Eicr insulation resistance testing

[GarryJ]

Hi All.

I am currently carrying out an EICR in a local hotel. I was wondering how each of you carry out insulation resistance testing during a periodic inspection?
For lighting etc I have used joining live-neutral together and testing to earth due to the unknown possibility of electronics and lamps etc throughout the circuits.
It is an old Dorman Smith DB 3pH and I turned off the main switch of the DB which powered the full insulation down then disconnected the main earth from the isca block which was coming from the TNC-S cable head. I was getting a dead short between this isca block to the neutral bar of the DB after this earth was disconnected. I am aware back at the transformer earth and neutral are connected but once the main earth is removed I thought it would have been clear?
Would parallel paths cause a dead short? I.e the main bonding to water and gas?


Thanks in advance for any help with this

Garry

 

[Simlec]

All earthing should remain in place when conducting IR tests.

 

[SirKit Breaker]

All earthing should remain in place when conducting IR tests.

Why? and what do you do if you get a out of spec result when testing at the tails?

 

[Tidy Max]

So the neutral is still connected, and your testing a TN-C-S between the incoming neutral and MET and getting continuity?

 

[GarryJ]

Yes I have disconnected main earth band going from cable head to isca block where DB and bonding are connected into and I am getting dead short between isca block and neutral bar in DB. Am I missing something

 

[Simlec]

Why? and what do you do if you get a out of spec result when testing at the tails?

How would you find a fault between L or (normally) N and say some pipe work in the building if you start disconnection earths.
As for testing at the isolated side of your iso and you get poor results (the norm) you would sub divide the install but still leave all your earthing connected.

 

[andyelectric]

I am in agreement with Simlec.

 

[Simlec]

Garry, is there not a neutral link bar in the DB? as it sounds like its a 3 pole iso.
& yes testing with L-N to earth is fine.

 

[mossep]

Sound like you have left the main neutral connected, you need to remove the link or disconnect the neutral conductor from the bar.

All earths are left in place when IR testing unless you are testing an individual circuit.

 

[Simlec]

Sound like you have left the main neutral connected, you need to remove the link or disconnect the neutral conductor from the bar.

All earths are left in place when IR testing unless you are testing an individual circuit.

Your CPC will still need to be connected to MET when doing a single circuit or how else would you find the fault i said earlier.

 

[mossep]

Your CPC will still need to be connected to MET when doing a single circuit or how else would you find the fault i said earlier.

Test to the main earth bar as well.

 

[Simlec]

Test to the main earth bar as well.

lol If you wish, more tests to do or you could just leave it connected to earth bar.

 

[tony mc]

What do you mean re a dead short are we talking 0.00 Meg Ohms or 0.00 Ohms or could it possibly be K Ohms ?

If you are testing the entire installation at the tails and if only one circuit is low it will bring your reading down!

You will have to start testing each circuit on its own until you find the circuit / circuits !

 

[GarryJ]

Cracked it!! I have forgot to remove the link before testing. For all the individual circuits I have tested I have removed the neutral and CPC from each of the bars and then carried out IR but just when testing the mains I have forgot to remove the link. If no link is present removing the main neutral and testing from the MET to the neutral bar with all circuits neutrals is correct?

Thanks

 

[TJ Anderson]

So it was basically a 3 pole main switch with solid neutral which you had left connected whilst carrying out your insulation tests. Guess you have not done much testing on 3 phase systems.

 

[tony mc]

Why are you removing the CPC from the earthing arrangement or have I misread that ?

 

[yellowvanman]

Why? and what do you do if you get a out of spec result when testing at the tails?

Because 612.3.1 tells you to!