Grounding and earthing advice for touch dimmer switch


Postby Rawthought » Thu May 05, 2016 10:17 pm

I'm paranoid...

I've just replaced a standard plastic switch with a metal fronted touch dimmer switch.

I replaced the 15mm back box with a deeper 45mm metal back box. I have wired up the switch as per the diagram. It's functioning as expected(ish)

It's fully earthed (I think). The Earth cable from the circuit is attached to the lug of the back box and a separate length of cable goes from the back box lug to the switch plate lug. The earth cable from the circuit was only just long enough to secure in the back box lug - so I secured it to the second earth wire with a touch of solder... Just for extra peace of mind.

My girlfriend text me at work saying she just received a shock/vibration when activating the switch... No spark, perhaps a buzz. She did give the sensor a push though when a light touch is all that is required to activate it.

I've had a test of the switch and received nothing from it - it's still behaving as I'd expect.

Does my grounding sound ok? I have a decent multimeter, is there an easy way of testing the front plate for grounding without unscrewing it?

Thanks - apologies if this is long-winded!
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Postby ericmark » Fri May 06, 2016 10:20 pm

In the main fixing screws connect to the earth. So on ohms range power off then you should be able to measure between a socket fixing screw and a light fixing screw and show less than 4 ohms. Limit is 7.67 but should not be anywhere near that limit.

The proper test meter uses a current of at least 200 mA so your multi-meter is not really good enough. But it is a good start. Not all screws are earthed some times only one of a pair in sockets is earthed. Same with switches screws not always earthed. So showing earthed does show OK but not showing earthed does not always mean there is a fault.
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