Add RCD to Shed supply and update

northbank_dom · 2 Sep 2021

I currently have a 13A fused spur that supplies power to my shed. This would have been done at a time that predates current standards, and as I've now replaced the shed (but kept the existing supply), I'd like to add some sockets and modernise it where I can without having to run a new supply.

Currently it's as follows:

13A fused spur -> conduit to shed -> junction box ->
- 5a switched spur -> light
- double socket

I'd like to add RCD protection in place of the standard 13a fused spur, add a DP isolator and add additional sockets, similar to option 2 in the following, but with additional sockets.

https://electrical.theiet.org/media...tdoors-a-supply-to-a-detached-outbuilding.pdf

My understanding is that it's not notifiable because the existing supply predates current standards, but I obviously want it to be safe, so I'll likely complete the cabling in the shed from the isolator switch onwards, then get a pro to verify it before making it live.

Does the diagram attached seem sensible?

flameport · 2 Sep 2021

Does the consumer unit in the house have RCD protection in it?

northbank_dom · 2 Sep 2021

flameport said:
Does the consumer unit in the house have RCD protection in it?

Just checked and no it does not appear to. There's an RCD for a macerator on the same ring though.

ericmark · 3 Sep 2021

Using a RCD FCU seems to be simple way to add RCD protection, technically it does not comply as the BS EN numbers for a RCD FCU are not the same as stand alone units, and BS 7671 states what BS EN number should be used, but that is being rather pedantic, and I would fit a RCD FCU without any worry. It must be an improvement.

The IET wiring matters is dated 2005 so we have had two editions of BS 7671 since then, again technically it is design date which matters, and by adding a RCD you are changing the design, so it should comply with current regulations, and you would need to write out a new installation certificate so not so sure if considered as a new circuit, using the minor works form would likely be better, as then not seen as new circuit, but unless rented property would anyone care or bother checking?

There is a huge difference when an electrician does work which is registered with his scheme provider and LABC and so many of his jobs will be inspected by scheme provider so some one is checking their work so it must be A1, with DIY it is more down to common sense, unless rented where you know it will have regular EICR done.

northbank_dom · 3 Sep 2021

It's not rented, but of course I want to be safe. I don't seem to have much luck getting competent people in or being able to find them. I've found someone who seems sensible now. Just wanted to make sure that my proposed plan is sensible and safe, then I can get the conduit and sockets run for him to finally cable and test.

yorkspark · 3 Sep 2021

ericmark said:
Using a RCD FCU seems to be simple way to add RCD protection, technically it does not comply as the BS EN numbers for a RCD FCU are not the same as stand alone units, and BS 7671 states what BS EN number should be used, but that is being rather pedantic, and I would fit a RCD FCU without any worry. It must be an improvement.

Except bs7288 explicitly says that rcd spurs cannot be fitted to a circuit which does not already have additional protection already fitted, ie they cannot be fitted unless the circuit is already rcd/rcbo protected.
it isn't an improvement fitting an rcd spur standalone as they do not offer additional protection or safe isolation and they are an obsolete product, hence there withdrawal from bs7671 in jan 2019 and fitting them standalone is a non compliance.

northbank_dom · 3 Sep 2021

In which case it sounds more sensible if I forget the RCD, leave in place as is and at least add an isolator switch at the shed end. I actually wanted an exterior socket. Is it possible to add this without an RCD? It would be via 20mm conduit, directly into the back of an IP66 rated double socket. Attached a rough diagram.

flameport · 3 Sep 2021

All new socket outlets require RCD protection. So do lighting circuits in domestic premises.
Sockets that can be used for items outside have required RCD protection for decades.

The only compliant ways to add RCD protection is to add it in the consumer unit which almost certainly means replacing it, or to add a separate RCD next to it for the socket circuit only.

northbank_dom said:
My understanding is that it's not notifiable because the existing supply predates current standards,

What's notifiable is determined by the list of things that are, which in England is new consumer units, new circuits or things within the zones of a bathroom. How old it is doesn't change anything.

northbank_dom · 3 Sep 2021

flameport said:
All new socket outlets require RCD protection. So do lighting circuits in domestic premises.
Sockets that can be used for items outside have required RCD protection for decades.

The only compliant ways to add RCD protection is to add it in the consumer unit which almost certainly means replacing it, or to add a separate RCD next to it for the socket circuit only.

So If I can’t add an RCD to the shed because the main board isn’t RCD protected, I can’t add an external socket? Or are you saying now that I can add an RCD in the shed to protect the external socket only (that’s the only new socket), and that doesn’t require an RCD protected main board?

AndyPRK · 3 Sep 2021

No

It’s wise to spend your money on having the CU upgraded. This will have RCD protection

northbank_dom · 3 Sep 2021

Ok. So a new CU would add RCD protection. Does that still mean a secondary RCD is required for the shed mains radial so that I can run an external socket? Or would that now mean the 13a fused spur from the house is sufficient?

northbank_dom · 3 Sep 2021

flameport said:
What's notifiable is determined by the list of things that are, which in England is new consumer units, new circuits or things within the zones of a bathroom. How old it is doesn't change anything.

Just going back to the initial problem. This is not a new circuit, this is an existing installation where the intention was to replace the old wiring and sockets like for like, and if possible, add RCD protection and an external socket.

By the sounds of it I think the easiest and most compliant option is going to be to just replace the original sockets and wiring as is, and not add any RCD or external sockets.

AndyPRK · 3 Sep 2021

northbank_dom said:
Ok. So a new CU would add RCD protection. Does that still mean a secondary RCD is required for the shed mains radial so that I can run an external socket? Or would that now mean the 13a fused spur from the house is sufficient?

Once you had a new CU with RCD protection. (or RCBO) you wouldn't require any other RCDs

yorkspark · 3 Sep 2021

northbank_dom said:
Just going back to the initial problem. This is not a new circuit, this is an existing installation where the intention was to replace the old wiring and sockets like for like, and if possible, add RCD protection and an external socket.

If you removed all the original wiring and replaced with new, then of course its a new circuit as there wouldn't of been a circuit there, as you removed it!!

northbank_dom said:
By the sounds of it I think the easiest and most compliant option is going to be to just replace the original sockets and wiring as is, and not add any RCD or external sockets.

Once again, replacing the wiring makes it a new circuit so will require rcd protection. Just bite the bullet and either get an rcbo fitted in the cu, or an enclosure with a 61008 rcd fitted adjacent the cu and do the job properly.

EFLImpudence · 3 Sep 2021

yorkspark said:
If you removed all the original wiring and replaced with new, then of course its a new circuit as there wouldn't of been a circuit there, as you removed it!!

Surely that is, as you have said, merely a replacement.

Replacements have never been notifiable - until in England in 2013 when they decided, for some reason, that replacing a consumer unit is notifiable; presumably meaning that fitting a new one where there was not one before is not notifiable.

Once again, replacing the wiring makes it a new circuit

Nope.

so will require rcd protection.

Yes, if it is new concealed cable.

Just bite the bullet and either get an rcbo fitted in the cu, or an enclosure with a 61008 rcd fitted adjacent the cu and do the job properly.

Surely he could fit either in the garage.

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Add RCD to Shed supply and update

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