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]

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!