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"garage" consumer unit


mistymoo

Question

Hello.

I'm in the process of putting power to someone's shed. As they wanted sockets and a light (greedy! :^O ) I've put a small consumer unit in the shed with an RCD and 2 mcbs.

I've run the cables supplying the shed from a consumer unit that had a space on it in their main building. It was another small cons unit on which the other mcb is for the washing machine.

The building is on 3 phase supply but the half of the building that I'm working in is only one of the 3 phases as the building used to be split into 2 units but is now one. Its on a TN-S system. The small existing consumer unit (the one with the washing machine mcb on it) has no main switch before it (the incoming line is not able to be switched off) as I found out today (don't worry I was using my fused test leads!)

Now I need to test.

Can anyone tell me where I test from? And what I should test? Obvoiusly not the whole thing as I didn't build it but I do need to test my work in the shed. I also need to make sure the cable I put to the shed is ok.

Can I test from the "washing machine" cons unit and through my cons unit in the shed or will that upset the RCD on the cons unit in there?

Ze? Where do I test that from? (I know in theory but which bits do I actually test from?)

Help is required ASAP please as I would like to test tomorrow!

Thank you!

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18 answers to this question

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Thank you. That would be nice.

Bless your little cotton socks. O)

You clearly don't quite realise the implications......................

:o

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Ze should always be tested at service head. at second CU, you can test there as Zdb

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test. DNO will state limit for earthing system, and if something has gone wrong outside (failed joint etc), then it wont be noticed, possibly leaving property without an earth

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What about R1+R2? I can easily test these in the shed but as I put the cable from the main building to the shed I need to test this somehow, don't I?

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you need to test R1R2 on your submain between house and garage. and Zs at garage (which is also your Zdb). you then test R1R2 on what ever circuits you have in there, along with your Zs. treat garage DB as a normal house DB for all testing, just its supplied from another DB and not DNO.

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for R1R2 on submain, test as you would do on any other circuit. i.e instead of a cooker at the end, you have another DB instead

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I'm going to go with my second option... The other way around.

I figure if I pretend my new cons unit in the shed (or DB as andyc has called it) is a ceiling rose then I can test the submain (my new word of the day) for R1+R2 and insulation resistance as well.

Does this sound reasonable?

Then I'll test the circuits in the shed like it was a normal house.

Any ideas how I fill in the form to illustrate what I have done please?

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that will work for R1R2/IR etc. can be done at either end, more personal preference as to which end you use for what

for test sheets, fill in as normal, but you will have either:

1 schedule of tests (if you have only installed the subamain from existing, mark results from this on line 1 and mark that its the submain)

2 schedule of tests (if you have more circuits from db1 you need to mark, i.e if you installed a few circuits, you would list all of those, inc submain, then other test results would be for garage). you could use this option for above, if you didnt want to use line 1 as submain

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Thanks. I only added the one submain, the new DB in the shed, a lighting circuit off the new DB and 2 double sockets on a radial all in the shed.

You have been very helpful. More helpful than the irritating man on the Fluke helpline when I rang them today but that's another story.

Thanks! ;)

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Thanks. I only added the one submain, the new DB in the shed, a lighting circuit off the new DB and 2 double sockets on a radial all in the shed.

You have been very helpful. More helpful than the irritating man on the Fluke helpline when I rang them today but that's another story.

Thanks! ;)

Perhaps I should send my boys round.

The Godfather

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Perhaps I should send my boys round.

The Godfather

it will be a fluke if your boys manage to find them

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