Investigated an electric shock today.

GBDamo · Sep 13, 2019

Was called out to a site where an employee has recieved an electric shock when turning on a light.

When I isolated and removed the switch the cause was immediately apparent.

[ElectriciansForums.net] Investigated an electric shock today.

It was a metal surface box and mettal clad switch, the back box had been drilled through the back for a 20mm conduit but never used, favouring a top entry using condit.

Basically the rear entry hole had left a nasty burr which over 30ish years has slowly cut into the line conductor until yeasterday when someone operated the switch and wallop.

The guy had a lightly singed finger and attended hopital for a check up but was otherwise ok.

Fortunately the circuit had been put on an RCBO due to an addition, although not necessary at the time.

Amazing how such an issue can sit there for so long before zapping someone.

davesparks · Sep 13, 2019

Was the box not earthed?

westward10 · Sep 13, 2019

Looks like is was to me shows clear signs of fault current.

GBDamo · Sep 13, 2019

davesparks said:
Was the box not earthed?

Yes, by twisting the cpcs round on of the fixing screws.
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I've pictures of how it wss installed but cannot access them, just kept the box for my personal hall of shame.

Dustydazzler · Sep 13, 2019

I wonder if the person who got the belt happened as they put pressure on the switch pushed it back just enough so the live conductor got squashed against the sharp edge and bang.

Lucien Nunes · Sep 13, 2019

So the question is, what was the shock voltage and duration? The box must have been reasonably well earthed to produce a splash like that, in which case the RCBO should have responded quickly. And a short duration shock of modest contact voltage, although nasty for a moment and a potential trigger of a cardiac event, is unlikely to cause a burn.

davesparks · Sep 13, 2019

Did the finger actually get burned, or did it get a bit of a black mark on it?

Is that black mark definately the result of this incident or could it be left from an older incident? I don't think I've seen a black mark like that on a circuit with 30mA rcd protection before, they usually disconnect long before enough current flows to cause that.

GBDamo · Sep 13, 2019

Dustydazzler said:
I wonder if the person who got the belt happened as they put pressure on the switch pushed it back just enough so the live conductor got squashed against the sharp edge and bang.

From what was said that's exactly what happened.

Makes yoi wonder how many times that switch has been pressed in it's lifetime.

Grant1987 · Sep 13, 2019

GBDamo said:
From what was said that's exactly what happened.

Makes yoi wonder how many times that switch has been pressed in it's lifetime.

Has the person concerned ever had an electric shock before? I’m wondering if he was just shocked by the flash and bang thats enough to scare you but as long as he’s fine and well that’s the main thing lethal industry we are in and hope it doesn’t scare him off.

GBDamo · Sep 14, 2019

Grant1987 said:
Has the person concerned ever had an electric shock before? I’m wondering if he was just shocked by the flash and bang thats enough to scare you but as long as he’s fine and well that’s the main thing lethal industry we are in and hope it doesn’t scare him off.

No, i think he got a propper crack, he not a spark but an employee at the business concerned.
He certainly is a bit wary of switches now.