Mcb tripping ????

[waitees]

Hi guys

has anyone had this problem before ?

I changed a old board to a 10 way wylex with 2 rcds

the testing was all ok apart from the kitchen, so this was rewired.

Everything is back on all the testing is ok, however as the house
is empty at the moment went back and noticed the downstairs
ring off, thought was odd as I remember turning everything on. Switched it back on and 15 mins later the mcb trips.
Changed the mcb for another, stayed there for a couple of hours all ok switch everything on, all ok, then unplugged everthing again and left.

Went this morning and it had tripped again ! Hardly any load !Took off every socket and checked all ok apart from a fcu had a chunk missing out of the neutral, so fixed that and switched back in all ok at the moment will go back to house tonight to see if has tripped again, not had this problem before if trips again anyone god any ideas what it could.
be ??

[stef]

Hi mate,

Any sockets outside? UT room? It could be a moisture problem. What loads are permanently on?

[GStueyXR]

That's really odd. Have you tried a clamp meter to see if any current is being drawn ?

[waitees]

Hello mate

It only does two rooms and two hall sockets, fcu was for elec rad in toilet, which Is always off, it has also a tv on it a few lamps. Couple of other fcu for wall lights but there all off and got right fuses.

Everything is off and still trips ???? After a while not straight away, as I am not there not sure how long it takes maybe a few hours ?

[stef]

I,d do an insulations test on the rad, maybe the is where the problem lies. If it is not an overload fault (as you said all loads are off) then it is more likely an intermittent earth fault.

[waitees]

But surely if there is a problem with the rad this would not cause a problem when it's off ?

[wirepuller]

I,d do an insulations test on the rad, maybe the is where the problem lies. If it is not an overload fault (as you said all loads are off) then it is more likely an intermittent earth fault.

It wont be an earth fault as the OP states RCD's are installed in the CU and it is the MCB tripping.
Disconnect all loads and do a L-N insulation test, a low reading would indicate a fault or a load somewhere on the circuit you have missed.

[stef]

But surely if there is a problem with the rad this would not cause a problem when it's off ?

Is there a proper isolation switch for the rad or is it just switched off with the thermostat?

That is a strange fault indeed, mate.

[waitees]

Tell me about it ! The mcb I changed was from my stock, so going to buy a brand new one and try that !

The rad is turned off and isolated from the fcu.

I have checked every socket which is only 9 and no probs. Very confusing !

[Guest123]

Going by the descriptions you've given, I'd put my money on the L-N insulation breaking down somewhere in the circuit.

It would be unusual (although not unheard) of to have 2 faulty MCB's like that.

[waitees]

Going by the descriptions you've given, I'd put my money on the L-N insulation breaking down somewhere in the circuit.

It would be unusual (although not unheard) of to have 2 faulty MCB's like that.

Surely the old fuseboard would have detected this L-N fault and kept tripping ??

[Guest123]

Well, what type of old board was it???

[davelerave]

just out of curiosity- what type and size circuit protection before and after

and what type of supply on the installation

[waitees]

It was a old wooden wylex with rewirable fuses, 25mm tails 16mm main earth with tns set up

Was on a old 30amp changed to 32 amp breaker

[davelerave]

tricky one-

assuming replacement mcb is ok and no disturbing loads taking out the 'B' type

and no overload (unlikely)

i'd be inclined to switch on all connected loads- connect L-N together at board and check at 250v to earth as i seen a few odd things happen with L-E short circuits even with rcd protection if memory serves

L-N short circuit seems most likely though

and of course could be totally wrong