I’m confused about what might be causing the 32amp MCB that protects our ring final circuit to trip. Until last week we used rewireable fuses on all the circuits, but then replaced them with MCBs for safety and convenience (there is no RCD in the system). The fuse had previously blown twice in 6 months (I had assumed that this was due to the motor on an old fridge causing an overload when it started up - we only moved in 6 months ago). But the new MCB trips each time it is reset even with no appliances connected to the ring (I swapped around the 32amp MCBs to confirm that it was not an MCB fault – they all tripped).
The MCB trips in anything from 1 second to a couple of hours, and that is what confuses me – I’ve checked and rewired all the sockets, which leaves the cables. The whole flat had a periodic inspection (but no visual inspection of cables) last year and the electrical inspector noticed no problem on this circuit (loads of other problems, but not this one!).
What do you think is happening?
I presume that I am witnessing the operational differences between fuses and MCBs –ie there always was a problem, but the fuse didn’t have the same sensitivity at this level of overcurrent?
If this were a leak from phase to the c.p.c/neutral wouldn’t it happen immediately they touched or touched a common conductive part and not after a variable time – especially as there is no physical movement within the circuit to cause an intermittent fault?
Can I do any useful test with a multimeter or do I need something else (or just an electrician), and what might be the best way to locate the fault without pulling up all the floorboards to do a purely visual inspection of the whole circuit? As they say, “a little knowledge is a dangerous thing”.
Thanks for any suggestions or advice...
The MCB trips in anything from 1 second to a couple of hours, and that is what confuses me – I’ve checked and rewired all the sockets, which leaves the cables. The whole flat had a periodic inspection (but no visual inspection of cables) last year and the electrical inspector noticed no problem on this circuit (loads of other problems, but not this one!).
What do you think is happening?
I presume that I am witnessing the operational differences between fuses and MCBs –ie there always was a problem, but the fuse didn’t have the same sensitivity at this level of overcurrent?
If this were a leak from phase to the c.p.c/neutral wouldn’t it happen immediately they touched or touched a common conductive part and not after a variable time – especially as there is no physical movement within the circuit to cause an intermittent fault?
Can I do any useful test with a multimeter or do I need something else (or just an electrician), and what might be the best way to locate the fault without pulling up all the floorboards to do a purely visual inspection of the whole circuit? As they say, “a little knowledge is a dangerous thing”.
Thanks for any suggestions or advice...
