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Topic Title: electrical installation certificate clarification
Topic Summary: Block of flats
Created On: 30 November 2012 05:29 PM
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 30 November 2012 05:29 PM
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Hi , I am currently rewiring a flat which is in an old block of around fifty flats.

I have installed a new consumer unit and the client has arranged to have the meter moved.

Edf turned up yesterday but refused to move the meter due to the second fix not being complete ( fair enough ).

The Edf chap then told me it was down to me to find out where the flat was fed from etc.

After two hours of tracing out trunking and conduit runs throughout the flats and coming up against locked doors I found the sub board which feeds the flat on the fifth floor staircase landing.

Luckily it was open and I found a 8way 3 phase Ryefield board.

Also found the service head in the basement , this was renewed in 1998.

So I have a 300amp incomer (fuse size unknown )with 120mm tails to a 200amp isolator and a 70mm earthing conductor ( Tncs ).

From here I have a 4core 120mm swa feeding my Ryefield board on the fifth floor landing with 70mm cpc.

From here I have a Bs1361 60a fuse which feeds 16mm single cables which feed the flat.

All flats are the same.

I am fine with supply characteristics and earthing arrangements but what would be the particulars of installation at the origin.

Would this be the 200amp switchfuse in the basement or the 60 amp fuse on the landing.

What would be the main switch or circuit breaker , the 200amp switch , the 60 amp fuse or the 60947-3 switch in the consumer unit.

I would not normally be so concerned , I would use the 60 amp details but building control are all over this job because the builder did not notify anyone and has taken out walls and partitions and the neighbours have complained about the noise and the parking so alerting building control about the works.

Oak flooring has had to be taken up to fit a sound barrier , fire doors have to be added etc.

Electrical and gas certificates required obviously , but I know it will be scrutinised so I want to get it spot on.

Another point regarding Ze .

How ? I cannot turn off fifty flats.

Also bonding. If the supply in is 300 amps I dont know what size the incoming neutral would equate to but I have a 120mm neutral up to the Ryefield.

This makes me wonder if the 16mm earths that go into each flat comply because surely the bonding conductors if related to the incoming neutral should be around 35mm ( assumed ) .

Advice appreciated.
 30 November 2012 09:19 PM
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I would take it from the first part of the installation after the supply companies meter to your individual flat. All wiring before then is their reponsibility.


Specialised Subject. The Bleedin Obvious. John Cleese
 30 November 2012 09:40 PM
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Not necessarily their responsibility these days Gary, but I'd agree that the OP's installation starts from the customers side of the meter in the flat.

Most DNO's will disown the risers and associated distribution equipment but in this case I don't see that is an issue.

The incoming protective device is 60 AMPS BS88, The main switch is 60947-3 and assuming it's a normal supply the incoming earth conductor at 16mm and bonding at 10mm should comply (unless I've missed something)

 30 November 2012 09:59 PM
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Thanks chaps.

I take it that I will also take my Ze reading at the incoming terminals at the flat ?

 30 November 2012 10:07 PM
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Yes, It's the origin of your supply as far as BS7671 is concerned.


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