Random Blowing of Lights Circuit (MCB)

Hi,

I am having a problem with the downstairs lighting circuit which I hope someone will be able to help me with.

For the past few weeks, the light circuit is blowing ramdomly, but can be about 10 minutes or so. What is strange, is that this can happen even with all the lights switched off.

I am finding it hard to understand the cause, as logically, a faulty wire should exhibit predicatable results. I would appreciate any advice or tips which i could try in order to reduce the area of investigations. ONe room has a dimmer switch and the kitchen has a halagon light, but the problem remains even with all the lights off.

Your help is warmly appreciated.

Regards Mark

Reply to
Mark Smith
Loading thread data ...

Rats or squrills? Use a megger to find the problem.

Reply to
James Salisbury

I had a similar problem recently - eventually I found a pinched live wire in one ceiling fitting - my guess is that it occassionaly shorted to earth when the fitting was hot. I suggest using a meggar but not everyone has one :)

Reply to
Peter Andrews

A normal DVM should help show this sort of fault too.

Reply to
Dave Plowman (News)

As a first stab, you could disconnect the cable at the CU and measure the resistance between L & N, and L & E using a multimeter. If you get anything other than open circuit with the lights turned off then you have found your problem - now it is a case of following it from rose to rose to work out which cable it is.

If you do get open circuit, then that is where a test with a megger (i.e. high voltage resistance tester) would help next.

Reply to
John Rumm

As nobody has suggested faults between neutral and earth, check this out as this will trip a RCD if neutral to earth volts is significant, like a few volts. I think its about 1v-3v here. If the neutral voltage is drifting about at your location that might explain why it trips at random.

j
Reply to
John

I thought I would leave that possibility out since it sounded like the MCB/Fuse for the circuit was opening rather than a RCD (which if present may not even be protecting the lighting circuit). Perhaps the OP could give us some more details of his setup?

Reply to
John Rumm

Chaps, many many thanks for your expert advice. I havent got a clue what a megger is :-), but I hope my electician knows...

Hopefully a process of elimination will find the bugger...

Cheers Mark

Reply to
Mark Smith

Its like an ohm (i.e. resistance) meter, only instead of using test voltage of a few volts like a multimeter, it uses 500V or more.

The purpose is to find those trickey faults which when measured at DC low voltage do not show up. However at mains voltage the insulation starts to break down (electrically) and conduct making the fault appear. So the megger test does a resistance test at higher than mains voltage to cause the same breakdown to occur, so which you can then detect and measure the problem.

Yup - a binary chop may be the quickest. If you can see a fault with a multimeter then you can disconnect say half the circuit (at a ceiling rose). Keep halving the remainder until you isolate the cable run that has the problem.

(you may find that the cable is fine, but you have a poor connection in a rose - the taking appart and reassembly procedure will probably fix that).

Reply to
John Rumm

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.