Discuss Mains electric shock from plastic light switch - no fault found by electrician - what next? in the UK Electrical Forum area at ElectriciansForums.net

jimster99. Good evening Sir.

We are a nosy crowd and really like to know about how problems which have been presented are resolved especially when we have 'skin in the game'.

I noticed that the light fitting has been replaced some time which may be significant. We will not ask by whom. What we really want to know is whether this problem has been first explained and second resolved so that it is safe for all. Unless one understands how you received the shock ie explained by careful investigation it is uncertain whether it could happen again.
 
jimster99. Good evening Sir.

We are a nosy crowd and really like to know about how problems which have been presented are resolved especially when we have 'skin in the game'.

I noticed that the light fitting has been replaced some time which may be significant. We will not ask by whom. What we really want to know is whether this problem has been first explained and second resolved so that it is safe for all. Unless one understands how you received the shock ie explained by careful investigation it is uncertain whether it could happen again.
Hello Marconi! Thanks for the reply (and for your earlier very helpful comment that damp socks = no static!) and don't worry, I have not forgotten about this - I am very keen to avoid future shocks! :)

The light itself had been replaced by somebody before we moved into the property. We don't know who!

The outstanding points appear to be:

(i) checking the RCBO: why didn't it trip? I suspect because I got less than the 30ma trip level. It's worth noting that we had a faulty metal electric kettle a few months ago that DID trip the RCBO a few times, although I suppose it could have been a short circuit tripping the fuse rather than a voltage leak. But this should be checked (which requires taking the front of the RCBO box off).

(ii) Is the internal wiring of the LED itself correct? You asked for a photo of the inside of the light and I will do this when I get a moment (hopefully today). I have the VED screwdrivers ready to go!

(iii) should the internal lugs of the switch be bent back to avoid any future risks of electric shocks? EDIT - yes - and I will do this myself (since the electrician didn't) after cutting the power to the entire property.

(iv) check earth continuity back to board.

(v) The earthing resistance needs to be checked which requires a fault loop impedance test. Is this the same thing as (iv)?

(vi) an insulation test needs to be carried out on the circuit (rather than just the switch) which requires taking the front cover off the RCBO.

Odd. Carrying out an insulation test on the circuit (as distinct from the switch) requires taking the front off the board to disconnect the neutral. In which case an RCD test can be done at the same time, taking less than a minute. If he did not test the circuit insulation and did not open the board, then it is still possible to do the RCD test from the switch position albeit with a bit of legwork to visit the board a few times to reset the RCD.
Hmm, he only checked the switch insulation, not the circuit insulation. Shall i get him to come back and check the circuit as well? He didn't seem to think it was a necessary check but better safe than sorry I think!

There's a remote possibility that it's the floor that is 'live' as a result of a nearby fault, and that the shock came from touching correctly earthed metal in the switch.
I hope this can be ruled out because of the fact that the light itself was intermittlently pulsing when switched off shortly before the shock - too much of a coincidence otherwise.
 
Last edited:
OP…. My suggestion of bending the top and bottom lugs off aren’t a regulation or anything.
Some makes of switches have terminals very close… and are only a problem if you’re taking a switch off the wall without isolating first.. very easy to brush against, then bang. Or click… if it’s on an rcd.

Does your rcd work at all by using the test button?
If it’s been going off with a big enough fault, it maybe not working properly.

Your electrician should have checked this as a matter of course with the right equipment.
It would tell him how fast it trips… has to be under 40ms, and how sensitive it is.
 
If you feel confident and only if you do please turn off the main switches on your consumer unit and all the circuit breakers. Then take the cover off the lamp and then take the lid off the white terminal box I have pointed to with green arrows. Take a photo of the terminal block inside and post it.
I've checked inside the chocolate box, I think it looks like the wires are correctly connected (especially the earth!) Photos attached as requested. Thanks!! :)

1655224312281.JPEG


1655224313473.JPEG


1655224320015.JPEG


1655224322022.JPEG
 
Oh well… the light fitting has been connected properly. It did look like there was a swapped over conductor from the earlier pictures when it still had the lid on the connector.

Make sure you put that lid back on
 
There's something a bit odd about that set up. Live and neutral come from one direction, cable sheath barely entering the fitting, and the cpc comes from a different direction.
 
There's something a bit odd about that set up. Live and neutral come from one direction, cable sheath barely entering the fitting, and the cpc comes from a different direction.

I think L, N and E all come in through the grommet at the bottom side of the connector block don't they?
 
Now I would take the fitting down and examine the wiring underneath.

Jimster99 - if you feel confident first turn off both red main switches and all the circuit breakers and then remove the fitting securing screws while taking the weight of the fitting. Then take a photo of what you see of the wiring above the fitting especially of any connectors. Then carefully put everything back in place, turn on mains switches and the circuit breakers.
 

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