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.

 

[Andy78]

What material is the carpet made of ?

 

[Deleted member 105018]

It’s concrete. I can’t see it being static. Especially considering the box isn’t earthed with it being a surface mount plastic box.

 

[DPG]

Difficult to see how such a massive shock could be obtained in those circumstances you describe. It's not somebody 'trYong it on' is it? Have they mentioned compensation ?

 

[Squid]

Did the person that received the electric shock justexti a swimming pool and was dripping with water?

 

[Deleted member 105018]

No the person was totally dry. It’s a strange one. No the person hasn’t mentioned combo but I am inclined to believe that the story may be a little fishy.

 

[MFS Electrical]

Was the switch arcing and possibly frightened someone?

 

[Deleted member 105018]

I wondered that myself. The person is insisting that they received a shock. It’s always a little concerning when you don’t find anything wrong.

 

[Deleted member 105018]

I think I’ll just present my findings and leave it at that. Just wanted to be sure I hadn’t missed something in your opinions.

 

[ruston]

Maybe has Cervical Spondylosis in the neck, lifting the arm can cause severe pain in the neck and tingling in the arm similar to a mild shock.
If they have not had it before this can be quite alarming.
Other than that I am with @DPG

 

[Deleted member 105018]

Thanks folks. Appreciate the input.

 

[Nigel]

He is talking rubbish. Not sure how anyone can get a shock from plastic.

 

[Toneyz]

What is the switch switching I know sometimes you can see the arcing in the small gap when making and opening the switch contacts?

 

[Squid]

Replace the switch at least it looks like you have done a pre emptive fix.

 

[Edtwozeronine]

A friend of mine recently got a shock from the metal cassing of an old 12v transformer he was tinkering with. I'm quite surprised he's not dead! 0_o

 

[Andy78]

I was thrown across the room when I touched that plastic switch.

No. No you weren't.

 

[Deleted member 105018]

Haha. Trying to convince someone there’s nothing wrong is harder than you’d think!!

 

[littlespark]

Was there any fluffy carpet in the room the person walked through to get to the concrete floored room?

The person may have generated enough static but it didn’t Earth until they touched the switch, or more exactly, the metal screws.
However, OP said the CPCs were not connected to the metal back box, so there would be no path back to earth.

 

[Deleted member 105018]

Yes that’s correct. The CPC were just terminated together in some terminal block. The back box was actually a plastic surface mount box which of course don’t need an earth connection. Therefore as you say any static would not have discharged even if the person touched the screws.

 

[Dave OCD]

If it's a cheap switch it may have been a small arc which 'escaped', especially with flourescent or other discharge lighting with capacitors in the circuit. But even then it's highly unlikely that someone would be thrown across the room.