Insulation Resistance??

[rocker]

Yea, that's what I'm saying. But if, as is being suggested here, we should not be testing individual circuits and should be testing at the bars, then doing this will mean that we are testing every other circuit, and not the one we have worked on. If I am testing an individual circuit, I:
open breaker
D/C line
Find N and CPC for circuit and D/C those
Test L1 and L2
Test L2 and LN
Test LN and L1
Look for missed neons
Test Ln and L1
Reconnect and enliven.

If we left all the CPCs in the earth bar, and all the neutrals in the neutral bar, and the rest of the installation is turned on, then we are going to get very duff readings from where the Neutral and Earth are connected somewhere on the other side of the main isolator (PME, anyone?).

These are my thoughts, anyway.

 

[Adam W]

Surely the main isolator (DP) would be off though, otherwise you'd be trying to do IR live?

 

[rocker]

No because the breaker would be open (off) and all the wires would be disconnected from the board altogether. All the other circs will be live, but the one I'm working on will be deader than dead.

 

[keniff]

its also advisable to disconnect the circuits neutral or earth

i have always been told to leave the earth connected as this would pick up any problems related to structural earthing/pipes etc

 

[Risteard]

i have always been told to leave the earth connected as this would pick up any problems related to structural earthing/pipes etc

It should be connected to the means of earthing.

 

[Jimmy Boy]

Are RCD's/RCBO's able to with stand a 500V test ? I refer you to GN3 test 2 on page 38 which states that simple installations should be tested as a whole, and IF a reading of less than 2M ohm is recorded then the circuits should be tested individually

 

[Adam W]

No because the breaker would be open (off) and all the wires would be disconnected from the board altogether. All the other circs will be live, but the one I'm working on will be deader than dead.

I'd always been told not to work on a board live, even taking the cover off, because it exposes live parts.
Any parallel paths should be taken into consideration because they will be present when the circuit is used.

 

[Benny_Boy]

IR is a dead test, surely??? I wouldn't fancy scratching around in a consumer unit with the busbar exposed if the thing wasn't proved dead!

 

[rocker]

The busbar wouldn't be exposed. The cables for the circuit would be disconnected as I keep saying.
Surely if this is the wrong way to test, there is no need to have access to the screw terminals in the top of an MCB, so why aren't they put behind the shield that covers the busbar.

Are you guys seriously telling me that if you replace a lighting pendant that you power down the whole installation? Or do you just not bother to test/certify?

And as someone else has said, I would be very dubious about putting 500V through an RCBO. I understand testing in many circumstances from the neutral and earth bars, but I have never seen or heard of testing from the line busbar in a consumer unit. It just seems like madness to me. What do you do if you find a fault, just say 'oh, there's a fault somewhere on the system. Oh well.'?

 

[rocker]

It should be connected to the means of earthing.

I'm not being funny, but are you confusing an insulation resistance test with an earth fault loop impedance test?

 

[Des 56]

I but surely it suggests that there is something not quite right on one of the circuits?

Best to ask yourself why we do the insulation test

eg
What are the effects of heat ,age, mechanical damage etc and what they mean to the results of the insulation test that is being done on your installaton

 

[Jimmy Boy]

Does anyone/Has anyone used test method 2 in GN3 as stated in regs book 612.3, where to join the 2 Line conductors together and test to earth ? this removes the need to disconnect sensitive equipment and must be quite useful if you have a circuit full of fluorescent lights or similar.

 

[semaphore]

Steve,
"Does anyone/Has anyone used test method 2 in GN3 as stated in regs book 612.3, where to join the 2 Line conductors together and test to earth ? this removes the need to disconnect sensitive equipment and must be quite useful if you have a circuit full of fluorescent lights or similar."

We use this method virtually all the time. I'ts very rare we can disconnect equipment.
I think you mean join the line(s) and neutral together and IR test between the live conductors (joined together) and Earth.

 

[Jimmy Boy]

Thats what I meant yes I was calling the Neutral a Line conductor I should have said 'Live' conductors

 

[Risteard]

I'm not being funny, but are you confusing an insulation resistance test with an earth fault loop impedance test?

No, I'm not.

Insulation Resistance should be performed with the system de-energised and the means of earthing attached.

 

[Risteard]

What do you do if you find a fault, just say 'oh, there's a fault somewhere on the system. Oh well.'?

You open circuit breakers or remove neutrals until you find the faulty circuit. That is why it says that below 2 Megohms requires further investigation. This is the further investigation.

 

[rocker]

You open circuit breakers or remove neutrals until you find the faulty circuit. That is why it says that below 2 Megohms requires further investigation. This is the further investigation.

Which, for the billionth time, is what I do to start with, because, for the billionth time, there is no need to test the full installation if you are only working on one circuit.

 

[rocker]

Just realised my last post comes off as really chippy, which was not what it meant to sound like. Just find it odd that we've all been taught in different ways.

 

[Risteard]

Which, for the billionth time, is what I do to start with, because, for the billionth time, there is no need to test the full installation if you are only working on one circuit.

I'm not talking about working on an individual circuit.

I am pointing out that insulation resistance is cumulative.

And no need to apologise.