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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 ,
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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