Garden office/Shed Electrics

[ashtraywasp]

Which law would that be?

I saw it on a video about the UK law on modifying existing CUs, quoting Document P. Unsure of how true it is.

Some less feasible and/or more expensive than others.




Yes, if there's an unprotected section with capacity in the house CU, you don't mind losing all power to the outbuilding if there's a fault, and you don't mind schlepping back to the house to reset the RCD if it trips.




Yes, because most people do mind losing all power to the outbuilding if there's a fault, and do mind schlepping back to the house to reset the RCD if it trips.

I'm unsure if there's an unprotected section in the house already, there are gaps between subsections of the main CU, so there mught be space to put an MCB or RCD in there.

The building is 1m away from the back entrance to the house so it's not terrible to have to go in in case of a fault, but I guess ideally I would like to just go to the shed side of the garden office to deal with it, it's more that the cost of RCBOs per subcircuit is a fair bit more than running MCBs downstream from one RCBO, and in that case as the subcircuits each have an RCBO, what connects the SWA cable to the main CU? That is what I'm more confused about.

 

[endecotp]

as the subcircuits each have an RCBO, what connects the SWA cable to the main CU?

An MCB.

 

[ashtraywasp]

An MCB.

And am I allowed to add all this myself and then get an electrician to certify it?

I understand the difference and advantages between this setup and having one RCBO in the main CU in the house connected to the SWA cable with only MCBs per subcircuit in the sub CU, but as the house is currently using the latter setup, and the garden office won't be used all day or with all appliances all on at the same time, is it ok to do it like the latter?

 

[ericmark]

There are three ways to do notifiable work.
1) Use a scheme member electrician.
2) Use the LABC in Wales where I live, it costs £100 plus vat, plus the cost of an electrician to inspect and test if the LABC inspector does not do it himself, unless you can convince them you can do your own inspection and testing, which is unlikely, and they need informing before you start.
3) Use a scheme member electrician who has the extra inspection and testing from his scheme provider in England only, not permitted in Wales, and very few have this extra to their scheme membership, so in real terms, you're unlikely to find anyone to do this, and again you have to get them on board before you start.

The electrician has to sign that he was controlling all work done, so can't do it after the event.

Likely it will be cheaper to get an electrician to put the supply in, even if you add to it latter.

In England, you're not allowed to add a circuit, or work in the bathroom. In Wales outside and kitchens are also special locations. (Old English rules were never changed).

But I see nothing to stop you making changes, the problem is really how pedantic the electrician you find is. Type AC RCDs are no longer used, and all the ones you show are type AC, so having a Metal fused connection unit (FCU) with a 13 amp fuse feed the shed, will be very much cheaper to having a 32 amp supply.

In England, you could fit a FCU yourself, and supply the shed, without really breaking any rules, but you can't really install a 32 amp supply yourself.

So a heat pump tumble drier and a small oil filled radiator maybe you could DIY, but you said washing machine as well.

You could ignore the rules, which for an electrician working on his own house is not so bad, as he knows if tested they will pass, so unlikely anyone will find out, as no one will likely get hurt. But anyone who goes to hospitial after an electric shock, will have the details passed on, so likely the HSE will come and have a look. So really you do need to be sure it is all OK, even if not legal.

As I said before, find how much it will cost to have an electrician do the work, if you need to pay £200 to make it legal using the LABC route, it may work out cheaper not to DIY.

 

[ashtraywasp]

Ah right, thanks for all the info.

We already have an FCU on the bedroom going to the outside, but yeah not gonna be enough with all my PC and equipment plus dryer and heater, even if we don't put the washing machine there.

I want the office to be insured so I will need to get it certified, I'm going to contact some local electricians and see what they quote, maybe can do the internal wiring ourselves and they can just inspect before any insulation or plywood covers it.

 

[Murdochcat]

Ah right, thanks for all the info.

We already have an FCU on the bedroom going to the outside, but yeah not gonna be enough with all my PC and equipment plus dryer and heater, even if we don't put the washing machine there.

I want the office to be insured so I will need to get it certified, I'm going to contact some local electricians and see what they quote, maybe can do the internal wiring ourselves and they can just inspect before any insulation or plywood covers it.

That is an excellent plan but don't start telling competent sparks how to do their job or they might just walk away.

 

[ashtraywasp]

That is an excellent plan but don't start telling competent sparks how to do their job or they might just walk away.

I never said I knew more than them, just that from looking at information online I found several ways to do things and needed input on what works best. Just wanted to do it the correct way and save money by doing what we can ourselves.

 

[Murdochcat]

I never said I knew more than them, just that from looking at information online I found several ways to do things and needed input on what works best. Just wanted to do it the correct way and save money by doing what we can ourselves.

I didn't say you would .................... and as for online information there is always guidance that is quite frankly wrong .........

 

[ashtraywasp]

Yeah that's true, I'll have a read through Document P and see what we can do ourselves and can't.

 

[morqthana]

I saw it on a video about the UK law on modifying existing CUs, quoting Document P. Unsure of how true it is.

Completely un.

I'm unsure if there's an unprotected section in the house already,

Should be obvious. Any ways not downstream of an RCD?

there are gaps between subsections of the main CU, so there mught be space to put an MCB or RCD in there.

Are any of these subsections not downstream of an RCD?

The building is 1m away from the back entrance to the house so it's not terrible to have to go in in case of a fault, but I guess ideally I would like to just go to the shed side of the garden office to deal with it, it's more that the cost of RCBOs per subcircuit is a fair bit more than running MCBs downstream from one RCBO,

Designing with the primary aim of making it as cheap as possible to save a few tens of pounds is a good way to end up with a carp design.

what connects the SWA cable to the main CU?

A BW gland.

And am I allowed to add all this myself and then get an electrician to certify it?

Depends on what you mean by "certify", but I'll hazard a guess at "no".

I want the office to be insured so I will need to get it certified,

Do you mean you need a Building Regulations certificate?

I'm going to contact some local electricians and see what they quote, maybe can do the internal wiring ourselves and they can just inspect before any insulation or plywood covers it.

Good luck.

I never said I knew more than them, just that from looking at information online I found several ways to do things and needed input on what works best.

My preference would be to keep the outbuilding off the house CU entirely.

 

[ashtraywasp]

Should be obvious. Any ways not downstream of an RCD?

There are two MCBs marked as Spare separate to any RCDs but I haven't opened the CU yet to make sure.

Designing with the primary aim of making it as cheap as possible to save a few tens of pounds is a good way to end up with a carp design.

Yeah the aim is to find a balance.

A BW gland.

I meant as in what module, not how to get it in the box.

Depends on what you mean by "certify", but I'll hazard a guess at "no".

I mean getting it approved by an electrician so I can insure the building and comply with the law.

Do you mean you need a Building Regulations certificate?

I'm not sure, whichever is a requirement after doing this sort of electrical work. I haven't done it before and I'm not from the UK so I'm unsure what is required.

My preference would be to keep the outbuilding off the house CU entirely.

Mine too but with the power requirements it seems impossible.


I also need to know if I can use 2.5mm T&E cable for the interior wiring as it will most likely be surrounded by glass wool insulation, or at least have it on one side with the other being the wooden joists or the membrane covering the cold side of the frame. I guess I might need 4mm for the outlets if I want to run 32A, as I have read if you surround it with insulation the capacity needs to be halved.

 

[Murdochcat]

I also need to know if I can use 2.5mm T&E cable for the interior wiring as it will most likely be surrounded by glass wool insulation, or at least have it on one side with the other being the wooden joists or the membrane covering the cold side of the frame. I guess I might need 4mm for the outlets if I want to run 32A, as I have read if you surround it with insulation the capacity needs to be halved.

So find a local spark ................... one who will allow you to do some of the work and is willing to test and certify the new installation