Earth Wire Query

[wreck-it-steve]

Hi,

I was changing a light switch yesterday as it was broken and noticed when I was putting the earth wire in to the light switch earth terminal it was ever so slightly sparking... is there any reason why this would happen or do I have an earth fault?

Thanks

 

[STEVEROG]

That doesn't sound good.

I suggest you get a sparky in to have a look.

It is possible for poorly grounded earth conductors or any lumps of metal to 'float' up to hundreds of volts. Fault current flowing back through the earthing wire and then through the fault device will only cause a 'trip' if the fault current is beyond the trip point, typically 30 mA for domestic bog standard RCD protection.

Your 'sparking' wire could be either the metal box floating up at hundreds of volts or the earth wire. Your system may not be tripping your RCD as you may not have RCD protection? or your problem circuit is not on the RCD protected side of your board? or the leak current isnt quite high enough to trip out. In any case, you need a sparky before someone gets fried!

Steve

 

[ricicle]

Or it could be that the walls were slightly damp and there was a very small potential difference between the electrical earth in the cable and true earth to which the switchbox was part of due to the damp.....

 

[westie101]

What type of earthing has the property got? This could be as a result of a net current.

 

[wreck-it-steve]

Hi,

The cut out / service head is boxed in so im unable to get to it but its earthed from the neutral via a 10mm earth. The spark was not bad but enough to notice.

Thanks

 

[westie101]

The cut out / service head is boxed in so im unable to get to it

An aside but it should not be, it ever needs replacing or goes faulty how do you expect DNO staff to work on it?


If it is TNC-S (PME) net currents in the neutral are always a possibility, if it is these there is no real issue or risk.

See this: -
http://www.emfs.info/Sources+of+EMFs/distribution/