Insulation Resistance??

rocker · Aug 13, 2010

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 · Aug 13, 2010

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

rocker · Aug 13, 2010

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 · Aug 13, 2010

ezzzekiel said:
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 · Aug 13, 2010

keithsims said:
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 · Aug 13, 2010

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 · Aug 14, 2010

rocker said:
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 · Aug 14, 2010

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 · Aug 14, 2010

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.'?