We racked our brains for ages over this and in the end have left it but it's still niggling me and I wanted to see if anyone could shed some light on it (I'm probably being thick)
We just had a small job to extend a radial to add in a couple more sockets, it's in a school so the board is the usual mismatch of circuits from the last 40 years. All went fine until we came to test with the fluke, when we got a very low reading testing insulation between phase and neutral.
Phase - Earth was 19MOhm
Neutral - Earth was 19MOhm
Phase - Neutral read as 0MOhm
Running a resistance test we found that there was a resistance of around 40Ohm between the phase and neutral.
After trying everything we could think of I decided to test some of the other circuits and half of them had the same dodgy reading. I disconnected the neutral feed to this board in case the problem was being picked up from elsewhere in the school but it made no difference.
In the end all we could do was test our side of the new installation (which was spot on) and let the school know that it could do with being looked at.
Could this be as simple as we'd missed unplugging something on the circuit somewhere or has anyone else got any more ideas? We're back tomorrow to do a different job so would like to have another look at it if possible.
We just had a small job to extend a radial to add in a couple more sockets, it's in a school so the board is the usual mismatch of circuits from the last 40 years. All went fine until we came to test with the fluke, when we got a very low reading testing insulation between phase and neutral.
Phase - Earth was 19MOhm
Neutral - Earth was 19MOhm
Phase - Neutral read as 0MOhm
Running a resistance test we found that there was a resistance of around 40Ohm between the phase and neutral.
After trying everything we could think of I decided to test some of the other circuits and half of them had the same dodgy reading. I disconnected the neutral feed to this board in case the problem was being picked up from elsewhere in the school but it made no difference.
In the end all we could do was test our side of the new installation (which was spot on) and let the school know that it could do with being looked at.
Could this be as simple as we'd missed unplugging something on the circuit somewhere or has anyone else got any more ideas? We're back tomorrow to do a different job so would like to have another look at it if possible.