Electric Shock off a Light Switch

[Deleted member 105018]

Hi. Wondered if anyone can offer some insight. Basically this isn’t my area of work in general so hence the post.

I was asked today to oversee an investigation into a potential electric shock when someone switched a light on. The shock was described as a “massive” electric shock that supposedly blasted the victim against the adjacent door. Victim was ok afterwards with no lasting effects. Nobody seems to have seen the incident.

The commercial spark ran his tests. Basically the light is a double gang plastic switch (think cheap) on a plastic surface mount box. Inside the earth cables are terminated together but not to the box as you would expect with it being plastic.

There were no loose cable or damaged cables in the box. The guy testing ran an insulation resistance test from the light fitting with the switch in the ON position and found it to be fine. Zs measured at about 1.5ohms on a 6A MCB. RCD test tripping at 23ms at 1xI and at 7ms at 5xI. Similar results at 180. Ramp test showed RCD to trip at 24mA. Earth continuity belled back to dis board from every accessory and found to be fine.

The spark didn’t have an explanation. Neither do I. Settled on replacing the switch itself. Anything we’ve missed? Any advice welcome.

 

[45140]

Plastic accessory fitted to a plastic backbox with the earths jointed together but not to anything else so the screw wouldn't be earthed.

Yes quite right, my silly misreading of first posts. Thank you for pointing that out - I shall slink away with tail between legs

 

[ruston]

Yes quite right, my silly misreading of first posts. Thank you for pointing that out - I shall slink away with tail between legs

I think most of us are guilty of misreading posts from time to time ; don't worry about it . The main thing is you have a good sense of humour.

 

[Christian1981]

Hi. Wondered if anyone can offer some insight. Basically this isn’t my area of work in general so hence the post.

I was asked today to oversee an investigation into a potential electric shock when someone switched a light on. The shock was described as a “massive” electric shock that supposedly blasted the victim against the adjacent door. Victim was ok afterwards with no lasting effects. Nobody seems to have seen the incident.

The commercial spark ran his tests. Basically the light is a double gang plastic switch (think cheap) on a plastic surface mount box. Inside the earth cables are terminated together but not to the box as you would expect with it being plastic.

There were no loose cable or damaged cables in the box. The guy testing ran an insulation resistance test from the light fitting with the switch in the ON position and found it to be fine. Zs measured at about 1.5ohms on a 6A MCB. RCD test tripping at 23ms at 1xI and at 7ms at 5xI. Similar results at 180. Ramp test showed RCD to trip at 24mA. Earth continuity belled back to dis board from every accessory and found to be fine.

The spark didn’t have an explanation. Neither do I. Settled on replacing the switch itself. Anything we’ve missed? Any advice welcome.

Wet hands

 

[JOURNEYMAN]

Where was this? Why was a commercial sparky involved? Was the circuit in question in a domestic or commercial place? was the switch located in or next to a hostile environment, i.e. adjacent to a pub beer cellar or in a basement? Is it possible that there was a high humidity or condensation problem in the room or area in question?

 

[Toneyz]

i.e. adjacent to a pub beer cellar

Tel might have to be sent to investigate.

 

[EbolaSideRoom]

How is the switch wired?
I was called to a house once where the client claimed to be receiving an “electric shock” from a light switch.
Plastic plate on a steel knock out box, 2x cpc secured to box terminal, incoming live to L1, switched live to C, Neutral connection on L2. But old fashioned I thought...
The room was infrequently used, unheated and lightly damp, and this was on a cold winter evening.
I ran the usual tests (R1 + R2, IR, Zs, No RCD) and found nothing amiss.
It was getting on and I couldn’t find anything wrong, so I resolved with client to return in morning to continue the search....
...when I turned the light off and “BANG!!”.
I felt an significant discharge of energy very close to my fingers; it surprised, scared and “shocked” me, but I didn’t receive an electric shock.
I put it down to L/N arc through the switch as it turned off. Further examination revealed evidence of arcing in thenL1 & L2 terminals.
Replaced switch, removed N connection to insulated Wago style block, perceived shock disappeared.

How is that switch wired?

 

[brian.l.child]

Hi. Wondered if anyone can offer some insight. Basically this isn’t my area of work in general so hence the post.

I was asked today to oversee an investigation into a potential electric shock when someone switched a light on. The shock was described as a “massive” electric shock that supposedly blasted the victim against the adjacent door. Victim was ok afterwards with no lasting effects. Nobody seems to have seen the incident.

The commercial spark ran his tests. Basically the light is a double gang plastic switch (think cheap) on a plastic surface mount box. Inside the earth cables are terminated together but not to the box as you would expect with it being plastic.

There were no loose cable or damaged cables in the box. The guy testing ran an insulation resistance test from the light fitting with the switch in the ON position and found it to be fine. Zs measured at about 1.5ohms on a 6A MCB. RCD test tripping at 23ms at 1xI and at 7ms at 5xI. Similar results at 180. Ramp test showed RCD to trip at 24mA. Earth continuity belled back to dis board from every accessory and found to be fine.

The spark didn’t have an explanation. Neither do I. Settled on replacing the switch itself. Anything we’ve missed? Any advice welcome.

Just not possible the plastic compound used for light switches etc does not conduct electricity and depending on how much was paid wont even conduct static. Some of the cheap plastics have a nylon content which transmits static. They could be walking in nylon socks on a nylon based carpet. Bingo static.

 

[brian.l.child]

How is the switch wired?
I was called to a house once where the client claimed to be receiving an “electric shock” from a light switch.
Plastic plate on a steel knock out box, 2x cpc secured to box terminal, incoming live to L1, switched live to C, Neutral connection on L2. But old fashioned I thought...
The room was infrequently used, unheated and lightly damp, and this was on a cold winter evening.
I ran the usual tests (R1 + R2, IR, Zs, No RCD) and found nothing amiss.
It was getting on and I couldn’t find anything wrong, so I resolved with client to return in morning to continue the search....
...when I turned the light off and “BANG!!”.
I felt an significant discharge of energy very close to my fingers; it surprised, scared and “shocked” me, but I didn’t receive an electric shock.
I put it down to L/N arc through the switch as it turned off. Further examination revealed evidence of arcing in thenL1 & L2 terminals.
Replaced switch, removed N connection to insulated Wago style block, perceived shock disappeared.

How is that switch wired?

L1 L2 and common. Did it trip the RCD? The principal of L1 and L2 is that while one is on, then the other is off. It may only be significant if two switches were in use i.e. Upstairs and downstairs. L1 and L2 being both live would mean the light wouldn't switch off. The common is just the live once it has completed the circuit.

 

[Funky Gibbons]

I instantly thought of metal plated switch the line conducted had come away from the live terminal and was touching the metal plate, if this was the case I fail to see were this massive amount of current has come from and blown someone across the room, plus the plastic switch would not conduct electricity, I know anything’s posssible so would be interesting to hear what the experienced sparks have to say.

 

[Phillip]

There's a possibility that it's not the switch, the connecting cable in the wall could be damaged, making the wall live ( capacitance?) This would not trip or be picked up by test. The wall area could have been filled or plastered with a slightly conductive material, but insulated from the floor.

 

[EbolaSideRoom]

L1 L2 and common. Did it trip the RCD? The principal of L1 and L2 is that while one is on, then the other is off. It may only be significant if two switches were in use i.e. Upstairs and downstairs. L1 and L2 being both live would mean the light wouldn't switch off. The common is just the live once it has completed the circuit.

There was no RCD protection at the time of the fault I have described, if that is what you’re asking.
And it was (is) a single switch.

 

[Phillip]

Even with a RCD, the wall or whatever sourounding slightly conductive material could still charge up to a high voltage. Even its AC. More tests need to be done in my opinion.

 

[Funky Gibbons]

There's a possibility that it's not the switch, the connecting cable in the wall could be damaged, making the wall live ( capacitance?) This would not trip or be picked up by test. The wall area could have been filled or plastered with a slightly conductive material, but insulated from the floor.

Philip when you say capacitance, do you mean the the light had a capacitor inside the fitting charged up and in some way it was related to the shock they received am assuming this was a commercial install.

 

[Phillip]

There is capacitor, and capacitance, both are the same but physically different, not a subject to explain here. However there could be a capacitor in the light fitting, which could be the culprit. But it would still need the connection to something as the wall. But as I said earlier more tests need to be considered.

 

[Funky Gibbons]

There is capacitor, and capacitance, both are the same but physically different, not a subject to explain here. However there could be a capacitor in the light fitting, which could be the culprit. But it would still need the connection to something as the wall. But as I said earlier more tests need to be considered.

If there was a fitting with a capacitor your explanation on possible cause is the best explanation I’ve read, I agree with you we’d be summising with testing.