Short circuit did not blow any fuses

Hi

I'm new to the forum and seeking advice.

I had an issue tonight of a short circuit on a 'kettle' type lead (the type with a clover leaf shape connecting a laptop psu).

The Mrs shouted up in a panic that something was burning, I rush downstairs and we find the cable smoking away, she lifted the psu off the carpet and there was a couple of flashes and popping etc and I turned it off at the wall, the whole episode lasted maybe about 30 seconds.

The cable nearest the clover leaf end had split open and shorted out and melted, the neutral cable seems to have melted away, the earth is exposed and it looks like the live was not shorted but unsure. I'm guessing that the cable was initially damaged by the sofa as it's an electrical reciner type and quite possibly trapped the cable between it and the floor a few times.

I checked the fuse in the plug, 13A and did not blow, neither did the ring main MCB. The socket it's plugged into is no more than about a couple of metres away from the consumer unit.

The wiring and consumer unit is approx 12 years old now as I rewired it when we moved in, seperate ring mains for upstairs and downstairs on their own MCB's. I did qualify as a sparks 15-20 years ago but didnt contunue past the apprenticeship as I changed trades to a slightly different field, so am not up to date on the regs and rusty on the theory side of things, but consider myself competent enough for DIY still.

So my question is: Why no trip? Ok the 13A fuse was too high for the device - will get a load of 5a's tomorrow and check all my computer kit etc and change them all. Should not the MCB have tripped or would it have taken longer? I'm quite concerned it was crackling away and not tripping anything. I'm wondering if it was only the earth and neutral shorting out but would that have caused the fireworks? Maybe the PSU itself added to the problem if developing a fault?

Any advice appreciated, will open up the socket tommorow and double check connections and voltages, but getting a bit concerned.

Cheers

Rich

Depends on which conductors the short was between (if it was a short at all or just some components burning out)

If your rewire did not consist of any testing then you would not know if your earth fault paths were adequate which could mean insufficient disconnection times.

r1000 said:

I'm new to the forum and seeking advice.
~~~~~
will get a load of 5a's tomorrow and check all my computer kit etc and change them all.

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Seems you have given yourself the best advice

r1000 said:

the neutral cable seems to have melted away,
I checked the fuse in the plug, 13A and did not blow, neither did the ring main MCB.

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The thin wires in the lead can easily melt or just glow red hot when less than 13 amps flows through them.

But still check your wiring. Lack of RCD trip strongly suggests there is a problem with the earth to that socket if there was an earth wire involved in the arcing lead.

Thanks for the replies

just to confirm, there are no rcd's in the circuit, just an mcb.

i'm hoping it's just a case of the cable being fused too highly.

I wonder if it's worth getting a professional inspection. i have a multi meter so could check for correct voltages across the cores at the socket and for presence of earth, but not much more.

any other comments welcome

thanks

Rich

The cold inrush currents on power-up of laptop power suplies and other SMPSs can give plug top fuses a very hard time, often popping apparently correctly rated fuses. I have witnessed quite a few 40 Watt SMPSs popping 5 Amp plug top fuses on power-up.

So it is not unusual for 'oversized' fuses to be fitted The power supplies themselves often have the the correct rating fuses, but incorporating a time delay to overcome the cold inrush problem. Such fuses are not available for 13 Amp plugs, so there is little alternative to fitting over-rated standard fuses.

If 5, 7 and 10 Amp fuses were more commonly available the problem may be reduced, but they may still not afford adequate protection for the power lead.

r1000 said:

just to confirm, there are no rcd's in the circuit, just an mcb.

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r1000 said:

consider myself competent enough for DIY still.

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