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Electrical
Switch with Metal plate has Earth connection but showing high voltage
Anonymous user 1 March 2024 - 2.59 PM
Hi,
A year or so ago I had a DEICR done on my property and the electrician ended up fixing a bunch of things such as supplying a new fuse box, adding earthing to a lot of switches/pendant lights that had no earthing etc.
When fitting a new pendant last week and replacing the switch with a metal plate, I noticed that the Voltage Tester was signalling quite high current at the metal plate. The switch has an earth connection and so does the pendant (which doesn't seem to trigger any abnormal voltage flowing through it).
I went across the whole house and this is the only switch (or socket, all in metal plates) that triggers the voltage tester.
I've replaced the switch and the same issue lingers. The back box is made of plastic. What is the cause for this? Would it be the Earth cable being having some kind of fault? If so, wouldn't the pendant fitting also expected to have an issue?
Thanks
Are you a tradesperson and able to answer this question?
What is the voltage reading? Sometimes when you get a half normal voltage (say 120V or thereabouts) its because there is no cpc continuity at the switch. That particular switch could have been missed during remedials. If you test across live and earth (cpc) you should get 240V. If you only get half that then thats the reason. If you are getting a voltage on the plate that is also indicative of no cpc connection even though the wire may be present.
Answered25 October 2022
9
Anonymous user
It might be just induction voltage from dimmer or transformers/drivers. Induction voltage means nothing. It won’t trip the RCD or do anything to you.
Like other people have said that switch plate needs to be opened and checked that earth is actually connected. Even if connected you might still get some induction voltage. There is no simple answers unfortunately. Someone needs to have a look at it and possibly even check if there is current flow but I would be surprised if there was any.
Any touch voltage that you get at the switch is likely to be due to either a missing or poor earth connection. If this is the only switch that you are getting this at then it's likely to be a localised earth to the switch thats gone.
You shouldn't have any more than 50v touch voltage (i.e. when you touch the front of the switch) at any point in the property. My advice would be to change the switch for a plastic (double insulated switch) in the short term and get someone to take a R2 value (earth/CPC continuity) for you from the consumer unit to the CPC in the light switch to see if it is actually connected. If it's not then thats your answer
