Blown bulb tripping circuit but not mcb ???

shadybrady · 23 Jan 2008

My mum and dads house has a new consumer unit but at the moment still the old wiring (replacing one circuit at a time).

Weird thing is, that if a bulb blows, the circuit trips out but the mcb doesn't, the switch still remains on??

Any ideas - could it be that the old wiring isn't supplying 'enough' of an overload fault to actuate the mcb switch??

JohnD · 23 Jan 2008

I don't understand what you mean when you say "the circuit trips out but the mcb doesn't,"

What is the thing that trips? What is written on it (all letters and numbers please)

What is the thing that doesn't trip? What is written on it (all letters and numbers please)

ban-all-sheds · 23 Jan 2008

Aren't some MCBs made so that when they trip they don't move the lever, which then needs to be flicked to the off position before it can be reset? (the idea being to stop the operation of the MCB being prevented by external mechanical interference)

JohnD · 23 Jan 2008

that would be very odd. there are RCDs that only move half-way, but IIRC modern MCBs have to have a positive visible indication of contact position. Maybe they have a red/green indicator in a window?

shadybrady · 23 Jan 2008

Basically when the bulb blew all the lights in the circuit went off, but on checking the mcb it was still in the 'on' position but none of the lights worked and there was no power to the circuit.

I then went and moved the mcb to off position then back on, and all the lights came back on - essentially the circuit tripped but the mcb switch didn't move to the 'off' position.

JohnD · 23 Jan 2008

time for a new MCB

daytona · 23 Jan 2008

shadybrady said:
Basically when the bulb blew all the lights in the circuit went off, but on checking the mcb it was still in the 'on' position but none of the lights worked and there was no power to the circuit.

I then went and moved the mcb to off position then back on, and all the lights came back on - essentially the circuit tripped but the mcb switch didn't move to the 'off' position.

what make is the mcb?
are you sure it didnt drop down a bit?

shadybrady · 23 Jan 2008

The mcb is Hager 6A - you can turn the circuit on and off with the mcb but it does not seem to respond to a trip situation.

JohnD · 23 Jan 2008

still time for a new MCB

daytona · 24 Jan 2008

i agree now i know what mcb it is

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Blown bulb tripping circuit but not mcb ???

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