Shock query

[Bahco]

I fitted a brass dimmer (making sure to earth the case) and it worked fine but as I was fitting a plastic switch cover I got a shock

I realise I should have turned the power off now but am wondering why the case became live and gave me a belt. Could it have been a loose connection perhaps?

 

[cumbriahandyman]

Isolate and take the switch off. See what has happened.

 

[bernardgreen]

Could it have been a static electric shock? If you had become charged with atatic electricity from a carpet or nylon underwear then when you touched the earthed metal switch you would discharge.

Short sharp short = static.
prolonged buzzy shock = dodgey electrics.

 

[Bahco]

Isolate and take the switch off. See what has happened.

No sign of any damage but have put a regular switch on just in case and have put the offending one elsewhere with no problems.

 

[Taylortwocities]

I fitted a brass dimmer (making sure to earth the case) s?

So, what checks did you do to confirm that the earth connection was actually connected to earth?
Just because there is a conductor does not mean that it is connected properky or to anything.

 

[Bahco]

So, what checks did you do to confirm that the earth connection was actually connected to earth?

I earthed the brass casing by connecting to the existing earth in the supply cable which was screwed into the knockout box.
I assumed that the sparky who put in the new circuit 8 yrs ago would have ensured that the earthing was done properly.

 

[Paul_C]

I earthed the brass casing by connecting to the existing earth in the supply cable which was screwed into the knockout box.
I assumed that the sparky who put in the new circuit 8 yrs ago would have ensured that the earthing was done properly.

You would hope so, but unfortunately that's not always the case. It's not that uncommon to find that what started out as a 1960's installation with no earth on the lighting circuit has been extended in more recent times using T&E which has an earth conductor (since that's all that's available now), but that the earth conductor isn't actually earthed anywhere. It might be connected between the various boxes, metal switches, and light fittings on the new part, but not actually connected back to the earth bar at the distribution board.

Or it could be that the lighting circuit does have an earth conductor throughout, but that there's a bad or missing connection on it somewhere.

 

[Bahco]

Or it could be that the lighting circuit does have an earth conductor throughout, but that there's a bad or missing connection on it somewhere.

Thanks for the replys.

How would I test that the earth was connected?

 

[JohnW2]

Or it could be that the lighting circuit does have an earth conductor throughout, but that there's a bad or missing connection on it somewhere.

True. However, if the OP really did get a true (not static) shock, there would have to be something else simultaneously wrong - since the absence of earthing would obviously not, in itself, make the switch plate live.

Kind Regards, John.

 

[bernardgreen]

Use a volt meter with a long wander lead to measure the voltage between the earth terminal at the meter location and the CPC conductor in the switch box. Treat the CPC as hazardous relative to the wander lead until you have ensured there is no voltage difference between CPC and the earth terminal at the meter.

If there is any significant voltage ( more than a volt or two ) then the CPC is almost certianly not connected.

If the voltage is close to zero then try a resistance measurement between CPC and earth terminal at meter location. You may need to turn the main switch OFF to get a sensible reading using a multimeter as stray capacitive coupled currents will interfere with the resistance measuring circuit in the multimeter. Thes often use only a few milli-amps or even micro-amps to make the measurement and that current can be swamped by the capacitive coupled currents.

A high current ohm meter is the prefered method using half an amp or more as this will not be significantly affected by capacitive coupled currents.

 

[securespark]

Over 3 yrs now without smoking

Not even when you got the shock?