63A MCB tripping in flat

[mark222]

Hi all,

Just wanted to let you know ablout the job I've been to today and see if anyone has any suggestions.

Called out to a flat with a fault of the 63A type C DP MCB in the communal area tripping when the 6kw electric boiler has been running for ten minutes or so. PME,25mm tails into enclosure housing 63A MCB then out in a 16mm armoured to the consumer unit in the flat.

The RCD and 32A MCB for the boiler circuit in the flat don't trip just the one in the communal area.

The elements in the boiler are giving the correct resistance end to end and the insulation resistance from the element to the boiler casing is fine. I ran the boiler while monitioring the current using a clip on ammeter in the communal area, it was 28A for about ten minutes then the 63A MCB tripped, this could be reset straight away. I'm thinking that the 63A MCB may be faulty because if there was a fault within the boiler I'd expect the 32A MCB to trip before the 63A. Any suggestions would be greatly received? Cheers

 

[NozSpark]

Are there other MCBs next to this 63A one?

Thinking it could be the thermal trip going due to external influences?

 

[mark222]

There are about 6 x 63A MCB's in individual enclosures in the communal area supplying each of the flats.

 

[Chr!s]

Hi all, Just wanted to let you know ablout the job I've been to today and see if anyone has any suggestions.

Called out to a flat with a fault of the 63A type C DP MCB in the communal area tripping when the 6kw electric boiler has been running for ten minutes or so. PME,25mm tails into enclosure housing 63A MCB then out in a 16mm armoured to the consumer unit in the flat.

The RCD and 32A MCB for the boiler circuit in the flat don't trip just the one in the communal area.

The elements in the boiler are giving the correct resistance end to end and the insulation resistance from the element to the boiler casing is fine. I ran the boiler while monitioring the current using a clip on ammeter in the communal area, it was 28A for about ten minutes then the 63A MCB tripped, this could be reset straight away. I'm thinking that the 63A MCB may be faulty because if there was a fault within the boiler I'd expect the 32A MCB to trip before the 63A. Any suggestions would be greatly received? Cheers

Have you tested the distribution cable?

 

[mark222]

Insulation resistance tested on cable, it was OK.

 

[Chr!s]

Insulation resistance tested on cable, it was OK.

Ok

Well, certainly on overload you would have discrimination, short circuit on the other hand its not guaranteed the 32 amp will trip first. Whats the PSSC at the various points on the circuit.

 

[mark222]

I didn't find out the PSCC at various points as I wasn't at the job for long. I'll hopefully be back there later in the week to find out.

 

[Phoenix]

While MCBs do suffer from poor discrimination with each other, I can't see a B32 circuit protective device staying in while the C63 submain breaker pops out, don't beleive that could happen... what is lilely to happen though is a fault would probably cause both of them to trip together.

I'd swap the 63A MCB out for a start and go from there

 

[SLIPSHOD & SLAPDASH]

As you have checked the load it does seem to be a faulty breaker. I would never suggest swapping it with one of the neighbours breakers.

 

[Evans Electric]

How about swopping the 63 for the 32 temporarily and switching the boiler on, see if it holds in.

 

[Technician]

I have heard of this before...shower circuit breakers opening

within 15 minutes of switch-on. Power rating and C/B rating

checked out and all OK following measurement with clamp.

How much heat can a C/B emit when on full chat, Noz? I can

quite understand one of these heating up and affecting the

neighbours.

I have also heard of 'B' type C/B's being replaced with 'C' types

when persistent failures take place.

 

[Dave the rave]

I having a quick educated guess that the breaker is faulty , try changing the mcb and go from there, if not you need to spend more time checking the the ins and out of system,