UK Upstairs light always on

[Macsamillion]

I was asked to help a friend who had an issue with a lighting circuit tripping the main switch. I found a burnt switch and faulty light. Circuit back on, all was good. As I always do I went round checking all room lights. Upstairs landing light had no bulb, got a bulb and put it in. It came on. No matter what position either of the upstairs or downstairs switches were in. Getting 190v at the rose. When the 2 way switche was operated it went to full brightness. I was in all the switches testing so I presumed I had maybe got something wrong in the 2 gang switches. Disconnected and belled everything out. Marked up as all wiring is red( circa 1940's) and reconnected. Still the same. I asked if this has always been the case and why bulb was out and they said it never worked properly but they could switch it off. I exchanged the energy saver for a 60w bulb and the light was off and the 2 way circuit works perfect. No issue with any other lights or the other gang downstairs. Tested switch just using resistance multimeter. OK. Could it be leaking or could the insulation be breaking down inside the conduit onto one of the switched lives. Only live and neutral at ceiling rose.

 

[brianmoooore]

Is the wiring the 1940's original? What is it made of?
Is the 'energy saver' lamp a modern LED type?

 

[pc1966]

1940s wire would make me very nervous, often it would be VIR (vulcanised India rubber) which goes hard and brittle after typically 20-30 years. Though you would sometimes see polythene style plastic which lasts (has quite a glossy / slippery feel).

If it is PVC then probably post 1960s.

 

[Macsamillion]

Is the wiring the 1940's original? What is it made of?
Is the 'energy saver' lamp a modern LED type?

Not sure on exact age of wiring. It's rubber insulated and wrapped in cloth. I believe it's an led type candle bulb.

 

[timhoward]

It's rubber insulated and wrapped in cloth

That means it's at least 60 years old, and potentially much older. You really shouldn't disturb it further, it's seriously past it's shelf life and should have been replaced a very long time ago.
It should now only be touched to replace it as disturbing it will invariably make things worse and even more dangerous.
Please tell your friend that a rewire is urgently needed.

 

[Macsamillion]

That means it's at least 60 years old, and potentially much older. You really shouldn't disturb it further, it's seriously past it's shelf life and should have been replaced a very long time ago.
It should now only be touched to replace it as disturbing it will invariably make things worse and even more dangerous.
Please tell your friend that a rewire is urgently needed.

Absolutely agree. I have recommended it's all replaced. Someone has changed the fuse board for a more modern split board at some point. When I opened the consumer unit it's all PVC wiring. Behind it are maintenance free crimp connections on to this wiring. I also had to change the breaker. I found two lighting circuits wired into a 32A MCB. Very worrying. Typical of old installations it has been modified several times. I just wanted some advice on what could be causing this issue. I believe it will disappear when rewired but I wanted to rule out any incorrect wiring.

 

[pc1966]

I found two lighting circuits wired into a 32A MCB. Very worrying. Typical of old installations it has been modified several times.

That is much worse that an old installation that has been modified!

Originally all lights would be on 5A rewireable fuses, nobody in their right mind would change those for much more than a 6A breaker!

 

[SJD]

Coupling between a permanent L and a switched L, enough to tickle an LED lamp into a reasonable glow when the light is supposedly switched off. Put in an incandescent lamp and you won't have enough coupling to see any visible light.

 

[Macsamillion]

That is much worse that an old installation that has been modified!

Originally all lights would be on 5A rewireable fuses, nobody in their right mind would change those for much more than a 6A breaker!

Yes, kitchen and bathrooms have been renovated and new circuits created so I don't understand why they didn't use 6A MCB.

 

[timhoward]

Behind it are maintenance free crimp connections on to this wiring.

If changing a consumer unit in an emergency situation that is what I do and in my view it's the best way to interface with very old cable. Screw terminals just destroy it. Of course it still needs replacing as soon as possible, but sometimes changing the CU is even more urgent, e.g. if there's no front cover or live parts are exposed.

I just wanted some advice on what could be causing this issue.

LED bulbs can present challenges; induced voltage from other cables can cause interesting things to happen to LED bulbs, especially cheaper ones, including staying on, flashing, or remaining dim.
Normally I'd suggest swapping the two strapper wires over, but on this one I really wouldn't touch it again, it's not worth it!

 

[Macsamillion]

Coupling between a permanent L and a switched L, enough to tickle an LED lamp into a reasonable glow when the light is supposedly switched off. Put in an incandescent lamp and you won't have enough coupling to see any visible light.

Think this is what I done and proved what you are saying. I suppose my question is around the safety. If the light is always sitting at with voltage on it whether it's lit or not

 

[SJD]

The light won't be sitting at 190V or whatever, it will be pulled down to more or less 0V by the load of the lamp.

 

[Macsamillion]

If changing a consumer unit in an emergency situation that is what I do and in my view it's the best way to interface with very old cable. Screw terminals just destroy it. Of course it still needs replacing as soon as possible, but sometimes changing the CU is even more urgent, e.g. if there's no front cover or live parts are exposed.

LED bulbs can present challenges; induced voltage from other cables can cause interesting things to happen to LED bulbs, especially cheaper ones, including staying on, flashing, or remaining dim.
Normally I'd suggest swapping the two strapper wires over, but on this one I really wouldn't touch it again, it's not worth it!

OK thanks. Seems like good advice. Do you think there is still a chance switches are still wired wrongly that I should switch the strapper. I belled them out, marked and grouped the wires with circuit 1 and 2.

 

[timhoward]

OK thanks. Seems like good advice. Do you think there is still a chance switches are still wired wrongly that I should switch the strapper. I belled them out, marked and grouped the wires with circuit 1 and 2.

I actually wasn't suggesting they were wired wrongly, and from what you've posted I don't think it's likely you got it wrong, especially if the light behaves correctly with a normal bulb.
Swapping them over would just be a throw of the dice to change the induced voltage some of the time. But I wouldn't go back inside unless a very fat cheque was being waved in my face!

 

[brianmoooore]

with a LED lamp, it's not unusual for it to glow dimly when off, as a result of capacitive coupling between the live and switched live. With 2 way switching, there's likely to more chance for capacitive coupling, because there's likely to be more switched live and permanent live running alongside each other.
In your case, the problem is likely to be good old fashioned leakage, because the insulation of the wires is breaking down.
A 500V IR test between the wires would confirm, but as said above, there really shouldn't be VIR cable still in use.

 

[Macsamillion]

with a LED lamp, it's not unusual for it to glow dimly when off, as a result of capacitive coupling between the live and switched live. With 2 way switching, there's likely to more chance for capacitive coupling, because there's likely to be more switched live and permanent live running alongside each other.
In your case, the problem is likely to be good old fashioned leakage, because the insulation of the wires is breaking down.
A 500V IR test between the wires would confirm, but as said above, there really shouldn't be VIR cable still in use.

Thanks. It's scary to think that the voltage is induced, but this is what I have come to believe through checks. I did try to check IR between conduit wires but my tester let me down before I got going.

 

[telectrix]

but my tester let me down before I got going.

sack him. plenty mores parks out there need work.

 

[ipf]

Yes, kitchen and bathrooms have been renovated and new circuits created so I don't understand why they didn't use 6A MCB.

Seems like our old friends the 'kitchen and bathroom fitters' have been up to their usual tricks.......... ideal for adding to an ageing VIR system and making things even worse.
After multiple modifications it sounds like a total rip out, to me.
A full EICR at least.