Running a circuit between two domestic garages.

[Wickhammersley]

I've recently purchased an additional garage in a row of garages; it's a couple of garages away from my existing garage.

The existing garage has an electricity feed from my house; about 10m away. The feed is sourced from the consumer unit in the main house and sits behind an RCD protected BusBar and subsequently a B32 MCB.

The existing cable feeding from this B32 MCB and to the existing garage appears to be 16mm2 armoured cable.

The existing garage has a small two gang consumer unit with two plug in MCBs; 16A feeding a twin socket and 6A feeding an internal and external light.

The new garage has a couple of other garages in-between. The owners of these two garages have agreed that I may run conduit through the lofts of their garages to my new garage.

I wanted to educate myself before engaging with an electrician who will undertake the work; I like to know a little about what I'm asking / expecting.

I'd envisaged that we'd run a 10mm2 cable between the two garages adding a third consumer unit in the new garage; to service a couple of sockets and lights (the sockets bearing light usage).

Q1. To archive this would we likely replace the consumer unit in the old garage with a three / four gang consumer unit and protect the run to the new garage with a 16A MCB in the old garage and terminate with another consumer unit in the new garage? I'm assuming it would be bad practice to simply run a 2.5mm2 ring main and 1.5mm2 lighting circuit between the two garages from the existing old garage MCBs.

Q2. If replacing the consumer unit in the old garage and adding a new consumer unit in the new garage is the correct approach, is it bad / wrong to use consumer units in both the old and new garages that whose circuits are protected by an RCD? i.e. to use RCDs in series.

I'm sorry if these two questions appear daft; I'm just attempting to knowledge up before talking with an electrician.

I'd really appreciate any guidance you might have to offer.

 

[flameport]

You could do what you suggest, but 10mm is grossly oversized, and you do not need a CU in the second garage (or in the first one), and 16mm for the supply is also ridiculously large for a 32A circuit.

With what is there, the simplest option will be to extend the lights and sockets from the existing garage CU using 2.5mm and 1.0mm cable. There is no ring, it's a 16A radial.

 

[EFLImpudence]

I wanted to educate myself before engaging with an electrician who will undertake the work; I like to know a little about what I'm asking / expecting.

Someone may post some reading material links for you.

I'm sorry if these two questions appear daft; I'm just attempting to knowledge up before talking with an electrician.

They aren't daft but take too much explaining to answer.
More verbose posters may wish to type pages.

Why not have a chat with an electrician face to face and he can do it?

 

[AndyPRK]

Certainly johns suggestion was my first thought. Or maybe use singles in the conduit.

However at some point you may wish to isolate the other garage, so a 3 way cu does not seam such a bad idea, with 1 cable going to the new garage.

Use an fcu with a 3a fuse as a light switch in the new garage.

Will you have a new external light on that garage ?

If your 2 way cu were to become spare you could move your 2 way cu into your new garage but rather pointless.

 

[Wickhammersley]

Okay. Thank you each for your answers.

To address questions and comments by return;

- The 16mm2 cable from the house to the first garage is pre-existing. It was installed by the builders.
- I'd feared that running either a 13A radial or ring and a lighting circuit from the Consumer Unit in the first garage to second garage might be deemed bad practice as it effectively passes over two other garages. I'd suggested to the neighbours that it would be a single 20mm conduit that ran through their loft spaces. Does 2x2.5mm2 and 1x1.5mm2 cables in a 20mm conduit sound too tight? I guess I could use 25mm conduit instead and they probably wouldn't notice.
- Might it be an option to run a single cable from the 16A MCB in the first garage to a small Consumer Unit in the second from where we could run both a 16A MCB to a couple of sockets and a 6A MCB to the internal / external lights? And, if so, should I be avoid using a Consumer unit in the new garage that includes a RCD.

I guess I just want to ensure we go for the best and most future proof solution; the part costs for this are minimal it'll just be a few hours labour so I'm not that concerned about costs.

 

[EFLImpudence]

You are now getting confused and giving the impression that there will be no electrician involved.

 

[Wickhammersley]

You are now getting confused and giving the impression that there will be no electrician involved.

Sorry EFLImpudence, but not at all; I just want to do my homework before the electrician arrives. I like to be in the position where I understand what I'm being told / advised by a professional. I'd like to be part of, or at least understand, the decision making process; but electrical stuff is (as you can tell from my failed understanding above) way beyond my ability.

My concern was that I might have misled the neighbours as to what would be passing through their garage lofts; I wondered if I'd been too simplistic.

But thanks, and fear not; I'm not about to tackle household wiring with a pair of shears; opening the flap on the consumer unit is as far as I dare!

 

[EFLImpudence]

Then all you need to do with the present set-up is do as flameport said.

 

[Wickhammersley]

Thank you to each. Your contributions are greatly appreciated. I feel as though I'm in a much better position to speak with the electrician and to understand what he's saying. The theory is he'll pop around on Tuesday evening to take a look; hopefully, from there, we can get it sorted pretty quickly.

Thanks once again and apologies if I've offended.

 

[AndyPRK]

Yes 2x 2.5mm does sound too tight for conduit. But you don't need a ring.

Conduit is good should you need to replace cable in the future and prevents damage if people use their lofts.

 

[EFLImpudence]

Not offended but there really is more to it.

Your present set up is not what would have been advised if you were asking to install that.
However, as it is already like that, there is no point doing anything other than adding another socket and light as if it were in the same room.

 

[bernardgreen]

You need to get a written statement from the owners of the garages that they have granted you a wayleave to run electrical cables through their property. If there was a change of ownership then without you having a written permission for a wayleave the new owner could demand you cease the trespass on their property.

Use a conduit that is large enough to pull the cables through without having to go into the other garages once the conduit is installed. Mark the conduit along its length with clear labels that say that it contains electrical cables.

 

[Wickhammersley]

You need to get a written statement from the owners of the garages that they have granted you a wayleave to run electrical cables through their property. If there was a change of ownership then without you having a written permission for a wayleave the new owner could demand you cease the trespass on their property.

Use a conduit that is large enough to pull the cables through without having to go into the other garages once the conduit is installed. Mark the conduit along its length with clear labels that say that it contains electrical cables.

Thanks BernardGreen; that's a really good point. I guess there's always likely to be an element of risk here but your suggestion is a good one. I'll ask them.

A larger conduit sounds good too; I'll mention it. Sounds like good futureproofing.

 

[ban-all-sheds]

I wanted to educate myself before engaging with an electrician who will undertake the work; I like to know a little about what I'm asking / expecting.

You're asking her to run cable(s) from one garage to another to supply sockets and lights in the 2nd garage. I struggle to see what more there is to ask, given that she has to sign an EIC to say that she did the design, not you.

I'd envisaged that we'd run a 10mm2 cable between the two garages adding a third consumer unit in the new garage; to service a couple of sockets and lights (the sockets bearing light usage).

You may have done, but...

Q1. To archive this would we likely replace the consumer unit in the old garage with a three / four gang consumer unit and protect the run to the new garage with a 16A MCB in the old garage and terminate with another consumer unit in the new garage?

What does your electrician, who will be signing a declaration to say she did the design, think?

I'm assuming it would be bad practice to simply run a 2.5mm2 ring main and 1.5mm2 lighting circuit between the two garages from the existing old garage MCBs.

Why?

Q2. If replacing the consumer unit in the old garage and adding a new consumer unit in the new garage is the correct approach, is it bad / wrong to use consumer units in both the old and new garages that whose circuits are protected by an RCD? i.e. to use RCDs in series.

What does your electrician, who will be signing a declaration to say she did the design, think?

I'd really appreciate any guidance you might have to offer.

I'd advise spending your spare time studying structural engineering, as there is much more to learn there, and it's harder, so if you ever needed to engage one for a building project you'd face a major delay while you knowledged up enough to be able to talk to one, since you seem to have trust issues.

 

[Wickhammersley]

Thank you Ban-All-Shed but goodness, how the locals seem to have turned.
I asked because I am interested in gaining knowledge; I will never, nor intend to, speak to the electrician on equal terms but I'm interested in lessening my knowledge gap.
I will ask him when he pops in on Tuesday and I'll certainly trust and follow his recommendations [and I don't understand the italicised gender either].
And trust issues; me thinks you read too much between the lines.
I work in IT and I applaud those who try to gain some knowledge before approaching; I respect the effort. I'm merely practicing what I...
I'm sorry if I have disturbed; I meant no ill. But thank you each for your helpful contributions.