insulation resistance testing bombshell

[ProDave]

I do as the doc says and test each circuit cables individually before terminating.

but THEN when all is connected and CPC's terminated, I do a global IR test L-E and N-E

THAT final test would show up the L-metal framework fault referred to above.

 

[the doctor]

Pro Dave has the way forward.

It could do with going in to GN3 and the OSG written exactly like that as well

 

[Sidewinder]

IIRC I stated that back in post #10

 

[the doctor]

sorry sidewinder...

Of course you are correct... in all the confusion I missed that... i am still reeling from the embarrassment!

 

[Nicky Tesla]

My name is included on page 10, I could run a competition to see if any member can find it.Its not a joke I am really there but I doubt any of you could ever find out what my name is.

OK I will give you some clues

My first is in 5 but not in 1

is your name Reg (short for Reginald)

 

[professional]

I`ve read through all of the post in this thread and I seem to be missing something ....

612.3 Insulation resistance

612.3.1 The insulation resistance shall be measured between live conductors and between live conductors and the protective conductor connected to the earthing arrangement. Where appropriate during this measurement, line and neutral conductors may be connected together.

This seems pretty conclusive to me - how the hell can you carry out an IR test between Live and earth if the CPC`s aren`t connected to the reference potential of earth - it`s like claiming that you have carried out a polarity test without earth potential present ....

It is important to distinguish between testing cores in a cable for electrical separation from each other and for separation from the general mass of earth.

In such instances as mentioned, a cpc is merely a cable core until it is connected appropriately.

 

[batty]

I always thought you are testing the insulation resistance of the cable IE if the cables insulation is breaking down but I may be wrong. Well this is part of what you are testing for anyway.

 

[professional]

Insulation testing is carried out to verify both the electrical separation of the cores AND to ensure that only the CPC is connected to the general mass of earth on the consumers side.

 

[batty]

But surely when you do your loop test this will verify that the CPC is connected to the general mass of earth.

 

[apprentice87]

I am with Batty on this one;

I always thought you are testing the insulation resistance of the cable IE if the cables insulation is breaking down but I may be wrong. Well this is part of what you are testing for anyway.

The testing with the cpc connected to earth will be done automatically when you do your global test, which is what you will have to do anyway, as otherwise, you are doing your FINAL testing with the installation still "in bits" as it were, you know, BEFORE the installation is complete.

Besides, not our fault if the regs people cannot write properly;

Where it says;

612.3.1 "The insulation resistance shall be measured between live conductors and between live conductors and the protective conductor connected to the earthing arrangement. Where appropriate during this measurement, line and neutral conductors may be connected together"

surely it SHOULD read something like;

612.3.1 "The insulation resistance shall be measured between live conductors and between live conductors and the protective conductor WHILST connected to the earthing arrangement. Where appropriate during this measurement, line and neutral conductors may be connected together"

john...

 

[sellers]

personally I don't see what the fuss is all about, it makes sence to be,

test your IR with the CPC connected to the earthing arrangement, simples. You really shouldn't be testing an installation before its complete. So once its all done and in place, remove your lines and test to earth.

The same applies in reverse for you R1+R2, remove your cpc from the earthing arrangement.

 

[ProDave]

You really shouldn't be testing an installation before its complete.

The exception being if you suspect some cables may have been damaged (i.e you have lost confidence in the builder) and you want to find out if all the cables are still okay before it's to late to fix any damage without a LOT of rework.

 

[the doctor]

Hi Sellers,

Unfortunately the OSG and GN3 show a link connecting line and cpc with cpc in earth bar..

 

[brav]

Anyone else noticed theyve taken the 'below 2M ohm needs further investigation' out of the new GN3?

Very interesting thread by the way.

I like the Unite ELECTRICIANS GUIDE TO INSPECTION AND TESTING with 1st ammendment, all testing i do is based exactly the same as in this book, so with this and my GN3 which has more on 3phase i hope i'm on the right track.

If anything unfortunate happens to any of my customers they'll be receiving a strongly worded letters from me.

As my lecturer always tells me, these books explain to you the MINIMUM requirements to comply with the regulations, so if you feel you need to test more as long as your not causing a defect by the extra work its fine?

 

[the doctor]

Hello All

Thanks for the replies.

I was at college the other day and found a regs book from 1997. It says you test between live conductors and between live conductors and earth.

No mention anywhere of cpc connected to system earth. This means....

In 81, I was taught the way I was taught... The way I did it till a fortnight ago.

In 97, I was still doing it right, just as the big book in college says.

Now I do not know when they changed the wording....so the best I can comment on now is...

In 07, I wrote my first book with my 'old and possibly wrong' method - four figure sales and no one commented.

In 09, I amended it to the BRB with the same old IR testing which was now definately wrong- double the first sales and no comment.

In 12, I am having it proof read by one of the committee guys on p10 of the BGB. He tells me I am wrong! Me, a doctor? Of course I love a good debate and ask him to prove this to me, which of course he explained in detail...

I have spoken to a few sparkies and my revelation is also a revelation to them, so it appears....

That the IET changed the wording to reflect some sort of scenario that they had thought up or had reported. That is fine, however, they never bothered telling anyone about it:innocent

 

[Manator]

I can offer you some support on this one, I also checked out the wording and you are correct, I have by habit if nothing else always disconnected the cpc from the earth bar for this test, and afterwards done a global test with all bonding and cpc's connected, but that is just overkill on my part.

 

[brav]

Does anyone disconnect the bonding when doing a continuity of main bonding when doing a EICR?

 

[steptoe]

I think you would find that that is the only way to actually verify it.

headbang

 

[brav]

whats with the head banging?

i would do the same, but there are inspection and testing books now sayng there is no need to remove the main bonding conductor when testing an exsiting installation, ie EICR

If the worst happens as like the OP's sineario and we end up in front of a lawyer with these books in front of us going through all the tests we did, i would have said i disconnected the main bonding to take a measurement and he/she would show me a book based on BS7671 saying i shouldnt.

 

[Zeespark]

If you don't disconnect Brav, you would get parallel paths.

AndyGuinness