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Why did I get 50v when I turned the fuse-board off?

Charles Newey

Even pulled the fuse out the kmf but still got 50v between earth and neutral. When i energised the fuseboard back up the voltage went. Had a high ZE. And a high PFC. 
however the RCD wouldn’t operate. I have noticed 15/20v’s at multiple different properties in the last 6 months but today. I felt the volts when changing a socket. Do we need to start disconnecting all cables before we change a socket or light etc. does there need to have more earth spikes fitted on property’s. No engineer should get a shock it’s they turn off the mains. 

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    What's the Earthing system? A fair voltage difference between N and PE is perhaps expected on TT systems (hence the requirement for DP isolation on TT). There shouldn't be a significant difference on TN-C-S (PME) though - as the two should be one and the same at the cut-out. TN-S would be a bit in the middle.

    What sort of instrument are you using and are there any live parts remaining in the vicinity - capacitive coupling can sometimes result in an apparently significant voltage appearing on isolated conductors which can be read by high impedance (electronic) voltmeters, but disappears as soon as a relatively low impedance (e.g. a human) shunts it. Probably not the case if you felt something though.

    No engineer should get a shock it’s they turn off the mains.

    One of the reasons all main switches in single phase domestics are double pole! (You should always be testing for dead in any event).

    Some DNO faults can give nasty effects - damaged N or PE can be dragged up to a higher voltage by connected loads (either normal L-N currents or earth leakage) and uncleared L-PE elsewhere on the network can result in N and/or PE being a lonq way from the nominal 0V they should be.

       - Andy.

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  • 0

    What's the Earthing system? A fair voltage difference between N and PE is perhaps expected on TT systems (hence the requirement for DP isolation on TT). There shouldn't be a significant difference on TN-C-S (PME) though - as the two should be one and the same at the cut-out. TN-S would be a bit in the middle.

    What sort of instrument are you using and are there any live parts remaining in the vicinity - capacitive coupling can sometimes result in an apparently significant voltage appearing on isolated conductors which can be read by high impedance (electronic) voltmeters, but disappears as soon as a relatively low impedance (e.g. a human) shunts it. Probably not the case if you felt something though.

    No engineer should get a shock it’s they turn off the mains.

    One of the reasons all main switches in single phase domestics are double pole! (You should always be testing for dead in any event).

    Some DNO faults can give nasty effects - damaged N or PE can be dragged up to a higher voltage by connected loads (either normal L-N currents or earth leakage) and uncleared L-PE elsewhere on the network can result in N and/or PE being a lonq way from the nominal 0V they should be.

       - Andy.

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