Flying earth fault?

[frecossais]

Hi guys first time posting on here, so here is my question. I work in street lighting and I've got a fault to repair tomorrow. Just want to seee what other sparks think about it. Anyway when I disconnect a column in this certain gircuit (loop-in, loop-out) then one end of it has got juice in it even though the pillar is switched off. When I mean power, there is voltage between phase & earth , and neutral and earth although there is no voltage between phase & neutral. Also the voltage is fluctuating between about 17 &205 volts yet when I connect the circuit back together it disappears. I thnik maybe a flying earth fault although I'll know more about it tomorrow when I go to see it but I was just looking for other opinions on this fault. Cheers

 

[markythesparky]

you are getting a feed through all the other fittings on this circuit and back along the neutral. Because you haev disconnected the neutral there is no where for the voltage to go so it will be at mains level. This is why there is no potential difference between the phase (at 230v) and the Neutral (also at 230v until conected again)

As soon as you reconnect it you are allowing the Neutral potential to go to earth and therefore 0.

The fluctuation in voltage could be to do with the photocells on the fittings. are you disconnecting the CPC on the circuit when doing this. if so you are removing the earth and therefore you will get very odd readings.

 

[frecossais]

Hi Marky thanks a lot for replying to my question. Today I went to see this fault and after a little bit of time I discovered what the problem was. At the pillar(d.b.) just at the service head cut out someone had taken a supply to feed another pillar which in turn fed 20mph school flashing signs.The problem was that they had connected the neutral for this feed directly into the neutral block for the street lighting circuits rather than into the service cable head. So that meant that when I switched off the main switch then there was no return path for this neutral which fed the other pillar.So i disconnected it and reconnected directly into the service head cut out and the problem was solved.
Thanks again for your view on this problem.