Insulation Resistance Testing (Whole board at the same time).

[seb77]

Lads,

I am soon to be doing an EICR on a large working mens club (not being paid in ale). My question is this...There is going to be lots of lamps i cant take out,equiptment still plugged in that i cant find etc etc so im gonna have to test between L-N to E .

When carrying out the IR test at the sub boards i want to try and test the whole board in 1 go. My way of doing this would be to isoloate the supply to the sub board im testing,disconnect the supply cable, then link out the main switch with a piece of 16mm2 cable and test to earth. Is this the way you boys would do it?. I know if i get a poor reading i will have to test each circuit on its own.

Any thoughts would be tremendous.

 

[Deleted member 26818]

You wouldn't need to disconnect the supply cable, if the switch isolator is double pole.
You may have problems with the earth conductor, if the system is TN-C-S.
Either disconnect the earth conductor to the board you are testing, or the main earthing conductor for the installation.
Then isolate the double pole supply switch at the board you are testing, link between the busbar and the neutral bar using a short piece of cable with a croc clip at each end.
Connect one probe to either the busbar or neutral bar, and the other probe to the earth bar, then press the test button for however long your particular tester requires.
Obviously, if the reading is too low, then you will have to test the circuits individually.
I would disconnect the live conductors for the individual circuit, place them in a large connector block, with one probe in the other side, connect the other probe to the earth bar and test.

 

[needasparks]

If you are only testing phase conductors to earth why bother linking out, just test L-E then N-E. it will give the same worthless reading with a mixture of earth leakage results.

 

[Edd]

If its single phase... main switch off. link the top of one mcb with the neutral bar, bit of 1.5 singe will do, all other mcbs on. then IR test between neutral bar and E.. remove link before switching on!! otherwise big bang!!

 

[Adam W]

I'd leave the earth in and turn the main switch off - you need the earth in to include parallel paths which will be present when the installation is energised.

I can't imagine you'll get a very good result though - as mentioned you'll also pick up any earth leakage from whatever equipment is still plugged in. I reckon you'll end up testing each circuit individually.

If there is a load of equipment still plugged in somewhere that would presumably also mean there are sockets which you can't find, so I'd probably test at 250v between live conductors as well, to put my mind at rest.

 

[seb77]

Cheers for the replies. The wiring looks a little old in places and install in general is untidy from what i cansee. Above 1sub board i can see a little "rodent damage" on a T&E. The last bloke who tested it got >999 on every test (mmmm)and didnt test any of the sub-mains.

Its a 3 phase TN-S system but all the sub boards are single phase.

 

[Engineer54]

Very difficult to undertake a meaningful global IR test on a large installation that is in use with lamps in, and as you say you can't find all the outlets etc!! Global IR tests are fine to check the likes of, small new-build domestic installations without any of the lamps in, and was the common method of testing domestic and other small installations in the past. But in your situation, your going to be far better off testing individual circuits, you'll just be wasting your time trying to global test a commercial premises of this size...

 

[ezzzekiel]

joining l/n and testing to earth is in most cases a pointless effort, earth leakage will still show up on some items of equipment left plugged in.

 

[seb77]

Cheers lads,

I dont want to cut any corners but want to get the job done as quickly as i can and 1 way of bringing the time down was to IR test the whole board at once.

There are quite afew single phase boards in the place with about 8 circuits on each with a mixture of MCBS and RCBOS.

its my 1st biggish commercial EICR so obviously i want to get things spot on. Do you think the best way forward for me is to remove all the lamps and unplug all the items i can find on each circiut then test at 250v between L-N and 500v between L-E and N-E?. I dont want risk banging 500v down incase ive missed somethin g and end up frying summot!!.

Cheers for all your replies...great as ever!.

 

[the pict]

I agree with the comments made, and probably best test as you go lights can be IR'd L&N to E and as said christ knows what,ll be plugged in, I once set off a alarm in a smoke machine ** I would also mention that a 3 phase board with an unswitched neutral supply cable will bugger things up as you will almost certainly have a constant E-N loop which will preclude an all in test unless you disconnect it but I would not advise it unless you can isolate it really well
Pict

 

[Richard Burns]

Probably the quickest way to test each board would be to test the whole board L+N to E at 250V and see what you get, if the result is nice and high then try a 500V. If you have a good result..done.
If you get low results on the 250 V then break the board down and test each individual circuit L+N to E (250V first then 500V if OK. This should be quite quick and if you have a good result then you are OK. if the results are still bad then you should be doing the remove all loads and test fully L-N, L-E, N-E.

Remember some RCDs and RCBOs say do not IR them!

 

[Engineer54]

Well i think it'll be quicker testing the individual circuits, especially as the OP states the wiring looks pretty grim in places. As i stated before, getting accurate/meaningful IR results using global IR testing of in-use installations is difficult. Your hamstrung before you start, having to test only between L/N to Earth...

 

[SirKit Breaker]

Don't forget, Inspection precedes testing. Have a good look at things long before you do any IR tests, you could end up making a bad job worse, and having to put things right at your own expense. if you consider that the installation will not be up to a 500v IR test, then dont do it, and tell your client why, if he insists, then make sure he knows the possible outcome. The first thing to consider with any test, is your personal safety. A test at 250v wont achieve a great deal, the idea is to put it under pressure, hence 500v.

Cheers............Howard

 

[Edd]

If its single phase... main switch off. link the top of one mcb with the neutral bar, bit of 1.5 singe will do, all other mcbs on. then IR test between neutral bar and E.. remove link before switching on!! otherwise big bang!!

LOL i dont remember wrighting this,, alcohol and advice!!!! should they mix?? I say YER