intermittent fault

[GPack]

Hello. I could do with a bit of help with a problem I have at the moment.

I have a customer who has some outdoor lights that just won't stay on. It is a big garden and the route each of the cables take are not completely known, or where some of the terminations are. The consumer unit has also been built around with a kitchen cupboard. This means I couldn't get into it!

From an internal kitchen lighting circuit switch is a switch fused spur for the outdoor lights. When ever the fused spur is turned on the MCB (it is not RCD protected) turns off. After checking the bulbs where ok and trying to piece together how the circuit was run to conduct some tests I left and returned a week later. I tried the outdoor lights and they came on. Couldn't believe it.

Had another call today to say that after the lights had been on for 5 minutes, they tripped the MCB. Once again, all bulbs are ok. The weather has been dry between the lights working and then not.

Any ideas please??

 

[Guest123]

Are you sure the circuit is not overloading???

You say they tapped off the kitchen light switch, how many lights are there in total, both inside and out and what rating of MCB???

Either that or an intermittent short circuit fault perhaps, arcing with sometimes making enough of a connection to operate the MCB.

 

[GPack]

There are about 8 out door lamps and 9 kitchen down lights.
The MCB is a 6A
The fault has appeared when the kitchen lights are off so likely not to be an overload.
I think the arcing over is a real possiblity.

 

[Guest123]

Seems like stripping fittings down, checking connections and joints, and testing of the wiring is the way to go.

 

[Deleted member 9648]

IR test the external lights at the load side of the spur....this will establish whether there is a fault or not.....that is always the first step.
I've known mcb's to stay in for long periods with very low IR readings.

 

[Andyfm]

Sounds like it could be water getting into an outside light or connection somewhere, I would isolate the outside section and try to IR test to find which section of cable or light fitting is at fault.
Often found in the past that water doesn`t always trip an mcb immediately, it can take a while.

 

[eskimo39]

The only problem you may have IR testing is that if the fault is intermittent it may show clear. Obviously the ideal time to test them is when the MCB won't stay in.

An other thing you could try is to split the outside lights into 2 circuits (isolating one half of them) to cut down the amount of points that could be faulty.

 

[GPack]

Sounds like good advice. I'll give it a go and let you know how I get on.

Thanks

 

[eskimo39]

Good Luck

 

[pevvers]

I would consider changing the MCB out as well, as this could be at fault.

I ripped apart a whole external lamp post installation and tested insulation resistance on every leg and found everything clear, only to discover that it was the MCB going faulty when it had load on it. Sometimes it held for hours, sometimes for minutes, sometimes not at all. So it's certainly worth looking at too...