Old consumer unit, breaker tripping

[Moorea21]

Hi,

I have an old Wickes consumer unit with Get Schupa breakers, the one for the sockets used to trip occasionally, now trips reliably after about 1/2 hour, even with nothing plugges into any socket at all. It's a B32 (32B1M), which is obsolete, I know. It doesn't trip the RCD or anything else.

What are the chances the breaker itself is faulty? Is it worth buying a used one to substitute and test? Chances are I'll end up having the socket ring rewired, and a new consumer unit, but it's maybe worth a try?

 

[ericmark]

It is rare for a MCB to fail, but not unknown, I would test and inspect, and see if I can swap the suspect MCB with another, the MCB's for that consumer unit are expensive, and seems in the main second hand, so I would be considering a consumer unit change.

But much depends on what you can afford, one can test a RCD, but I have never really tested MCB's. Personally I would not want to fit second hand stuff which can't be tested.

 

[Moorea21]

That was what I was thinking. Swapping something that may be dud for something else that may be dud isn't a great bet, although if it stops the tripping, maybe its worth it. As for affording it, I can't afford to burn the house down, so that's always part of the equation.

 

[EFLImpudence]

Put the affected circuit in a different breaker and see if that breaker trips - or vice versa.

 

[Moorea21]

I would do, but unfortunately they're all wildly different current ratings; wouldn't prove anything.

 

[Harry Bloomfield]

I would do, but unfortunately they're all wildly different current ratings; wouldn't prove anything.

Actually it would. If it tripped with no load on it, and you substitute even a 6amp, and that also trips quite quickly, It confirms there is a fault on that circuit.

 

[Taylortwocities]

As it is a ring (it should be), then one way is to estimate the centre of the ring, split it in two and use two 20a MCBs. That would, at least tell you which half of the ring has the fault.

 

[ericmark]

I would do, but unfortunately they're all wildly different current ratings; wouldn't prove anything.

It may well help, this house if I look at the total socket load, in fact total consumption it is not that high.

You can see coffee before going to bed, coffee and a flask 11 am, then another coffee at 1 pm and yet another 3 pm, and a shower at 4 pm, clearly if it trips while making coffee, or having a shower you will have a good idea what has caused it, same goes for washing machines, tumble driers etc. But in the main my socket circuits are not loaded over 4 kW as amps that is 17 amp, so a socket circuit will likely run on a 16 or 20 amp MCB without a problem.

In the main we use 2.5 mm cable, which is rated approx 20 amp, so as a test swapping immersion with sockets assuming the immersion also has a FCU will not be much of a problem, in fact likely you could do without the immersion heater for the time of the test.

To trip a 32 amp type B MCB with a short circuit it needs around 160 amp to flow, the 32 amp is for an extended time, and you can clearly work out if you have over 32 amp load on the circuit by adding the watts, ohms law watts = volt x amps x power factor, you can forget power factor it is nearly 1, so 7.36 kW to over load a 32 amp MCB, also of course a 13A fuse will go before a 32 amp MCB most although not all of the time. To trip a type B 32A MCB before blowing a 13 amp fuse, the current needs to be over 160 amp.

It seems most likely the MCB is faulty, so fitting a 16 or 20 amp is just to confirm what we think is likely cause.

If it were me, as I am not known for throwing money away, I would be looking for another make MCB which will fit. The problem is the buzz bar holes make to make are not standard, so fitting another make could mean the terminal clamp will not clamp well enough with a different make, so change the lot, then all the MCB's do match, clearly no longer a consumer unit as not type tested, now only a distribution unit, but that is one way to get around the problem.

Normally we have a good idea as to the state of the installation, rubber insulated cables point to needing a re-wire, or the plastersizer leaching out green gunge also points to needing a rewire, but wiring from mid 60's is normally still OK. I would use an insulation tester to check for potential faults, one shown cost me £35 new, may be a bit more now.

 

[Moorea21]

Can't seem to get quotes to work, so my reply is all written inline. Sorry about that.

Thanks Harry, yes, that's a good point.

Taylortwocities; that may be an option, but it's something I'd leave to someone who knows what they're doing

ericmark

It seems most likely the MCB is faulty, so fitting a 16 or 20 amp is just to confirm what we think is likely cause.

So, if I understand you right, you're saying swap the 32A breaker for a 16 or 20A one, and see if it trips. Bearing in mind that the circuit trips with the 32A breaker fitted and nothing plugged in, should I also test the 16/20A breaker with nothing plugged in?

a consumer unit as not type tested, now only a distribution unit

Whats the difference? I didn't know they weren't the same.

or the plastersizer leaching out green gunge

is that from the ends of the wires?

I've never taken a breaker out before, so apart from turning the entire house electrics off, whats the procedure? Tools needed? Any potential snags?

 

[EFLImpudence]

Is there not another 32A MCB in the CU? Do you not have a cooker circuit?

If there is then swap the wires into the MCBs.

This assumes that the RCD you mentioned covers both these circuits.

I've never taken a breaker out before, so apart from turning the entire house electrics off, whats the procedure? Tools needed? Any potential snags?

That you have to ask that suggests that you should not attempt it.

 

[Murdochcat]

Could you post a photo of the CU?

MCBs can and do fail ….

Is this the only socket circuit in the property ?

 

[Moorea21]

It is the only socket circuit, yes.
I'm very very cautious with mains electrics; trained service engineer for electronics, domestic wiring's never interested me.

 

[Harry Bloomfield]

So, if I understand you right, you're saying swap the 32A breaker for a 16 or 20A one, and see if it trips. Bearing in mind that the circuit trips with the 32A breaker fitted and nothing plugged in, should I also test the 16/20A breaker with nothing plugged in?

Yes, nothing plugged in, no load at all. If under such circumstances, it would normally trip and doesn't, then it's the original MCB which is faulty. If it also trips, then you have a fault on your wiring somewhere. The latter is the much more likely scenario.

 

[Moorea21]

If it is the wiring, which I kind of expect for some reason, that's going to be difficult to test as it's an old house, and a fair number of the sockets downstairs are on spurs. Not sure if the wiring for the upstairs sockets runs in the loft and down or under the floor and up; either way access isn't great, not to mention that I only just finished plastering and painting downstairs.

 

[Murdochcat]

Just finished plastering and painting. When did the tripping start ?