MCB triops every 20, 30 mins.

[grandfortune]

HI all,

Got a problem here

about 12 lights on a circuit, IR tests out ok, but the MCB trips about every 15 or 30 mins.

cant for the life of me find the bloody fault, taken everything apart but nothing,, i switch on all lights nothing for 15 mins then trips, i turn off all light nothing, then suddenly trips, how the hell can i test something that's not there, its really doing my head in, Board changed, down stairs neutral borrowed on the landing light so them two circuits on the same trip, no shaver, no fans

one thing i haven't try'd is Changing the LE lamps, but it still trips when all lights are off,, OMG its doing my head in

any ideas going forward

thanks
Grandf

 

[Octopus]

Faulty MCB?

 

[grandfortune]

no its an extension and i was temporarily putting ends in the old board when it started, so ive changed the board now, and changed the MCB for a 10 amp from 6, there has been a chippy working alot there, but cant see where he could have nailed a cable, thats what im thinking of now, but its just that it happens every 30 mins or so, not every 5 mins, or every 2 mins. so bloody strange.

 

[Octopus]

Water getting into a fitting?

 

[ruston]

Or a plate screw just pinching the common in the switch enough to drive you mad.

 

[AP Electrical]

Can you take some of the circuit off and see if that helps locate ie remove leg which feeds6 of the lamps

 

[Octopus]

what type of lights are they?

 

[grandfortune]

pendants and chrome bathroom lights, had all the switches off, most of the switches is where the feeds are, i assume its a dead short and not an earth fault as it doesnt trip the RCD, whats bugging me most is the time on it, the 30mins+, i could live with something getting HOT then tripping but then it wouldnt take that long to trip again if i turned it back on has its hot already if you know what i mean,

i have about 8 new lights in the extension and about 7 old light from the old part of the house. going back on thursday as they are away. so on one will be in the house.

one thing that has happened is a loft extension, so joists have been layed on top of the loft rafters so thats my next cosentration point, but still the timing of the bloody think bugs me, the bloody fault is either there or not.

thanks for the reply' s guys

Grand

 

[Octopus]

Can you disconnect the "new" from the "old" to try and narrow down where the issue may be?

 

[grandfortune]

one thing guys, this circuit has been live for weeks with no problems

 

[Octopus]

one thing guys, this circuit has been live for weeks with no problems

In which case where have other trades been doing work, not looking to point fingers but there could be a correlation between the work and your "fault".

Have fun and do let us know what you find. Faults like this are a pain to locate!

 

[telectrix]

bet you find one of these nasties.

 

[oldtimer]

Have you put all the lights on then clip an amp probe at the CB ? also if stuck swap the supplies over with another circuit and see what happens

ie check what load the circuit is drawing plus if ok and you swap it with another CB then see if that trips as well.

If you dont have an amp probe check Screwfluxout as they have a budget one for about £10 bucks

 

[tony mc]

What were your IR results between Line & Neutral.

And if clear have you tried keeping the test on for a least 1 minute to see if it drops?

 

[ruston]

http://www.electriciansforums.net/asset.php?fid=12261&uid=24526&d=1346064786


This was giving a similar fault to the one you described only it was holding longer at times.


Just dragged that in from attachments. Obviously not the way to do it. How do I get it in as a pic?

To big , but give you the gist!