Reg 411.3.3

[highspark]

Got a small job to put an extra socket in supplying tumble drier. If I label it as tumble drier only, can I omitt RCD protection? Is a FCU required aswell as the socket outlet?

Also I have a request to fit spots on a dimmer in bathroom. The dimmer is outside zone 2. Is it permitted inside a bathroom or will it have to be installed outside?

 

[Richard Burns]

OK I am voted down here on the metallic sheath / CPC properties of the sheath, I had better go back and redo one of my jobs!

The consideration I had is that although the screen is very thin it is around the whole diameter of the cable and it is greater in csa than the size required for a cpc even taking into account the reduced conductivity of aluminium. e.g for 1mm2 two core and earth FP200 the copper equivalent csa of the sheath is 1.4mm2.

 

[Plonker 3]

OK I am voted down here on the metallic sheath / CPC properties of the sheath, I had better go back and redo one of my jobs!

The consideration I had is that although the screen is very thin it is around the whole diameter of the cable and it is greater in csa than the size required for a cpc even taking into account the reduced conductivity of aluminium. e.g for 1mm2 two core and earth FP200 the copper equivalent csa of the sheath is 1.4mm2.

The big query is, is the sheath permanently in contact with the CPC, which I don't believe the manufacturers say it is.

 

[Richard Burns]

Hmm permanently in contact not sure but the extract from the spec given above states

Screen

The screen shall consist of a longitudinally applied laminated aluminium tape, of minimum metal thickness 0.075mm, securely bonded to the sheath.

An uninsulated tinned copper circuit protective conductor shall be in contact with the screen.

​

which tells you it is in contact but does not state permanently.

 

[Plonker 3]

Which is why MIMS and SWA is classed as that when glanded correctly, and I also believe there is a Twin & Earth version too which which meets the requirements of the BGB

 

[Deleted member 26818]

He seems to have opinions that make better sense than some of the regs

I changed my mind about rcd sockets on an installation where no rcd exists,I now take side with spinlondons view
The "whole circuit" should have rcd protection,not just the extra bit installed

I have always done this but now believe its the only way it should be done( the word needs ommitted by the way)

I think you may be misunderstanding my view.
The Regulations only require RCD protection to "whole circuits", when the circuits are of a special location.
So if you were to spur off a RFC to feed a towel rail in a bathroom, the RFC would require RCD protection, using an RCD FCU would not (to my mind) be acceptable.
Socket-outlets don't in them selves require RCD protection, unless they are used to supply mobile equipment outdoors, or they are for use by ordinary persons, and are intended for general use.
A socket-outlet for use by an ordinary person, that is intende to be used by a specific item of equipment as in this cas a washingmachine, does not require RCD protection.
However the new cabling might as pointed out by highspark and biff55.
Unfortunately FP200 is not an acceptable cable.
SWA or Flexishield (or similar) are acceptable.

 

[brman]

I think you may be misunderstanding my view.
The Regulations only require RCD protection to "whole circuits", when the circuits are of a special location.
So if you were to spur off a RFC to feed a towel rail in a bathroom, the RFC would require RCD protection, using an RCD FCU would not (to my mind) be acceptable.
Socket-outlets don't in them selves require RCD protection, unless they are used to supply mobile equipment outdoors, or they are for use by ordinary persons, and are intended for general use.
A socket-outlet for use by an ordinary person, that is intende to be used by a specific item of equipment as in this cas a washingmachine, does not require RCD protection.
However the new cabling might as pointed out by highspark and biff55.
Unfortunately FP200 is not an acceptable cable.
SWA or Flexishield (or similar) are acceptable.

I can see what you mean on that bit but I interpret it differently. First, if the aim of the regs is to ensure better protection in bathrooms then that is covered fine by a RCD FCU. Adding RCD protection to the rest of the ring might be useful but it doesn't have any real affect on the special location being protected.
Then there is the wording in the regs: 701.411.3.3 "additional protection shall be provided for all low voltage circuits of the location, by the use of one or more RCDs....."
I can see this can be interpreted as "whole circuits" but it doesn't actually say so. If I added an FCU spur to a bathroom I would consider the "circuit of the location" to be from the FCU onwards, particular as the FCU is not only RCD protection but the protective device for that circuit.

Bottom line is that I still reckon a RCD FCU is a good alternative to a new CU if you are modifying an old installation.

I just know you will now point out the flaw in my argument........

 

[Deleted member 26818]

An RCD will only detect faults downstream.
It will not detect faults upstream.
As such, in the example I gave, any earth fault current caused by a fault on the RFC will bypass the RCD and enter the special location.
As to the wording, why should it state "whole circuits"?
Why would the word circuit require a qualifier to let us know that it refers to the whole circuit?
Surely if anything would need qualyfing, it would be when only a part of a circuit is refered to?
As to the FCU being the origin of the circuit, that doesn't appear to be what Appendix 15 states.
Then of course, there's the requirement of 314.4: "Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated."
I accept that the part of the circuit from the FCU, satisfies the definition of a circuit, as it would be "an assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).
However, unless you wish to argue either that it is not a final circuit, or that an FCU is a DB, it will not meet the requirements of Reg. 314.4, insofar is it is not connected to a separate way in a DB.
It can be argued, that 701.411.3.3, doesn't just refer to circuits that supply equipment in the location, but also to circuits that pass through the location concealled in the walls or above the ceilings.

 

[brman]

An RCD will only detect faults downstream.
It will not detect faults upstream.
As such, in the example I gave, any earth fault current caused by a fault on the RFC will bypass the RCD and enter the special location.
As to the wording, why should it state "whole circuits"?
Why would the word circuit require a qualifier to let us know that it refers to the whole circuit?
Surely if anything would need qualyfing, it would be when only a part of a circuit is refered to?
As to the FCU being the origin of the circuit, that doesn't appear to be what Appendix 15 states.
Then of course, there's the requirement of 314.4: "Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated."
I accept that the part of the circuit from the FCU, satisfies the definition of a circuit, as it would be "an assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).
However, unless you wish to argue either that it is not a final circuit, or that an FCU is a DB, it will not meet the requirements of Reg. 314.4, insofar is it is not connected to a separate way in a DB.
It can be argued, that 701.411.3.3, doesn't just refer to circuits that supply equipment in the location, but also to circuits that pass through the location concealled in the walls or above the ceilings.

can't fault your logic (as usual!) but I think that the bottom line for me is, if doing any work in a bathroom, would I change the consumer unit to add an RCD or add an RCD FCU? For me there is a enough ambiguity in the regs to allow that the latter is a sensible compromise. Same as fitting an outside socket with an RCD rather RCD on the whole circuit which, although the regs don't require it, would make it safer.

 

[jdd]

Not so sure about the dimmer advice mate. Just cuz it's not in zone 2, doesn't mean it's compliant. It's got to be suitable for the location (512.2.1)