Voltage between Neutral and CPC

[Will Sykes]

I was called over to check out why some corridor lights kept tripping out. They are all on klik roses, wired in singles inside metal trunking. I turned the circuit off and disconnected all cables in order to test for insulation resistance. Before i even got a chance to test, i found that the voltage between Live and Neutral was 189v, between Neutral and cpc was 215v and live to cpc was 0v. Any ideas why i could be experiencing these voltages? At first i thought there may be a shared neutral somewhere.

 

[telectrix]

sounds like a floating neutral or something like. isolate compete board and then do dead tests. check for cross connections between circuits and for any open circuits.

 

[Marvo]

Most likely a shared neutral, I would expose the entire circuit if it's in trunking, the fault should be easy(ish) to find.

 

[NrVolts]

"live to cpc was 0v" i would suggest there is a broken connection in phase or cpc or both.dead test is the first thing i would do ..wander lead to check continuity or short R1 TO R2 in Board and test from a mid point to split the circuit in half.so you know which half has the fault.
please feel free to comment im not an expert even some +ve feedback would be nice.

 

[NrVolts]

ah maybe best ignore last comment ..you got 215 between N - E .Sorry.

 

[Will Sykes]

found the fault. indeed someone had pinched a neutral for two neons in a bank of switches. didn't notice it at first as the switches were not for the lights at fault. problem with where i work is that it is for a pharmaceutical company and therefore most things cannot be turned off without it being planned into our six monthly shutdown periods.

 

[NrVolts]

good grief.that cant have been easy to find.not usual is it to find any neutrals in a switch bank.even harder for practical terms without been able to turn things off.Cant you even isolate power out of normal working hours?
If i was the maintenance manager i would have been very impressed by your diligence.

 

[Will Sykes]

cant isolate any power outside of shutdown because we need our air handling units running to keep our production areas sterile!