main fuse tripped

[600rob]

Bought three flush mounted sockets to replace the stock white plastic ones in a room that im decorating.

Fitted them a couple of weeks ago and all working fine. No issues.

Last night was decorating and loosened the fixing screws just so the sockets could be displaced and allow me to paint around thw socket.
On moving one of the sockets probably no more than 10mm a loud pop and lots of sparks came from behind the socket.
The circuit the sockets was on tripped and also the main entry fuse in the meter box tripped.

On inspection the socket live terminal is quite charred. All wires however were firmly clamped in place.
There are no scorch marks on any of the wires
I hadn't started painting and all tools were clear of the socket.

Other that a faulty socket which I doubt as it was working fine for a couple of weeks what else could have caused this?

 

[securespark]

There must have been a short circuit.

Did you put your screwdriver behind the socket?

Is there a charring on the earth bar anywhere?

 

[Spark123]

Moral of the story, isolate before working on any electrical circuit.

 

[600rob]

Definitely no tools or screw drivers any where near the socket or back box.

There shuldnt be any but
I will double check for any exposed wires tonight.

Lesson learnt though... will take the time to isolate in future even if its just for a 'quick' job

 

[Spark123]

If it was a metal back box it may be just the live screw has come into contact with it.

 

[ban-all-sheds]

the main entry fuse in the meter box tripped

I find that hard to believe.

1. Fuses don't trip, they rupture, or "blow".
2. The main fuse can only be replaced by the DNO - did they attend today?
3. The protective device in your for that circuit really should have operated before the service fuse went.

 

[PBC_1966]

Perhaps it's a main RCD fitted in the meter box which tripped?

 

[Spark123]

Or an ELCB (old voltage flavour)

 

[Echo the husky]

Or an ELCB (old voltage flavour)

Ooh I removed a 3 phase version of one of those last week.

Have you replaced the socket with a new one yet?

Sometimes old cutout fuses can blow when there is a fault. I went to a call out where a very old electric heater had gone bang when it was switched on, and blew the cutout fuse. I still have the old heater it works fine and I could find no signs of any faults, either current or previous...

 

[radioredcat]

My wife switched a light on and it tripped the MCB and on investigation I found a single screw for the back box at an angle with a sharp edge this had penetrated the insulation on the live wire so had to countersink the hole in the back box so it fits nearly flush fortunately there was enough wire to cut the bad bit out.

Andy

 

[Iggifer]

My wife switched a light on and it tripped the MCB and on investigation I found a single screw for the back box at an angle with a sharp edge this had penetrated the insulation on the live wire so had to countersink the hole in the back box so it fits nearly flush fortunately there was enough wire to cut the bad bit out.

Andy

Using pan head screws avoids this problem. Can't say I've ever needed to countersink a knockout box to get the screw flat enough. Even with a countersunk screw head.

 

[securespark]

Black japs.

 

[radioredcat]

My wife switched a light on and it tripped the MCB and on investigation I found a single screw for the back box at an angle with a sharp edge this had penetrated the insulation on the live wire so had to countersink the hole in the back box so it fits nearly flush fortunately there was enough wire to cut the bad bit out.

Andy

Using pan head screws avoids this problem. Can't say I've ever needed to countersink a knockout box to get the screw flat enough. Even with a countersunk screw head.

I had to use what I had to hand but all the switches are the same so I will get some of those screws.

Andy

 

[Iggifer]

Did you do them up by hand? if you use a drill/impact driver you can just force them in so far the box bends and you don't need to bother

(that's half serious - if you do them up tight enough it's not an issue, just don't over tighten them)

 

[PBC_1966]

Using countersunk screw heads with a metal back box seems to be all too common, but it's just not the proper type of screw for the application.