Mains electric shock from plastic light switch - no fault found by electrician - what next?

[Sapper]

I may go against the grain here but I just don't like the LAP brand - personal experience includes short life spans caused by burnt out drivers and poor terminals. Even if there is not a wiring problem I'd personally get it replaced with something better.
The earthing problem still takes priority though.

 

[LukeD]

LAP and BG are now well and truly on my avoid list

 

[littlespark]

If you search through the forums, you’ll find stories of not so good LAP or BG products, but usually followed by a positive example of another product by the same.

It’s like a lot of other things… sometimes you get a good design, sometimes not.

I really don’t think this threads issues are down to the choice of fitting, but either installation mistake, or breakdown of much older equipment..

 

[SJD]

I may go against the grain here but I just don't like the LAP brand ...

While I agree about not liking LAP, I thought the new switch looked like MK Logic ... ?

 

[jimster99]

T

Good getting a new switch, but did he bend back the unused screw lugs?

Was there any further testing done? There is still the issue that you got a shock, and the RCD didn’t trip.
This is far from resolved.

Thanks for the follow up!! He did not bend the unused screw lugs back, should I do this myself? I feel confident that I can safely disconnect the circuit via the RCD/fuse box prior to doing this. He did do a 500v insulation test (as you suggested!) and found no problems. It was about a 1 hour visit in total. He didn't check the RCD (said it would take too long and require dismantling the box...).

I see there are some additional comments including to dismantle the light (which I feel confident enough to do). I really appreciate the feedback on this very friendly and helpful forum. I will take a look at those later today and post back!

 

[jimster99]

Neither you nor the investigating electrician found any evidence of moisture?

Re: moisture, there was no sign of moisture inside the switch found by me or the electrician. There was also no sign of arcing damage.

Although now I think about it I do remember seeing a few droplets on the wall high above the switch when the shock happened, which I remember thinking was odd because I don't know where they could have came from - possibly after I washed my hands I might have shaken them before touching the switch leaving drops on the wall and the moisture on my hands itself was sufficient to conduct? Although it's outside the bathroom there's no possible way water could splash off the shower or sink and into the switch because of the angles. The switch is in a cavity wall insulation and we did also have a heavy thunderstorm over the weekend in London so I wondered whether perhaps some moisture might possibly have come in through the roof (although seems unlikely given we are on the first of four floors). I have never seen any other signs of damp or water leaks.

The second possibility is static from the carpet you stood on.I know you have ruled it out but static can be very unpleasant.Experiencing it while wearing damp socks and having damp hands can can be extremely unpleasant

Re: the possiblity of it being static, I am certain it was an AC mains electric shock. I have had a mains shock once years ago from (ironically) the screw on a faulty light switch on a bathroom in a hotel in the middle east, and it has a distinctive throbbing feel and causes throbbing muscle contractions down your arm into your body and is very frightening/unpleasant/painful. This was the same. Static is (in my experience) a much sharper single shock with no throbbing and that only hurts at the contact point - I've played with e.g. a van de graff generator so I do know what a bad static shock feels like I would love for it to be a simple static shock explanation but I just don't think it is.

My first step would be to have your earthing checked.A high earth resistance will cause shocks to be felt in any earthed metalwork when certain appliances or plugged in.A fault loop impedance test will quickly establish this.

Thanks! I will check if the electrician did this test and if not will arrange to have it done (I assume I can't do it myself with a simple consumer multimeter unit)?

 

[Lucien Nunes]

. He did do a 500v insulation test (as you suggested!) and found no problems. It was about a 1 hour visit in total. He didn't check the RCD (said it would take too long and require dismantling the box...).

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.

 

[marconi]

What you experienced was not due to static electricity because you were wearing slightly damp socks which would have discharged you.

 

[LastManOnline]

What you experienced was not due to static electricity because you were wearing slightly damp socks which would have discharged you.

Good point.That effectively rules static out .I personally would be very confident that "dampness" is also not the issue so looking forward to hearing what results from testing the earthing.

 

[brianmoooore]

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.

 

[LastManOnline]

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.

Remote.But certainly a possibility.If the installation earthing proves to be good than it could even become a probability.Especially with static now ruled out

 

[marconi]

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]

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.

 

[littlespark]

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.

 

[jimster99]

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!!

 

[littlespark]

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

 

[brianmoooore]

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.

 

[DPG]

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?

 

[brianmoooore]

Yes, the brown and blue are going to the driver, and the incoming cable is the white wires. HR sleeving?
Cable sheath still doesn't come into the fitting.

 

[marconi]

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.