Can Wylex plug-in MCB be tripped by anything but overcurrent/short circuit?

[andy27]

Hello, I have an old 16A Wylex SK type B plug-in breaker in the fuse box in my garage which keeps tripping, and every time (and only at that time) the 32A one of the same type supplying the whole garage in my home's main box also trips. It isn't happening fast, sometimes it takes days to happen again after resetting. There aren't any RCDs. There are other trips for the lighting and the freezer in the garage's box but they keep going fine.

This circuit only supplies a couple of sockets and there should never be more than about 3 amps of load on it for now, if that. Nothing's changed with the wiring for at least a decade, there no evidence of anything taking such a large current, and everything works happily when it's reset. Nothing's being switched/plugged/unplugged.

Does this sound like it could just be old age causing one of the breaker to trip and maybe causing the other one to go as well? With one breaker I would just suspect itself but with both tripping together it feels a bit worrying...

 

[littlespark]

Probably just old age.

Maybe the circuit breaker itself, or the wiring it supplies.
There may be short somewhere that is just touching.
Either replace the breaker, and see if that holds, or have the installation looked at.

 

[brianmoooore]

Very tempted to add my first 'dissagree' to an experienced sparky's post on here!
Two MCBs in series have tripped at times, and this will not be 'old age', but because of a serious fault where the current flowing intermittently reaches many tens of amps.
Add the total lack of RCD protection into the mix, and the probably conductive floor in a garage, and you have a potentially very dangerous situation.
If this is a cable fault, it's quite common that the earth wire eventually severs from the arcing (smaller CSA than the live), stopping the tripping and at the same time turning an already dangerous situation into a lethal one.
This needs professional attention ASAP

 

[littlespark]

Disagree all you want Brian.... I was following the OP's description.

If it was a "serious" fault, then the breaker would not reset at all... Unless the breaker itself has become damaged.

The cheap, DIY next step is to change the breaker... which can be done easily if its a push in type (isolate the board of course)

If that doesn't solve it, then a more specialised (expensive) professional needs to look at everything.

 

[brianmoooore]

If it was just one MCB that had tripped, then maybe, but two in series?
Note my comment on severed earth in damaged cable. Seen this many times in pre RCD days.

 

[andy27]

Thank you for your advice. Toolstation had what feels like the last replacement breaker of this type being sold new, so I will give it one last try. Nobody ordinarily goes anywhere near it. Obviously if it still happens with the new one then it won't be going on again until it's been looked at.

Yes it does worry me about having no RCD. Might be time to look at upgrading at least the garage especially if work needs to be done to sort this out.