Hi,
I have now finished converting all my unearthed metal light switches to plastic as talked about at //www.diynot.com/forums/viewtopic.php?p=827868
Interestingly, it turned out that for two of the rooms (the bathroom and downstairs WC) we actually did have a T&E cable serving the switch.
They also had metal back boxes as opposed to the plastic ones used elsewhere in the house. (When I say plastic, I am talking about some kind of old-fashioned plastic ones for use in brick walls rather than modern dry-lining ones).
At both the bathroom and the WC, the cable was fairly modern looking with a single piece of copper for each conductor, rather than the three-stranded silver-coloured conductors used in the rest of the rooms. At the WC switch the earth was bare and at the bathroom it was sheathed in plain green (so presumably not that modern)
On each switch, I measured the voltage between the live and the earth. At the bathroom it was somewhere between 230 and 240V, so I reckon the earth there is ok.
At the WC, the voltage came out at 120V (which probably explains why I used to get a slight tingling when I ran my finger over the old metal switch!).
I can only conclude from that that, for some reason, the so-called earth wire is actually at 120V, thus giving a PD between live and "earth" of 120V.
Is there any other possible explanation? Where could the 120V for the earth be coming from?
Is the safest bet just to disconnect the "earth" in the switch and put a choc block on it?
Dave.
I have now finished converting all my unearthed metal light switches to plastic as talked about at //www.diynot.com/forums/viewtopic.php?p=827868
Interestingly, it turned out that for two of the rooms (the bathroom and downstairs WC) we actually did have a T&E cable serving the switch.
They also had metal back boxes as opposed to the plastic ones used elsewhere in the house. (When I say plastic, I am talking about some kind of old-fashioned plastic ones for use in brick walls rather than modern dry-lining ones).
At both the bathroom and the WC, the cable was fairly modern looking with a single piece of copper for each conductor, rather than the three-stranded silver-coloured conductors used in the rest of the rooms. At the WC switch the earth was bare and at the bathroom it was sheathed in plain green (so presumably not that modern)
On each switch, I measured the voltage between the live and the earth. At the bathroom it was somewhere between 230 and 240V, so I reckon the earth there is ok.
At the WC, the voltage came out at 120V (which probably explains why I used to get a slight tingling when I ran my finger over the old metal switch!).
I can only conclude from that that, for some reason, the so-called earth wire is actually at 120V, thus giving a PD between live and "earth" of 120V.
Is there any other possible explanation? Where could the 120V for the earth be coming from?
Is the safest bet just to disconnect the "earth" in the switch and put a choc block on it?
Dave.