Workshop Main Feed

I've just had a new workshop built and I would like to get a 100A supply into it but I'd appreciate some advice on the best way to achieve this.

All the cable run is internal to the house and will be about 10m total. The majority of the the cable run will be under an uninsulated suspended wooden floor (free air would probably be about the closest reference method). There will be a short section in trunking where it passes through a wall and then about 3m clipped to the wall up to the consumer unit.

I initially thought 25mm^2 3 core armoured but I think that may be overkill for this as it's not exposed to the elements or running anywhere that it might get damaged. The alternative I've been looking at is 25mm^2 double insulated meter tails plus a suitably large earth (at least 16mm^2).

At the supply end I have 3-phase coming in. I have the house on one phase and I was planning on putting the workshop on a different phase. What's the best way to split the neutral? I was thinking a 100A service connector block. I think this would be easier to wire with the meter tails so another benefit of that option.

Are there any other options? Does meter tails and a service connector block sound like a good solution?

Cheers.

Sounds like you need to employ an electrician, who can advise you!

In no way is this a DIY job

PrenticeBoyofDerry said:

Sounds like you need to employ an electrician, who can advise you!

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You've forgotten your switch fuse...

You don't say what kind of workshop this is, but if it really needs 100A, then the obvious choice would be to take all 3 phases to it, which also provides the opportunity to have 3 phase equipment in there.

I have a 125A rated 3P+N switch at the supply which currently feeds just the house CU.

The workshop (wood and metal work) won't require anything like 100A but I have it available, if I can get it in there so much the better. In reality I'd estimate absolute maximum draw to be 40A but that would be very unusual, typical maximum would be more like 20A for short durations (a few minutes). I don't have any 3 phase equipment and I don't see myself getting any, if I do find something that requires 3 phase I'd most likely run it from a phase converter.

I'd be happy with 80A (or perhaps even 60A) into the workshop. Looking at the on-site guide it would seem 16mm^2 T&E cable clipped direct should be good for 85A. It would mean finding a CU that has an 80A main switch available but I'm sure a little digging will turn a few up.

Really, PLEASE get an electrician. You are not one, and not even close to being able to carry out this work.

What do you mean by

wobblycogs said:

It would mean finding a CU that has an 80A main switch

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How would you expect that to have ANY effect on the current?

wobblycogs said:

It would mean finding a CU that has an 80A main switch available but I'm sure a little digging will turn a few up.

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There is no problem with using a switch which is rated higher than the maximum load.

Some one will need to issue either a compliance or completion certificate for this work. The latter will likely be the more expensive option so really you need a scheme member electrician.

wobblycogs said:

Looking at the on-site guide it would seem 16mm^2 T&E cable clipped direct should be good for 85A.

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Just dip my spoon in a little!
But you have not accounted for the section of trunking you intend to use as containment, which would reduce the current carrying capacity of the cable.
It is evident you do not require a 100A or 80A load demand or supply, what you do require is an electrician on site to advise you. Whether that is just to confirm rating, cable sizing, routing and installation techniques I don't know? What I can gather is that this project is beyond your scope without experienced help! (no disrespect, you can still carry out the donkey work)

Worry not, I now have an electrician lined up to do some calculations and specify cabling, equipment, routing, etc. Running a new ring in is one thing this, as you say, requires someone with some experience.