outside lighting fault tracing

[ifmhome]

HI all
I have 3 separate lights in my drive (all low wattage energy bulbs) controlled via a standalone PIR - installed sometime in last 20 years by previous owner

Recently the 5A mcb at the consumer unit wont stay 'live' - it keeps tripping, breaking the circuit.

Cable is armoured and buried underground and I have :

- checked and replaced all 3 bulbs
- checked for clean connections on the wiring blocks in each light fitting (I actually replaced each block)
- replaced the PIR

After each of the above steps I tried to reset the mcb but only on the last step did I get any success - The mcb did reset for approx 30 secs - then again for a couple of minutes, but now trips immediately, as before

I dont want to dig up the cable (long run, and I dont know how deep it was buried by previous owner) without knowing where the fault is - can anyone suggest other diagnostics or approach to finding out what the problem is and/or where it is ?
Many thanks

Ian

 

[pjcomp]

Disconnect each point and check the continuity on each leg of the circuit - if you find a short on one of the legs that's the one to dig up ...

Alernatively it could be the MCB has gone to its maker - are you able to/capable of changing the circuit to a different MCB to see if the problem stays or comes with you?

PJ

 

[ifmhome]

Hi
Many thanks for your reply

I have already swapped a working mcb in, so can rule that out

How can I test each light point for contiunuity without power (the mcb trips) ? the cable run (under ground is over 100ft)

Thanks

Ian

 

[BigJon]

Disconnect all your lights and put your mains cable in connector, if MCB still trips then the cables damaged.
If the MCB holds, connect your lights up one by one and see if you can narrow it down to one or several fittings, maybe water has got in and corroded the lamp holder.
Ideally an Insulation resistance test would be ideal but I appreciate you won't have a meter to test.

 

[ifmhome]

Hi BigJon
I do have a meter, and a basic understanding of how to use it
What I am unclear on is the first part of your mail
I can only access the cable as it comes into the first (and then subsequent ) lamps - I cant (wont !) open the mcb holder, and from the consumer unit the cables are underground and not accessible ?


BTW - hope its dry up there - we have yet another flood down here )

Thanks again
IAn

 

[RF Lighting]

I think you're probably going to have to get some one in to ake a look at this for you, as ideally the circuit needs breaking down into sections, and then an insulation test carried out on each section.

This will tell you which part of the installation the fault lies on, and also whether the fault is a dead short or just a low resistance fault.

 

[BigJon]

Hi BigJon
I do have a meter, and a basic understanding of how to use it
What I am unclear on is the first part of your mail
I can only access the cable as it comes into the first (and then subsequent ) lamps - I cant (wont !) open the mcb holder, and from the consumer unit the cables are underground and not accessible ?


BTW - hope its dry up there - we have yet another flood down here )

Thanks again
IAn

what you need to do is totally disconnect the cables that go in to the lights and put them in connector/chock bloc ( Reds together,Yellows together & blues together*) effectively taking the lights totally out the circuit so what you really have is 1 long cable run with 3 joins in it.
If the MCB holds your in luck as its only a faulty fitting, you then will connect 1 light at a time to narrow down the faulty fitting
Alternatively disconnect all the cables and bell them out a piece at a time, making sure they are clear - i'e. no continuity between Live, Neutral or Earth.
Also have you been drilling or digging recently, just incase you've hit the cable?

*I'm presuming its 3 core armour cable you have.
Cheers