Garage Consumer Unit

[DIYdar]

Hi all,

I am currently in the latter stages of completing a major garden overhaul part of which includes a new outbuilding at the end of the garden.

The main feed to the outbuilding is 6.0mm 3 core swa which I am planning to run into a consumer unit to power 1 x ring main, 1 x lighting circuit and 4 x LV water features.

Although i have been in regular contact with my electrician (im getting the bits he's doing the connections) i have a couple of questions which i cannot ask him as he's off on holiday now.

My questions are:

1/ He recommended a 4/6 way RCD consumer unit (to cover future expansion). Can anyone recommended current good makes or anything to look out for?

2/ The cable runs back to the main CU in the house and i was hoping to use a 32a mcb that formerly powered an electric shower but it is on the RCD side of the board and there is no space on the non rcd side. Is this ok?

This is as much for my interest purposes as anything else.

Cheers

 

[Taylortwocities]

You need to ask your electrician all of these questions.

If the spare MCB is on the RCD side of the board then you do not need an RCD consumer unit in the outbuilding.

Personally I would prefer the outbuilding feed to be on the non-RCD side of the board. That would mean that a fault on the outbuilding circuit would not trip the house's RCD (thus losing power to your fridge/freezer while you are away for a weekend).

It may be possible for the spare MCB to be moved to the non RCD side but only your electrician will be able to determine if this is possible.

Choice of consumer unit is usually done by the electrician as he will have his own preferred maker(s) that he carries spares for. All of them meet the relavent standards but some are a PITA to install.

Some of them will allow the SWA to be glanded directly to the CU, some require an additional termination box. This depends on the method, how the cable is presented and also on the supply type. You are not allowed to use metal boxes of the supply type is TT, for instance, unless certain other safety precautions are provided.

 

[ban-all-sheds]

I wonder why your electrician chose a ring for the sockets in the shed?

Anyway - as TTC said - if you can't reach him because he's on holiday you'll have to wait.

When this is all done you'll be wanting him to certify that he did it all -design, installation and testing, and that it all complies with the Wiring Regulations, and you'll be wanting him to tell the council that it all complies with the Building Regulations.

You have to let him be 100% in charge.

 

[holmslaw]

..

 

[Taylortwocities]

I thought that too, BAS, why a ring.

A radial protected at 20A is the way otherwise a standard ring final with 32 amp breaker in the shed will not discriminate with the 32A CPD in the house.

Or is there something that you spotted, jungle bunny?

 

[JohnW2]

I thought that too, BAS, why a ring.
A radial protected at 20A is the way otherwise a standard ring final with 32 amp breaker in the shed will not discriminate with the 32A CPD in the house.

Although not necessarily a reason, per se, for having a ring, maybe (s)he needs more than 20A (we've been told nothing about demand)?

Kind REgards, John

 

[ricicle]

There is no guarantee that any of the MCBs, whatever their In, will discriminate with the 32A MCB at the house. Feeding an MCB board from an MCB is poor practice.

 

[JohnW2]

There is no guarantee that any of the MCBs, whatever their In, will discriminate with the 32A MCB at the house. Feeding an MCB board from an MCB is poor practice.

Indeed. Presumably there would be no need to have any MCBs in the garage if it was supplied by an MCB in the house and the lighting and water features circuits came off as FCUs. Such an approach would obvioulsy favour a radial power circuit, to avoid having to take two cables back to the MCB in the house.

Whether a lack of discrimination would really be that much of an 'inconvenience' if both he devices are dedicated to essentially the same circuit is another matter.

Kind Regards, John.

 

[DIYdar]

Thanks everyone for all your replies, interesting reading.
I think I may have just assumed that the sockets will be on a ring, the only planned loads I will be putting on the sockets are a tumble dryer (definitely now) and a fridge (maybe,later).

Is the 20a radial the way to go then? It would be good to clarify this with him when he gets back.

With regard to not running an mcb cu from an existing mcb, what would be the alternative way of doing things?

Sorry for all the questions but this stuff fascinates me and I'd just like to understand a bit more about it!

TIA

 

[Taylortwocities]

With regard to not running an mcb cu from an existing mcb, what would be the alternative way of doing things?

Best option might be a switched fuse in the house with an RCD protected consumer unit in the shed with MCBs.

If only these electricians would not keep going on holiday....

 

[DIYdar]

I see! All makes perfect sense, although I think I'll leave it for him to worry about rather than dedicate too much thinking time to it myself!

Nice to understand what's going on though.

As for electricians and holidays, must be all the money they're making out of people like me...

Thanks again for your help