Moeller Consumer Units and the 17th Edition Wiring Regulations

The introduction of the 17

Edition of the IEE Wiring

Regulations on the 1

January 2008 has major

implications for all electrical contractors, designers
and consultants. From 1

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 17

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 17

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 17

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 17

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 17

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 17

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

Dual RCD split load board

A dual RCD split load board will meet the 17

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.

MCB

32A

MCB

32A

MCB

32A

MCB

40A

MCB

RCD

MAIN

ISOLATOR

smoke alarms

upstairs lights

outside lights

shower

downstairs and

bathr

oom lights

upstairs sockets

downstairs sockets

cooker

Example A

NCA

Example A

Dual 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 17

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.

Split load board with independent RCBOs

A split load board with independent RCBOs will meet the
17

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.

Example B

32A

MCB

32A

MCB

32A

MCB

40A

MCB

RCBO

RCD

MAIN

ISOLATOR

shower upstairs sockets

downstairs sockets

cooker

outside lights

upstairs lights

downstairs and

bathr

oom lights

smoke alarms

PCA

Example B

Split 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 17

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.

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
17

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.

RCBO

MAIN

ISOLATOR

shower

upstairs sockets

downstairs sockets

cooker

immersion heater

upstairs lights

downstairs and

bathr

oom lights

smoke alarms

16A

RCBO

32A

RCBO

32A

RCBO

40A

RCBO

40A

RCBO

burglar alarm

FCA

Example C

Main switch with RCBOs on all circuits

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
17

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

MCB

RCBO

MAIN

ISOLATOR

shower

upstairs sockets

downstairs sockets

cooker

immersion heater

upstairs lights

downstairs and

bathr

oom lights

smoke alarms

16A

MCB

32A

RCBO

32A

RCBO

40A

RCBO

40A

MCB

burglar alarm

FCA

Example D

Main 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).

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

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.

32A

MCB

32A

MCB

40A

MCB

RCD

MAIN

ISOLATOR

shower upstairs sockets

downstairs sockets

cooker

immersion heater

upstairs lights

downstairs and

bathr

oom lights

smoke alarms

RCBO

MCB

16A

MCB

burglar alarm

40A

MCB

PCA

Example E

Split 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 17

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

2-Pole · 100A Main Switch Controlled

Outgoing Ways

Dimensions (mm)

Width Height Depth

Part Number

172

225

111

BC-P2

244

225

111

BC-P6

316

225

111

BC-P10

351

225

111

BC-P12

457

225

111

BC-P18

2-Pole · RCD Controlled

Type

Outgoing Ways

RCD Rated Current I

(A)

Dimensions (mm)

Width Height Depth

Part Number

30mA RCD-controlled

172

225

111

BC-P2R40

172

225

111

BC-P2R63

244

225

111

BC-P6R63

244

225

111

BC-P6R80

100

244

225

111

BC-P6R100

316

225

111

BC-P10R63

316

225

111

BC-P10R80

100

316

225

111

BC-P10R100

351

225

111

BC-P12R63

351

225

111

BC-P12R80

100

351

225

111

BC-P12R100

457

225

111

BC-P18R80

100

457

225

111

BC-P18R100

100mA time-delayed

RCD (Type G)

100

351

225

111

BC-P12R100G

100

457

225

111

BC-P18R100G

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

Outgoing Ways

RCD Ways Available* RCD Rated Current I

(A)

Dimensions (mm)

Width Height Depth

Part Number

1–7

316

225

111

BC-P8SR63

1–7

316

225

111

BC-P8SR80

1–9

351

225

111

BC-P10SR63

1–9

351

225

111

BC-P10SR80

1–15

457

225

111

BC-P16SR80

Note

* number of freely configurable RCD protected ways.

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

Outgoing Ways

RCD Ways Available* RCD Rated Current I

(A)

Dimensions (mm)

Width Height Depth

Part Number

1–14

63 + 63

457

225

111

BC-P14SR63R63

1–14

80 + 63

457

225

111

BC-P14SR80R63

1–14

80 + 80

457

225

111

BC-P14SR80R80

Note

* number of freely configurable RCD protected ways.

Toggle Colours

2 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 Units

Insulated

2-Pole · 100A Main Switch Controlled

Outgoing Ways

Dimensions (mm)

Width Height Depth

Part Number

180

223

113

BC-M2

252

223

113

BC-M6

324

223

113

BC-M10

359

223

113

BC-M12

465

223

113

BC-M18

2-Pole · RCD Controlled

Type

Outgoing Ways

RCD Rated Current I

(A)

Dimensions (mm)

Width Height Depth

Part Number

30mA RCD-controlled

180

223

113

BC-M2R40

180

223

113

BC-M2R63

252

223

113

BC-M6R63

252

223

113

BC-M6R80

100

252

223

113

BC-M6R100

324

223

113

BC-M10R63

324

223

113

BC-M10R80

100

324

223

113

BC-M10R100

359

223

113

BC-M12R63

359

223

113

BC-M12R80

100

359

223

113

BC-M12R100

465

223

113

BC-M18R80

100

465

223

113

BC-M18R100

100mA time-delayed

RCD (Type G)

100

359

223

113

BC-M12R100G

100

465

223

113

BC-M18R100G

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

Outgoing Ways

RCD Ways Available* RCD Rated Current I

(A)

Dimensions (mm)

Width Height Depth

Part Number

1–7

324

223

113

BC-M8SR63

1–7

324

223

113

BC-M8SR80

1–9

359

223

113

BC-M10SR63

1–9

359

223

113

BC-M10SR80

1–15

465

223

113

BC-M16SR80

Note

* number of freely configurable RCD protected ways.

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

Outgoing Ways

RCD Ways Available* RCD Rated Current I

(A)

Dimensions (mm)

Width Height Depth

Part Number

1–14

63 + 63

465

223

113

BC-M14SR63R63

1–14

80 + 63

465

223

113

BC-M14SR80R63

1–14

80 + 80

465

223

113

BC-M14SR80R80

Note

* number of freely configurable RCD protected ways.

Toggle Colours

2 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 Units

Metal

Miniature Circuit Breakers

· single-pole · 6kA

Rated Current I

(A)

B Curve

C Curve

PLS6-B2

PLS6-C2

PLS6-B6

PLS6-C6

PLS6-B10

PLS6-C10

PLS6-B13

PLS6-C13

PLS6-B16

PLS6-C16

PLS6-B20

PLS6-C20

PLS6-B25

PLS6-C25

PLS6-B32

PLS6-C32

PLS6-B40

PLS6-C40

PLS6-B50

PLS6-C50

PLS6-B63

PLS6-C63

Combined RCD/MCB (RCBO)

· single-pole + Neutral · conditionally surge current proof 250A · B & C curve · type AC

Rated Current I

(A)

Type / Tripping Current

B Curve · 30mA

B Curve · 100mA

C Curve · 30mA

C Curve · 100mA

PKS6-6/1N/B/003

PKS6-6/1N/B/01

PKS6-6/1N/C/003

PKS6-6/1N/C/01

PKS6-10/1N/B/003

PKS6-10/1N/B/01

PKS6-10/1N/C/003

PKS6-10/1N/C/01

PKS6-13/1N/B/003

PKS6-13/1N/B/01

PKS6-13/1N/C/003

PKS6-13/1N/C/01

PKS6-16/1N/B/003

PKS6-16/1N/B/01

PKS6-16/1N/C/003

PKS6-16/1N/C/01

PKS6-20/1N/B/003

PKS6-20/1N/B/01

PKS6-20/1N/C/003

PKS6-20/1N/C/01

PKS6-25/1N/B/003

PKS6-25/1N/B/01

PKS6-25/1N/C/003

PKS6-25/1N/C/01

PKS6-32/1N/B/003

PKS6-32/1N/B/01

PKS6-32/1N/C/003

PKS6-32/1N/C/01

PKS6-40/1N/B/003

PKS6-40/1N/B/01

PKS6-40/1N/C/003

PKS6-40/1N/C/01

Main Incoming Switch · 2-Pole · 10kA

Rated Current I

(A)

Part Number

IS-63/2

IS-80/2

100

IS-100/2

125

IS-125/2

Outgoing Devices

Incoming Devices

XBoard Consumer Units

Incoming and Outgoing Devices

Toggle Colours

2 A

4 A

6 A

10 A 13 A

16 A

20 A 25 A 32 A

40 A

50 A 63 A

Standard AC RCDs · 2-Pole

Rated Current I

(A)

Tripping Current

30mA

100mA

300mA

500mA

16 *

PFIM-16/2/001

–

PFIM-25/2/003

PFIM-25/2/01

PFIM-25/2/03

PFIM-25/2/05

PFIM-40/2/003

PFIM-40/2/01

PFIM-40/2/03

PFIM-40/2/05

PFIM-63/2/003

PFIM-63/2/01

PFIM-63/2/03

PFIM-63/2/05

PFIM-80/2/003

PFIM-80/2/01

PFIM-80/2/03

PFIM-80/2/05

100

PFIM-100/2/003

PFIM-100/2/01

PFIM-100/2/03

PFIM-100/2/05

Note

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

Key Extracts

from 17

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 17

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.

“

”

“

”

“

”

“

”

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