Residual Current Protection and all that!

[spongsdad]

My son, who lives in a 1960s bungalow is revamping the lounge. To this end, he wants to install two additional double sockets. His local electrical contractor has advised him that these sockets, and therefore the circuit to which they will be added require residual current protection. My understanding is that because this is an alteration to an existing circuit, RCD protection is not required. Am I correct? Nevertheless, my advice to him is very much to incorporate RCD protection.
Could anyone please suggest how this might best be accomplished. The options appear to be :1) RCD sockets (in my view not a particularly aesthetic solution) 2) RCBO for the circuit in the consumer unit . This option probably not possible given the age of the CU (which does however have MCBs rather than rewireable fuses.) 3) Install new CU. Would this 3rd option bring the whole installation within the scope of the 17th edition? I realise that the whole installation must be tested and certificated as a consequence of the fitting of a new CU.
Finally, what documentation should my son expect from the contractor upon completion of this work?
Thanks.

 

[echoes]

My understanding is that because this is an alteration to an existing circuit, RCD protection is not required. Am I correct?

No, but the first amendment coming soon will permit it if the designer is satisfied that there is 'no increased risk from the alteration or addition' (for instance if the sockets could be expected to supply outdoor equipment, then this exemption would not be satisfied).

As things stand, the new sockets must have RCD protection according to the usual requirements for socket circuits and cable installation method.

If you plan to upgrade the CU anyway, then maybe a new full size CU could be installed to supply this extended socket circuits with RCD protection, and then migrate the other circuits to it in due course.

Alternatively, RCD sockets, or an RCD FCU for the new sockets.
EDIT: Not RCD sockets - see below.

 

[Taylortwocities]

Alternatively, RCD sockets, or an RCD FCU for the new sockets.

Umm are you sure.
Putting in RCD sockets will satisfy the "could be used for equipment outdoors" issue
but it does not provide the (RCD) requirement to protect cables less than 50mm from the surface.

The upcoming amendment to BS7671 provides some flexibilty on the wiring issue, but right now its BS7671(2008) not amended and requires an RCD for the circuit.

 

[echoes]

Thanks TTC for that correction - Sorry - the RCD sockets would not satisfy the requirement to protect buried cables, so any new wiring would most likely have to be on the surface (probably not what you want). And an RCD FCU would need to be installed such that no new buried cables are run to supply it (e.g. by installing it adjacent to an existing outlet).

It may well be considerably easier/quicker for the RCD protection for the whole circuit to be provided by an RCD in a CU, and this would allow any further additions on that circuit to benefit from RCD protection.

 

[spongsdad]

Thanks for replies so far. Let me make sure I have understood correctly. An alteration to an existing circuit brings all of that circuit within the remit of the 17th edition. Is that correct? Therefore, it will be necessary to protect that circuit at its origin, in order to provide the protection necessary where, for example, cables are not buried more than 50mm deep under plaster (most cases I imagine) This suggests that the options are RCD (or RCBO) protection of the individual circuit or replacement of the CU inits entirety, thus bringing all circuits into the scope of 17th edition. I take it that RCD sockets will not provide the protection required, as per TTC's response.

 

[flameport]

An alteration to an existing circuit brings all of that circuit within the remit of the 17th edition

No, only the added/altered part of it.

However the easiest option is to add an RCD to the whole circuit. Either as an RCBO in the consumer unit, or a separate RCD in an enclosure.

Sensible options are:
1. Surface wiring and RCD socket outlets
2. Concealed wiring, normal sockets, add an RCD to the whole circuit

Other options:
3. Concealed wiring, normal sockets, add an RCD to the extended bit only, which will result in an RCD in a box stuck on your new lounge wall. If it's a ring circuit, then the RCD could only supply one socket as a spur, so for 2 spurs, 2x RCDs would be needed, and if extending the ring then there is no way to add an RCD to part of the circuit.
4. Fit an RCD fused spur and connect the new sockets to it. However this means the FCU would be in the lounge right next to an existing socket, plus all of the new sockets would be limited to 13A total, which is probably not what you want.
5. A new CU could be fitted with the required RCD in it, however this will obviously cost far more.

 

[echoes]

An alteration to an existing circuit brings all of that circuit within the remit of the 17th edition. Is that correct?

No, just the alteration must be 17th edition compliant.

Therefore, it will be necessary to protect that circuit at its origin, in order to provide the protection necessary where, for example, cables are not buried more than 50mm deep under plaster (most cases I imagine)

Not neccessary, but desireable, and could be easier.

This suggests that the options are RCD (or RCBO) protection of the individual circuit or replacement of the CU inits entirety, thus bringing all circuits into the scope of 17th edition.

Not quite, although if you do get a new CU, you do not necessarily have to get rid of the old one. Changing a CU and keeping the existing wiring in place would not neccessarily mean that all aspects of that circuit are to 17th. Protection and overload would be (ie. the scope of the work), but you might still have inaccessible junction boxes, for example which were permitted at the time of installation but may not be permitted to be installed now.

I take it that RCD sockets will not provide the protection required, as per TTC's response.

They will not provide the protection required for cabled buried in plaster < 50 mm without protection. So they could be used, but only with unsightly surface wiring/mini trunking.

EDIT: I vote for flameport's option 2, now I've seen it.

 

[spongsdad]

Thanks for all the helpful replies. I think that replacement of the CU to give some spare ways and to provide residual current protection on all circuits might be the most sensible-and future proof option. One last point; referring to my original post-what documentation should my son expect to receive from his contractor on completion of the work, particularlly if he goes down the route of a new CU?

 

[Paul_C]

Just be clear that when talking about the "requirement" to provide RCD protection on sockets & cables as outlined above, this is to achieve compliance with the current edition of BS7671. But as installing to BS7671 is not mandatory, there is no legal requirement to do it.

If none of the existing cables are RCD protected, adding a few yards more for a couple of extra sockets without going to the trouble of adding such protection is hardly a matter of great significance.

 

[Spark123]

As the work is being scoped by an electrical contractor then he will probably want his work to comply with the current regs owing to his head being on the chopping board and could be subject to inspection by a competent person scheme.
I can understand him being between a rock and a hard place!

 

[Paul_C]

As I just read in a comment in another thread, there's definitely a problem with those who can't see beyond BS7671. Although I do have to wonder what they think the deviations section on the certificate is there for!

 

[Spark123]

I can see beyond BS7671 as I also work to other standards for fixed installations, however remembering we haven't actually seen the job and the electrical contractor has I would side with him.
At the end of the day, I wouldn't want to be classed as a cowboy for installing something that could warrant an unsatifactory result on a PIR.

 

[spongsdad]

As I just read in a comment in another thread, there's definitely a problem with those who can't see beyond BS7671. Although I do have to wonder what they think the deviations section on the certificate is there for!

What I was trying to establish was whether there was a necessity for RCD protection as opposed to a desirability
I thought that I had understood from the responses that RCD protection was essential. Now I am not so sure. (Not that it will change my recommendation to my son to add RCD protection.)

 

[ajrobb]

I thought that adding sockets and lights to existing circuits but not in kitchens and bathrooms was an explicit DIY exemption under Part P so that Local Authority Building Control do NOT need to be notified. If that is correct, there would be no point making the exemptions if the CU has to be altered and notified. That said, upgrading the CU to modern regulations adds considerable extra protection (RCDs, bigger meter tails and bonding conductors).

 

[sparkiemike]

As I just read in a comment in another thread, there's definitely a problem with those who can't see beyond BS7671. Although I do have to wonder what they think the deviations section on the certificate is there for!

By "deviations" do you mean "Details of departures from BS7671 (Regulations 120.3 and 120.4)"? Have you read 120.3 and 120.4?

120.3 This Standard sets out technical requirements intended to ensure that electrical installations conform to the fundamental principles of Chapter 13, as follows:
Part 3 Assessment of general characteristics
Part 4 Protection for safety
Part 5 Selection and erection of equipment
Part 6 Inspection and testing
Part 7 Special installations or locations.
Any intended departure from these Parts requires special consideration by the designer of the installation and shall be noted on the Electrical Installation Certificate specified in Part 6. The resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations.
120.4 New materials and inventions
Where the use of a new material or invention leads to departures from the Regulations, the resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations. Such use is to be noted on the Electrical Installation Certificate specified in Part 6.

If you are going to have a departure from the regs you need to be able to demonstrate that your design "shall be not less than that obtained by compliance with the Regulations", which is not the same as saying you pick and choose which regs you want to comply with!