[Closed] Domestic Electrics

Firstly, how is the 4mm incoming cable fed? Consumer unit in the house?

What consumer unit have you bought for the garage end?

Isn't 4mm incoming a bit small?  Anyway, recently did a CU but used RCBO's, proper easy and very tidy.

I'd go size upon tails.

If I read this right you have fed a 2 way consumer unit in the garage with a 4mm back to the main service and now want to connect this to an RCD with an outgoing mob to protect the garage circuit.

So you will need to split the incoming tails through a Henley block (100A DP terminal block) then take new tails from this to the existing consumer unit 25mm? and to the RCD / Mcb unit. As the garage feed is only 4mm I would suggest fitting no larger than a 30A mcb for the garage and use 6 or 10mm tails to the new RCD. Or get a sparks.

>So you will need to split the incoming tails through a Henley block (100A DP terminal block) then take new tails from this to the existing consumer unit 25mm? and to the RCD / Mcb unit. As the garage feed is only 4mm I would suggest fitting no larger than a 30A mcb for the garage and use 6 or 10mm tails to the new RCD. Or get a sparks.

Basically what I did, although I used 10mm for the workshop feed...

House end

[url= https://farm8.staticflickr.com/7382/16338950476_84cd619b1f_z.jp g" target="_blank">https://farm8.staticflickr.com/7382/16338950476_84cd619b1f_z.jp g"/> [/img][/url][url= https://flic.kr/p/qTPoJG ]Consumer Units[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

Middle bit

25mm steel conduit running along cant rail

[url= https://farm9.staticflickr.com/8229/8601173230_750c150702_z.jp g" target="_blank">https://farm9.staticflickr.com/8229/8601173230_750c150702_z.jp g"/> [/img][/url][url= https://flic.kr/p/e74g9b ]Kitchen end[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

Workshop end

[url= https://farm8.staticflickr.com/7563/15929349686_b57e5a9753_z.jp g" target="_blank">https://farm8.staticflickr.com/7563/15929349686_b57e5a9753_z.jp g"/> [/img][/url][url= https://flic.kr/p/qgC5G7 ]Workshop Consumer Unit[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

Nice job Ben. Love a bit of conduit. Garage consumer unit needs dressing in though and it's a bit out of level😉

It's not clear to me quite what your set up is. Maybe a sketch will help.

My workshop consumer unit is fed from the house consumer unit. It's on a non RCD circuit. The SWA goes directly from that to the workshop consumer unit and into the local RCD. No need for extra tails. If you don't have a spare circuit in the main house box than you'll need to split it as above. If the SWA is 4mm then no need for anything bigger elsewhere but make sure you have the right overcurrent protection.

Just one thing to add. I've added a 40A cooker switch by the door to the workshop by the light switch. Then one ring of sockets goes through that. It means I can turn all those sockets off when I leave the workshop.

Incoming cable is 4mm, 3 core, SWA.  (Cable already in use with existing 2 fuse distribution box) From consumer unit in house. Already in position, and has been in use.

Incoming breaker is 100A DP. Breaker in garage consumer unit

RCB is 63A DP. RCB in garage consumer unit

Then feeding 3 x 6A and 2 x 16A MCB’s, only MCB's in garage consumer unit

Question is, what size cable tails from incomer to RCB? Tails from 100A MCB to 63A RCB. Next to each other in garage consumer unit. Length 100mm max.

4mm or 6mm.

I think 4mm.

Have got Hager MCB's, Consumer unit box will be Pro-Elec, empty. I will populate with the MCB's that I have here.

In that case anything 4mm or bigger will be fine current wise. They are normally bigger so just make sure they sit in the terminal ok. The current protection will be at the house. Just ensure that it is fed from the correct value MCB (probably around 30A but you should do the calcs)

" Garage consumer unit needs dressing in though "

Very tactful. 🙂

😉

On my list of projects as I need to rewire the garage, which for some reason is currently fed off the upstairs socket ring.... I was told for work in an out building you needed a part p sparky.

i already have a secondary 100a breaker set up for an old consumer unit in the back part of the house (which was rented out) so was planning on using that to feed the garage cu

i expect the draw from a workshop could be pretty high with mitre saws and the like.  What size cable should I use?

I plan to do the majority of the wiring and ask a sparky to come in, do the final connections and the safety checks

>Garage consumer unit needs dressing in though and it’s a bit out of level

Too much slack on the rails. Once you stick the cover on, it forces them all in line!

>I plan to do the majority of the wiring and ask a sparky to come in, do the final connections and the safety checks

Basically what I did. Alanl (of the STW parish) acted as consultant and Building Control had a sparky come out, test it and sign it all off.

The workshop was a new build (see Rate my bricky thread), so it was all part of that.

All electrical work needs to be done to part p. The issue is whether it is notifiable. You can get a spark in who can self certify or go through building control. Whether your job is notifiable depends on a few factors including where you are located, the rules are different in England, Scotland and Wales.

You can't just "have a go" then get someone in to sign it off. You need to either notify building control before you begin or get you spark involved at the design stage.

Mitre saw won't draw much but other equipment might. You need to work out the load. You can then work out the cable size and correct protection. How the cable is mounted and how long it is will also be a factor.

Respectfully I'll disagree.  As I have first hand experience of pulling the boards, running the cable and wiring up all the sockets, then getting the sparky in to check my work before it was energised, do the cu bit then check it it passes all the safety tests and issue the cert.  It was all uncovered for him to inspect

As as for design, sounds a bit grand, those sparks I have worked with all seem to operate of a bunch of standards for installations.

I don't doubt you'll find plenty of sparks happy to bend the rules a bit. As for "Design", it is a direct quote from the declaration that is signed to state the installation is in accordance with BS7671. I suspect those sparks that bend the rules are happy to lie on the declaration too. Personally I have no issue with cutting a few corners when it comes to DIY. The tricky bit is just knowing what corners to cut.