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.

 

[Strima]

If the shock was sufficient enough to throw them a reasonable distance then there would be signs of shock injury to the body part that touched the switch and also where the current exited the body.

And burns on fingers, soles of feet etc?

Sound like someone is talking bowlicks to me.

 

[Rpa07]

You need to tell them that an ECG must be carried out at A+E and the wait may be up to 2 hours even to be seen.
This is because they may have suffered a disruption in their cardiac rhythm and could die any moment.
They may come clean and admit they are a thespian! Not that that is a bad thing!

 

[littlespark]

Indeed.
An actual electric shock so severe would leave marks on the skin, and no doubt bruises from where the person landed.

The RCD protecting the circuit tested ok, plastic switch... connections fine.

I therefore conclude Dr Watson that there is no chance that someone could receive a shock from said apparatus.

Now if it was a metal backbox, AND there was a loose wire touching the metal, AND the backbox wasn’t earthed AND there was no RCD protection THEN I would think a shock would be probable

 

[Deleted member 9648]

Some time back I started a thread on people who on finding out you are a sparks invariably have a story of how they were 'thrown across the room'.
This is one of the better ones I've heard, blasted against the door !!! That's an absolute belter (pun intended).Since that thread I've taken to telling the story tellers they are talking complete sheeit.
I suspect there may be a claim for COM-PEN-SAY-SHUN involved here.is it a rental?
edit....I see other cynics have also mentioned the C word!

 

[MJPD29]

Story has been exaggerated and person possibly looking for a claim? Seems unlikely that this would happen with a plastic switch

 

[Toneyz]

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.

This was the point that I was alluding to in my question of the load it was switching and seeing a small arc in the gap of the switch possibility if worn or poor contact the arc may be more significant.

 

[Strima]

This was the point that I was alluding to in my question of the load it was switching and seeing a small arc in the gap of the switch possibility if worn or poor contact the arc may be more significant.

There would definitively be burn injuries on the individuals finger.

 

[Toneyz]

There would definitively be burn injuries on the individuals finger.

What friction burns from the air as they were thrown across the room.

 

[Chris1234]

I get the occasional muscle spasm in my hands, it feels so much like an electric shock that I have to check around to see if anything is live that I could have touched.
Other people have seen this happen and assume I’ve got a shock.


Also I worked with someone many years ago who seemed to get electric shocks from everything, although she did always wear a wool jumper. She’s also long term sick now!

 

[Silly Sausage]

I get the occasional muscle spasm in my hands, it feels so much like an electric shock that I have to check around to see if anything is live that I could have touched.

I've occasionally experienced similar.
I'm sitting watching TV or lying in bed whatever, and completely out of the blue, it's like someone has zapped me, head to toe, with the mains. Then it's gone.

Weird!

 

[ferg]

I've been reliably informed by a customer of mine that it's probably due to an excess of electricity in the body.

I gave up in the end.

 

[ruston]

I get the occasional muscle spasm in my hands, it feels so much like an electric shock that I have to check around to see if anything is live that I could have touched.
Other people have seen this happen and assume I’ve got a shock.


Also I worked with someone many years ago who seemed to get electric shocks from everything, although she did always wear a wool jumper. She’s also long term sick now!

I get that too . I have degeneration of the spine , but my neck suffers the most . When the nerve traps in the neck it is just like an electric shock.
It affects the arms too. You should go for a check up.

 

[Chris1234]

Even this shock only “f**king hurt”, no mention of being thrown backwards or anything.
I believe the second time he touched it was a similar experience also!

 

[ruston]

Edit.
Duplicate post.


















































































I get that too . I have degeneration of the spine , but my neck suffers the most . When the nerve traps in the neck it is just like an electric shock.
It affects the arms too. You should go for a check up.

 

[static zap]

I've been reliably informed by a customer of mine that it's probably due to an excess of electricity in the body. I gave up in the end.

..ask if they always killed digital watches ...!

----More about situation (Rainy or Dry day)....

Were they on their own , did they have to open any doors(using clothing rather than hands) ,pushing a trolley , or dragging plastic sheeting behind them.
..Had they recently got out of a car -Chauffeur assisted ?..
Any signs of a source of water .
(Does switch protrude to be used as a coat hanger on a wet day)

.. Maybe get replacement with cap covers over screws ..!

...returning to trolley--may be off it..

 

[dmxtothemax]

1.5 M ohms sounds big !
But it is not
I would expect much higher on plastic

 

[telectrix]

brain to feet elctrical impuse, as in get up and do summat.

I've occasionally experienced similar.
I'm sitting watching TV or lying in bed whatever, and completely out of the blue, it's like someone has zapped me, head to toe, with the mains. Then it's gone.

Weird!

that just happens on the rare occasions when the brain decides to shift into gear. .

 

[Intoelectrics]

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.

Me thinks somebody has been watching too much sci-fi! Or Judge Judy!

 

[richy3333]

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

You've not seen my wife's credit card bills then

 

[ChrisElectrical88]

Didnt happen did it, from what you have explained, i would happily go and disinfect and lick the switch to prove he was lying.

 

[BroadReach]

If you discount the throwing across the room bit, I have seen this in the past:

Electric shock on a plastic rocker switch. On further investigation I got 80-100V by putting a multimeter probe on the gap between the toggle and faceplate - to earth. On closer inspection this was full of dark black detritus.

This was in a kitchen and I imagine the switch being wiped with a dirty dishcloth over the years........

 

[Silly Sausage]

brain to feet elctrical impuse, as in get up and do summat.
that just happens on the rare occasions when the brain decides to shift into gear. .

You calling me lazy?

 

[DefyG]

Sounds like a job my mate Nige did, the biggest shock was that it actually worked!

 

[45140]

I work with MV and HV electrical. No-one gets "thrown" by an electric shock irrespective of the voltage.

A person creating a dead short against say 25kV can stay in contact with the equipment until recovered. I can see a person being pushed back where there is vapour in the air, which is converted to an expanding gas when the electric arc is created, but in those cases there would be hot vapour as opposed to electrical burns.

Had there been a high volume nylon carpet and insulating shoes, then quite a head of static electricity could build up in the body, and the discharge route would be via the metal screw securing the faceplate. If there was some sort of resultant effect on the muscles then the person could have suffered a spasm. Personally I think this is what has happened as the static discharge through the fingers would make a loud crack as well as being painful. Seriously dispute that this is a circuit-related electric shock incident.

 

[Strima]

Had there been a high volume nylon carpet and insulating shoes, then quite a head of static electricity could build up in the body, and the discharge route would be via the metal screw securing the faceplate. If there was some sort of resultant effect on the muscles then the person could have suffered a spasm. Personally I think this is what has happened as the static discharge through the fingers would make a loud crack as well as being painful. Seriously dispute that this is a circuit-related electric shock incident.

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

 

[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.