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Topic Title: Advice with EICR
Topic Summary: bad insulation testing readings
Created On: 03 October 2013 09:18 PM
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 03 October 2013 09:18 PM
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tillie

Posts: 801
Joined: 03 May 2006

Hi , I am currently carrying out my first industrial EICR on a unit on a trading estate.

Brother in law phoned me to say that he had been quoted 3k over the phone by one contractor and three hundred pounds by another contractor and would I please do it it for him.

So here I am.

It is a big empty warehouse with toilets and two floors of offices.

Supply comes in to a 3 phase 100 amp head over to 100amp Mem switchfuse and up to an eight way 3 phase Memshield board.

This board feeds the toilet lights and some spurs and sockets.

It also feeds another board in the offices that looks like the original board for the warehouse.

I carried out earth continuity to all these circuits on the first board and all was good.

I then decided to do a global insulation resistance test with all live conductors connected together (including neutral ) to earth , but I switched the main switch off on the office board so as not to include all the final circuits on that board for the time being. I also disconnected the neutral.

My megger was showing 3Mohms so I was not very happy.

I had a bit of time so I started to find out why.

I located the low reading to the sub main which feeds the office board.

It is a 10mm 4 core micc cable ( looks very old ).

I completely disconnected this cable and tested all on its own .

Definetely 3 Mohms.

It was at this point that I was going to ask the question " should I fill all the boxes on the report regarding insulation testing with this reading 3 Mohms even though all the other ccts were fine.

I then moved onto testng the office board.

Main switch off , neutral disconnected and global IR on the board so as to include all final ccts.

0.00 Ohms. Found that low reading is between neutral and earth.

I lowered the scale on the Megger it it is reading 63 ohms !.

So it seems the low reading on the sub main cable is the least of my problems.

I have been askedto try and find the problem.

So my question really is apart from disconnecting all the neutrals one by one which will be a nightmare due to the state of the board is there anything else that could cause such a low reading .

There are about 60 recessed 600 x 600 fluorescent fittings , water heaters and pumps and about 12 2D fittings.

Advice appreciated.

Regards
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