insulation resistance testing bombshell

[apprentice87]

Hi All,

I am only a newbie, with not much experience at all, but anyway, i will just jump in with my observations!!!

First off, it seems to me that the original "source" of all this, [the bloke that has his name in the big red or green book] is a nitpicking know it all, trying to "show off" how superior his vast knowledge is compared to everyone else's.

Now, if i install a circuit, be it an extension to an existing one, or an entirely new one, or in the case of you lot rewiring houses, [i have never done this] a whole group of circuits I ALWAYS do an IR check on the bit i have installed [each individual circuit i have fiddled about with] BEFORE connecting ANY of it to the existing circuit or DB [or CU in the case of you lot doing the houses]

I do this to check out the new cable i have installed, [faulty cables do exist] and all the other bits i have installed too, for two reasons;

1, Just for my own piece of mind.

2, When filling in the certs, you are asked to record IR values for EACH INDIVIDUAL circuit. How you going to do that unless you test "your" circuit "on its own" before connecting it all up??? As an asides, although there is a column for this on the certs, i cannot find ANY reg that requires you to test each individual circuit.

Next, i will connect it all up. AFTER doing this, i will do a GLOBAL IR on the entire installation. This fullfills 3 objectives.

1, You are testing the installation "as installed" this is VERY important, as, if you just test the individual circuits [with or without their cpc's connected] you could introduce faults when you finally assemble the rest of it.

2, If, when you do the global, you then find a low reading, you then only have to disconnect "your bit" and re- test, to find out if the fault was already there, or if there is a problem with "your bit" after all.

3, To do a global is a [the only??] REQUIREMENT OF THE REGS.

Here is what the regulations concerned ACTUALLY say;

612.3 Insulation resistance.....

612.3.1

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



[Note how there is absolutely NO reference to testing INDIVIDUAL circuits here at all, cpc's connected or not, so we can only assume that it relates to a global, in which case, of course the cpc's will already be connected, especially as the ONLY figures given in the regs for minimum IR, are given in table 61, which SPECIFICALLY refers, by operation of reg 612.3.2, to global testing...

Let us look then, at the following paragraph [which is presumably intended to be read in conjunction with the one above]......

612.3.2

The insulation resistance measured with the test voltages indicated in table 61 shall be considered satisfactory if the main switchboard and each distribution circuit tested separately, with all its final circuits connected but with current using equipment disconnected has an insulation resistance not less than the appropriate value given in table 61.

This obviously refers SPECIFICALLY to a global, when the cpc's will obviously all be connected, and likewise, the figures given in the table to which this paragraph refers obviously relate to the test done globally, in which case the cpc's are obviously already connected to the earthing arrangement.

NOTE IN PARTICULAR HOW THERE ARE NO FIGURES GIVEN FOR VALUES FOR INDIVIDUAL CIRCUITS AT ALL just for "each distribution circuit tested separately, with all its final circuits connected but with current using equipment disconnected"

So, by merely doing a global, [which is all the regs require] you are automatically "testing with cpc's connected" Which is what the nit picking "know it all" concerned is refering to.

So.....unless 99 percent of electricians do not do a global on completed installations, 99 percent of "experts" do not know what they are on about....................

You all do globals [or at least i hope you do!!] so you are all doing it to the regs, and you are all doing it right!!!!

So, you all just keep on doing what you are doing, actually DOING the work, and not merely talking clever about it... Good for you lot!!!!!

john....

 

[TonyCE]

If you have RCBO's do you still do global tests? I find they tend to show a low IR if the live/neutral conductors are attached, but I am happy for the CPC to be "connected to the earthing arrangement". Thanks to the doctor for bringing this to our attention.

 

[sparkrow]

I thought that that was common knowledge !

---------- Post Auto-Merged at 11:42 ---------- Previous post was made at 11:41 ----------

I never do global test, I like to know that each circuit has its own integrity. Same goes for RCD Testing, it provides a confirmation that each circuit will make the RCD respond appropriately.

---------- Post Auto-Merged at 11:53 ---------- Previous post was made at 11:42 ----------

For Clarity, when I say I never do a global test, I mean for verification of a circuit just worked on. Before Everyone jumps all over me !

 

[apprentice87]

Yes, i agree!!!

Do them individually one at a time as you are installing them, and then a global as a final check when all is completed. That way you ARE complying with the bit about testing with the cpc's connected too!!!!

Thought this was what you were meant to do!!!

john..

 

[SPECIAL LOCATION]

Yes, i agree!!!Do them individually one at a time as you are installing them, and then a global as a final check when all is completed. That way you ARE complying with the bit about testing with the cpc's connected too!!!!

Thought this was what you were meant to do!!!

john..

Tis what I said back @ post #26

AT THE DISTRIBUTION BOARD WITH ALL FINAL CIRCUITS CONNECTED...you only separate them off if you have lowish readings and you are trying to eliminate latent defects...

All final circuits connected means all the CPC are still in the earth bar!?

That is how the GN3 and OSG have always described it.

However you do have the contradictory loop whereby..

a) You are told to test globally distribution circuit (+ DB & final circuits) but not individually final circuits...

But

B) If suspect latent defects lowering the global reading you are told to test individually...

c) Also if a complex installation you are told that may need to subdivide down into component parts... {GN3}

So....

You are NOT told to test individually..

unless you have to...

In which case you are to test individually!!!

] Guinness

 

[apprentice87]

Exactly!!!!

And if you test globally as instructed, then obviously all cpc's are connected!!

Where is the problem!!

john....

 

[sellers]

If you test globaly and you get a result you are happy with there is no need to test individualy.

Whats the point in splitting up circuits on a new build if the come in at >200Mohm globally depending on your tester

Also whats the point in splitting them up on a PIR if you reach a reading you are happy with for the age of the installation, say 50Mohm. Which is a very good reading globally

Maybe getting down to the low numbers you may wish to split to see which circuits are degrading the most, but strictly theres nothing wrong with doing a global IR and getting 2Mohm and leaving it at that, but I wouldn't

Just because there is a box per circuit doesn't mean it has to be done individualy, theres boxes for RCD's but if you have 1 covering 5 circuits you don't test it for each circuit.

 

[Nicky Tesla]

Hi All,First off, it seems to me that the original "source" of all this, [the bloke that has his name in the big red or green book] is a nitpicking know it all, trying to "show off" how superior his vast knowledge is compared to everyone else's.

HEEE HEEEE HEEEE LOL Sounds Like ME:slap

 

[Sidewinder]

What, Nicky are you a show off whose name is on a book? ] :slap :innocent ; )

 

[NozSpark]

What, Nicky are you a show off whose name is on a book? ] :slap :innocent ; )

Of course his name's in his book,,, he wrote it there with his crayons

 

[Manator]

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

 

[Sidewinder]

Where M?

 

[Manator]

Where M?

I edited my post whilst you replied Sidewinder and for those who do not know me 1 is the first name listed from the top. So when I said my first is in 5 it is not literal.

 

[Sidewinder]

M,

I meant where are you on about?

7671, GN3, the Part P Doctor or what?

 

[Manator]

Sorry mate I meant BS7671 BGB

 

[Sidewinder]

I'll check you out tomorrow, not going out in the cold & dark now to the van!

 

[NozSpark]

M,I meant where are you on about?

7671, GN3, the Part P Doctor or what?

Well you know I'm in that one

 

[SLIPSHOD & SLAPDASH]

Theres only a few with no E

 

[the doctor]

Hi All,

To clear up confusion with members, let me expand. In my book, I do exactly as I have always done. I hate disturbing the wiring for testing so test as I connect. My book photos show.

1 Rough schedule on wall nest to board

2 I strip ring conductors and do continuity test on long tails

3 I enter figures on sheet

4 I do IR test on long tails

5 I write figures on sheet

6 Finally, i dress in the conductors and terminate... JOB DONE

The BS7671 committee man pointed out that I am not doing it to 612 and if a conductor had a fault to earth somewhere, I would not detect it with the cpcs NOT CONNECTED.

I have always prided my self on doing the job 'right' and after arguing with him initially, I conceded defeat...

Now after some thought I have concluded that it really is important and wonder how I got to 47 without knowing/being shown/realising my shortfall.....The doctor has let himself down :red card

 

[apprentice87]

Hi There,

Yes, but how are you NOT doing it to the reg concerned???? There is nothing in the regs that says you have to test circuits individually as you are doing, [and as anyone with half a brain would also do] so the reg concerned does NOT apply to what you are doing [individual circuits]. The regs DO require you to carry out a global test, and the figures they give for the resistance of the insulation specifically refer to global testing.

So, as long as you do a global as a final check when all is finished, not only have you complied with the regs, [as when you do a global obviously all the cpc's are connected in the earth bar] but you have done EXTRA testing, over and above that which is strictly required..

So long as you do a global, you are being EXTRA fussy, not "doing things wrong" !!!!!!

Obviously this all relates to initial verification of a complete install. I will concede that if you were to test one circuit in isolation, [say as part of finding a fault] then to comply it would seem that you should leave the CPC in the earth bar...

Well, this is how i see it....Comments please!!!!!

john