requirements for the following:




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:



Example B

32AMCB

32AMCB

32AMCB

40AMCB

6ARCBO

6ARCBO

6ARCBO

6ARCBO

RCD MAINISOLATOR

shower

upstairs

sock

ets

downstairs

sock

ets

cooke

r

outside l

ights

upstairs

lights

downstairs

and

bathro

om lig

hts

smoke

alar

ms PCA

Example BSplit load board with independent RCBOs

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.

4 5

Example C

Main switch with RCBOs on all circuits

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.






6ARCBO

6ARCBO

6ARCBO

6ARCBO

MAINISOLATOR

shower

upstairs

sock

ets

downstairs

sock

ets

cooke

r

imm

ersio

n hea

ter

upstairs

lights

downstairs

and

bathro

om lig

hts

smoke

alar

ms

16ARCBO

32ARCBO

32ARCBO

40ARCBO

40ARCBO

burglar

alar

m FCA

Example CMain switch with RCBOs on all circuits

6 7

Example D

Main switch with RCBOs on critical circuits

By looking closely at the wiring scheme in an installation, the assembly in Example C 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

6AMCB

6AMCB

6ARCBO

6ARCBO

MAINISOLATOR

shower

upstairs

sock

ets

downstairs

sock

ets

cooke

r

imm

ersio

n hea

ter

upstairs

lights

downstairs

and

bathro

om lig

hts

smoke

alar

ms

16AMCB

32ARCBO

32ARCBO

40ARCBO

40AMCB

burglar

alar

m FCA

Example DMain switch with RCBOs on critical circuits

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).

6 7

Example E

By reviewing the wiring scheme employed with the split load assembly proposed in Example B, the cost of the finished assembly can be reduced, and partial compliance with the regulations achieved.

The split load board laid out here will meet the 17th Edition requirements for the following:




However, depending on the installation design, it is unlikely to satisfy the regulations on:



32AMCB

32AMCB

40AMCB

RCD MAINISOLATOR

shower

upstairs

sock

ets

downstairs

sock

ets

cooke

r

imm

ersio

n hea

ter

upstairs

lights

downstairs

and

bathro

om lig

hts

smoke

alar

ms

6ARCBO

6ARCBO

6AMCB

6AMCB

16AMCB

burglar

alar

m

40AMCB

PCA

Example ESplit load board with RCBOs on critical circuits

With this example there is still the risk of one circuit failure impacting on another (regulation 314.2); however the level of inconvenience could be considered to be acceptable (only the sockets and showers are affected), and no hazard or safety issues are inherent. Again, the installer will need to consider the amount of leakage in the installation, due to electronic devices in the house, and it may be a consideration to split the power sockets and have one of them on an RCBO.

The end result is that no base consumer unit exists that complies with the 17th Edition. The choice of consumer unit and the configuration of devices within it can only be made after the wiring scheme has been finalised.

Split load board with RCBOs on critical circuits

8 9

2-Pole · 100A Main Switch Controlled

Outgoing Ways Dimensions (mm) Width Height Depth Part Number

2 172 225 111 BC-P2

6 244 225 111 BC-P6

10 316 225 111 BC-P10

12 351 225 111 BC-P12

18 457 225 111 BC-P18

2-Pole · RCD Controlled

Type Outgoing Ways RCD Rated Current In (A) Dimensions (mm) Width Height Depth Part Number

30mA RCD-controlled 2 40 172 225 111 BC-P2R40

2 63 172 225 111 BC-P2R63

6 63 244 225 111 BC-P6R63

6 80 244 225 111 BC-P6R80

6 100 244 225 111 BC-P6R100

10 63 316 225 111 BC-P10R63

10 80 316 225 111 BC-P10R80

10 100 316 225 111 BC-P10R100

12 63 351 225 111 BC-P12R63

12 80 351 225 111 BC-P12R80

12 100 351 225 111 BC-P12R100

18 80 457 225 111 BC-P18R80

18 100 457 225 111 BC-P18R100

100mA time-delayedRCD (Type G)

12 100 351 225 111 BC-P12R100G

18 100 457 225 111 BC-P18R100G

Split Load · 2-Pole · 100A Main Switch / 30mA RCD Controlled

Outgoing Ways RCD Ways Available* RCD Rated Current In (A) Dimensions (mm) Width Height Depth Part Number

8 1–7 63 316 225 111 BC-P8SR63

8 1–7 80 316 225 111 BC-P8SR80

10 1–9 63 351 225 111 BC-P10SR63

10 1–9 80 351 225 111 BC-P10SR80

16 1–15 80 457 225 111 BC-P16SR80

Note * number of freely configurable RCD protected ways.

Dual RCD · Split Load · 100A Main Switch / 30mA RCD Controlled


14 1–14 63 + 63 457 225 111 BC-P14SR63R63

14 1–14 80 + 63 457 225 111 BC-P14SR80R63

14 1–14 80 + 80 457 225 111 BC-P14SR80R80


Toggle Colours2 A 4 A 6 A 10 A 13 A 16 A

20 A 25 A 32 A 40 A 50 A 63 A

XBoard Consumer UnitsInsulated

8 9

2-Pole · 100A Main Switch Controlled

Outgoing Ways Dimensions (mm) Width Height Depth Part Number

2 180 223 113 BC-M2

6 252 223 113 BC-M6

10 324 223 113 BC-M10

12 359 223 113 BC-M12

18 465 223 113 BC-M18

2-Pole · RCD Controlled

Type Outgoing Ways RCD Rated Current In (A) Dimensions (mm) Width Height Depth Part Number

30mA RCD-controlled 2 40 180 223 113 BC-M2R40

2 63 180 223 113 BC-M2R63

6 63 252 223 113 BC-M6R63

6 80 252 223 113 BC-M6R80

6 100 252 223 113 BC-M6R100

10 63 324 223 113 BC-M10R63

10 80 324 223 113 BC-M10R80

10 100 324 223 113 BC-M10R100

12 63 359 223 113 BC-M12R63

12 80 359 223 113 BC-M12R80

12 100 359 223 113 BC-M12R100

18 80 465 223 113 BC-M18R80

18 100 465 223 113 BC-M18R100

100mA time-delayedRCD (Type G)

12 100 359 223 113 BC-M12R100G

18 100 465 223 113 BC-M18R100G

Split Load · 2-Pole · 100A Main Switch / 30mA RCD Controlled


8 1–7 63 324 223 113 BC-M8SR63

8 1–7 80 324 223 113 BC-M8SR80

10 1–9 63 359 223 113 BC-M10SR63

10 1–9 80 359 223 113 BC-M10SR80

16 1–15 80 465 223 113 BC-M16SR80


Dual RCD · Split Load · 100A Main Switch / 30mA RCD Controlled


14 1–14 63 + 63 465 223 113 BC-M14SR63R63

14 1–14 80 + 63 465 223 113 BC-M14SR80R63

14 1–14 80 + 80 465 223 113 BC-M14SR80R80



20 A 25 A 32 A 40 A 50 A 63 A

XBoard Consumer UnitsMetal

10 11

Miniature Circuit Breakers · single-pole · 6kA

Rated Current In (A) B Curve C Curve

2 PLS6-B2 PLS6-C2

6 PLS6-B6 PLS6-C6

10 PLS6-B10 PLS6-C10









Combined RCD/MCB (RCBO) · single-pole + Neutral · conditionally surge current proof 250A · B & C curve · type AC

Rated Current In (A) Type / Tripping CurrentB Curve · 30mA B Curve · 100mA C Curve · 30mA C Curve · 100mA

6 PKS6-6/1N/B/003 PKS6-6/1N/B/01 PKS6-6/1N/C/003 PKS6-6/1N/C/01








Main Incoming Switch · 2-Pole · 10kA

Rated Current In (A) Part Number

63 IS-63/2

80 IS-80/2

100 IS-100/2

125 IS-125/2

Outgoing Devices

Incoming Devices

XBoard Consumer UnitsIncoming and Outgoing Devices


20 A 25 A 32 A 40 A 50 A 63 A

Standard AC RCDs · 2-Pole

Rated Current In (A) Tripping Current30mA 100mA 300mA 500mA

16 * PFIM-16/2/001 – – –

25 PFIM-25/2/003 PFIM-25/2/01 PFIM-25/2/03 PFIM-25/2/05





Note * 16 A RCD is rated for 10mA earth leakage.

10 11Key Extractsfrom 17th Edition Regulations

Note: There are exceptions when the socket outlets are used by skilled or instructed persons, but not relevant in residential property. For example 411.3.3 relates to socket outlets located anywhere in a home, including the socket in the cooker outlet. However RCD protection for the cooker outlet is required if any of the cables are buried in the wall and not deeper than 50mm, as indicated in 522.6.

Part 5 Requirements for protecting cable against impact

This will often result in the need for additional RCD protection. This is covered in 522.6.6, 522.6.7 and 522.6.8 and can be summarised as follows:All circuits buried in a wall or partition at less than 50mm depth and without mechanical protection require RCD protection.

Key extracts from 17th Edition of the IEE Wiring Regulations BS 7671 : 2008

314 Division of Installation

314.1 Every installation shall be divided into circuits, as necessary, to (i) avoid hazards and minimize inconvenience in the event of a fault(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.

411.3.3 Additional protection

In a.c. systems, additional protection by means of an RCD in accordance with Regulation 415.1 shall be provided for:(i) socket-outlets with a rated current not exceeding 20A that are for use by ordinary persons and are intended for general use.

Section 701 Locations containing a bath or shower

701.411.3.3 Additional protection by RCDs

Additional protection shall be provided for all circuits of the location, by the use of one or more RCDs having the characteristics specified in Regulation 415.1.1 (30mA RCD)

531.2.4 An RCD shall be so selected and the electrical circuits so sub divided that any protective conductor current which may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.

Note: see regulations 314.1 and 531.2.4.

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Extracts printed with permission of The Institute of Engineering and Technology.

12

AWe keep power under control.

Moeller Electric LimitedPO Box 35, Gatehouse CloseAylesburyBuckinghamshire HP19 8DH

Direct sales ordering and technical supporttel 01296 397400fax 01296 392413email [email protected] [email protected]

© Moeller Electric Limited 05/08T0200-276GB

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