bulb blow causes circuit breaker to trip

[vet26]

another question (doing up an old house and lots of questions I'm afraid...!! :) )

We just got our house rewired.

The electricians put in a new circuit breaker (??) in the cellar where the electricity comes in. It comprises about sixteen switches (all used). They have placed the cellar and the 1st floor lights on the same switch (all are used).

Since they have fitted this, 2 bulbs have gone on the `1st floor. Each time, the switch in the basement has tripped and lights have gone in the cellar and the 1st floor. Bit of a pain in the butt since we need a torch to go down to the cellar to switch it, but is this normal behaviour? Should I worry about any of the electricians' wiring?

thanks for any replies

[Andrew Gabriel]

It can happen with MCB's. You could ask the electricians to change the lighting circuits for 5A BS1361 cartridge fuses, which will stop this in most cases. In some cases, changing the MCB from a Type B to a Type C might help, but in other cases it doesn't.

Alternatively, change over to low energy lamps, which don't cause this.

[John Rumm]

The other easy thing to do is to have a battery maintained emergency light (about £30) installed near the consumer unit, and have it powered from the same circuit that feeds the lights in the room the CU is in.

That way when you do loose the circuit the light comes on and you can see to reset it.

[The Natural Philosopher]

Sadly it is fairly normal - here anyway.

Candle bulbs are the worst offenders.

[jethro_uk]

I noticed this when I replaced our CU. I believe the reason it happens is that as a bulb blows, there is a split second when the filament breaks, and an arc appears across it. IIRC, the resistance of an arc is very low (milliohms ?) which causes the current drawn to appear almost infinite - certainly greater than the 16A of the MCB - hence the trip. This doesn't happen with fuses because the duration of the arc is so short that a normal fuse can't react in time. However the MCB can react much quicker.

I vaguely recall (maybe from uk.d-i-y, a google might help) that there are "slow blow" MCBs for just this purpose, BICBW

[Ian Stirling]

As others have said...

However, if you use energy saving lights, they don't usually do this.

[Owain]

Especially as it's in a cellar.

Owain

[Guy King]

The message from [e-mail] contains these words:

Happens all the time. As the filament breaks it causes an arc inside the bulb, which spreads along the remains of the filament to the wires that carry the current up to it. Arcs have very low resistances - far lower than a working bulb and the surge in current pops the circuit breaker. Most bulbs now have an internal fuse - but it still happens.

[Helen Deborah Vecht]

The Natural Philosopher typed

The mini-globes in my hall do it a lot too.

[Malcolm Race]

Tried 'C' type MCBs - doesn't seem to make much difference

Malcolm

[The Natural Philosopher]

Yus, I had one of those do mine in again as well.