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.

 

[a-z electrics]

If cause is static electricity then you wouldn't necessarily need an earthed surface to be touched to allow discharge. In fact there would be a bigger discharge if there was a small insulative air gap . Its possible if the cpc was a (few) mm away from a fascia screw tip then a large build up of static eventually discharged across. I don't think you would necessarily see a visible burn Mark.
Some people are particularly susceptible to static build up just because of their physical chemistry. And I'm not saying they don't wash!