Customer managed to take out company head!

[sparkybird]

Had a call last week from a customer who looks after some rental flats. Tenant had reported problem with cooker circuit tripping plug in mcb. he went round to 'have a look and a fiddle'

Reset mcb - it tripped
Reset mcb- it tripped
Reset mcb and HELD IT UP
I imagine a bit of swearing, maybe a flash and then loss of all power.

Idiot had managed to blow the main fuse (60A)!

Cue phone call to me...

 

[RF Lighting]

What did you do?

I'd voltstick the cutout and call the DNO.

Oh and charge for them for the callout

 

[sparkybird]

Well, rightly or wrongly, I disconnected the circuit, ran a systems tests on the rest (1 power and 1 lighting circuit - TINY flat!) and used the 60A spare that I always carry to give the tenant back some power. Am back this week to sort out fault and upgrade DB

SB

 

[RF Lighting]

You'll go to hell for that.

 

[sparkybird]

Well, here's hoping!

 

[hairyben]

What brand of plug-in-mcb was it? I thought the things were fail safe, ie the lever will re-set the mechanism but not prevent it re-tripping- the mechanism will break the circuit and the level will just spring back when you let it go.

otherwise kitchen fitters would just sticky tape them on.

 

[sparkybird]

it was a wylex 69808 b - you know the old rewireable replacement ones - 30A

I guess it is possible to hold it up - wouldn't like to have been his finger at that point! Mind you the whole install was rather old, so it might have been faulty?

 

[Adam_151]

What brand of plug-in-mcb was it? I thought the things were fail safe, ie the lever will re-set the mechanism but not prevent it re-tripping- the mechanism will break the circuit and the level will just spring back when you let it go.

Chances are that it never actually failed, just that after a few goes, the fuse was nicely warmed up to give it enough of a headstart in the discrimination race. An old wylex plug in breaker is probably not as fast as a modern one either.

That said... I'm not sure I'd reuse the breaker either!

 

[RF Lighting]

IIRC those plug in MCBs don't have an especially high breaking capacity.

The repeated quick resets might have killed something internal, or even drawn an arc across the switching contacts. I think adams theory is probably most likely though.