Lighting fault.

[Megaohm7]

I.ve been trying to trace a fault on a lighting circuit where a voltage of 3v is present when the lamps are switched off. I have switched off breakers in turn and discovered that when the ring final circuit is switched off the 3v dissapears from the lighting circuit. I'm thinking along the lines of borrowed neutral somewhere but will need floors to come up to find JB's. The lighting circuit is in need of rewiring as it's old rubber insulation and it is perishing. Just waiting for client to say what they want to do. If it was my house then I would rewire it. ray

 

[batty]

3 volts induced voltage rubber cables are past sell by date though.

 

[Megaohm7]

They sure are I will post some pictures later but I have pointed the dangers to the clients .

 

[SPECIAL LOCATION]

I.ve been trying to trace a fault on a lighting circuit where a voltage of 3v is present when the lamps are switched off. I have switched off breakers in turn and discovered that when the ring final circuit is switched off the 3v dissapears from the lighting circuit. I'm thinking along the lines of borrowed neutral somewhere but will need floors to come up to find JB's. The lighting circuit is in need of rewiring as it's old rubber insulation and it is perishing. Just waiting for client to say what they want to do. If it was my house then I would rewire it. ray

3V on a circuit while lamps are switched off??

This is NOT a fault.. :C

sounds more like normal characteristics of an electrical installation where multiple live cables are in close proximity to each other..

often running for several meters under floors, above ceilings through joists..

and using a cheap electronic multimeter.

The technical reason is to do with electro magnetic effects inducing voltages from one cable to another..

and the fact that the multimeter doesn't put any real load on your cable to consume the induced voltage.

e.g.

I just got an off-cut of 1.5mm T&E rested it by some ring main cables and I got "6v" between the live and a near by water pipe..

and 1.5v if the cable was just lying on the floor!

At all times both ends of the cable are just lying open not connected!!!

similar principle to Radio & TV aerials picking up signals in the air and inducing voltages onto the antenna down lead

3V is not likely to be any fault.

:|

 

[nsbs]

3v at a lighting circuit with rubber cable is common. as previously said its likely to be an induced voltage.

ian

 

[xrford]

Only prob has to be a few meters next to a live cable to induce a small voltage especially if the insulation is breaking down as well. I probably wouldn't worry about that and perhaps start seeing how big of a job it is for re-wire...

 

[jsa986]

If rubber cable is present and indeed perishing then id suggest a periodic report is carried out, then advise accordingly.

 

[Megaohm7]

If rubber cable is present and indeed perishing then id suggest a periodic report is carried out, then advise accordingly.

I have suggested from what I've seen that a rewire would be the best and safe option but a PIR would help to show up any other problems on the other circuits..

 

[Doc Hudson]

If rubber cable is present and indeed perishing then id suggest a periodic report is carried out, then advise accordingly.

If rubber cable is present approved document P recommends it is left undisturbed and replaced at the earliest convenience. PIR testing could cause more faults than it identifies.

Doc H.

 

[Megaohm7]

If rubber cable is present approved document P recommends it is left undisturbed and replaced at the earliest convenience. PIR testing could cause more faults than it identifies.Doc H.

I have had a few experiences with rubber cable now and it is enough to leave well alone as at first I couldn't believe just how brittle the insulation could get. I tend to learn by my mistakes.

 

[Doc Hudson]

I have had a few experiences with rubber cable now and it is enough to leave well alone as at first I couldn't believe just how brittle the insulation could get. I tend to learn by my mistakes.

Especially around light fittings, it almost falls off with your breath. Junction boxes and CU connections can be easier to disturb without all the insulation falling off. But anywhere involving heat, like in the back of light fittings, should be avoided like the plague in my opinion.

Doc H.

 

[batty]

Especially around light fittings, it almost falls off with your breath. Junction boxes and CU connections can be easier to disturb without all the insulation falling off. But anywhere involving heat, like in the back of light fittings, should be avoided like the plague in my opinion.Doc H.

I did a rewire a few years back and this had wooden fuse boxes now when I tried removing some of the circuits which had been rewired the insulation just fell off some of the other circuits when trying to pull the cables out . I ended up having to remove the wooden board and then put a tempboard in to reconnect some of the rubber cables to keep them going until they were rewired. I think if the insulation gets air to it it will perish yet if you strip it back its like the day it was manufactured very strange indeed.