Currently refurbing a bungalow. One of the lighting circuits has stopped working. None of the lights work, but the RCD doesn't trip. I've checked all the connections in the ceiling roses and light switches. All looks ok. I've also checked all the junction boxes that I know of in the loft and they look ok too. In a moment of frustration yesterday I switched the power off and took all the bulbs out. Then I replaced with spare bulbs and switched power on. Now it appears to be fine. Could a dodgy bulb cause this?
Can a dodgy bulb cause a lighting circuit to fail?
- Thread starter lizzy
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Still sounds like a dodgy connection somewhere, that is if nothing tripped in the consumer unit. A faulty lamp can cause an MCB to trip. Did you really mean RCD??
As it is all the lights, it could be faulty connection in the consumer unit, itself….
When you were checking connections, how did you do that? Just eyesight, or do you have some form of test meter?
Also, what
As it is all the lights, it could be faulty connection in the consumer unit, itself….
When you were checking connections, how did you do that? Just eyesight, or do you have some form of test meter?
Also, what
work have you done on the lighting circuits??
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A single dodgy bulb could not cause all lights to stop working unless it resulted in something tripping.
Did all the lights stop working suddenly and simultaneously and, if so, what work (not necessarily electrical) were you doing at the time this happened?
I agree with TTC that a loose connection (that somehow got disturbed) probably remains the most likely possibility. On the face of it, if replacing all the bulbs causes all to start working, the most obvious explanation is that all were dead! However, that seems pretty unlikely, but there are two other possibilities which come to mind - (a) that removing/replacing the bulbs re-disturbed a loose connection or, (b) that the circuit's MCB had actually tripped (without it being obvious) and that your switching the power off, and then back on again (assuming you did that with the MCB), may have reset the MCB.
Kind Regards, John
A lamp blowing can also cause an RCD trip.
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I suppose nothing's impossible but, with most sort of lamps/bulbs, I would have thought that it would be extremely unlikely.
Kind Regards, John
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I have known that too, but cannot explain why it would do that!
I think Bernard can and has.
I believe he has, but I think he talks about a scenario which, as I've just written, I think would be "extremely unlikley", at the very least!
Kind Regards, John
It's certainly much less frequent an occurence, but it can and does happen on occasion.
As does RCD tripping when something is switched off.
Indeed, and in both cases it is difficult to hypothesise credible mechanisms - and, again in both cases, those hypotheses require circumstances which are probably "very unlikely".
Kind Regards, John
thanks all. it didn't trip anything. The only thing that has been touched on that circuit is we had a sparky put a feed in for an extractor fan, which I have since wired up from the isolation switch. But the fan isn't live and still isolated with the switch. but the lights have worked since then. When I say I 'checked' all the connections I was just looking for the security of the terminals and they all appeared ok. The lights still didn't work after securing all the ceiling roses and switch plates back. It was only after removing the bulbs. I guess I never checked the bulb holders themselves, but then they would just be the same as a dodgy bulb.
Unless it tripped something, a problem (e.g. loose connection) in one bulb holder would not affect all of the lights - only the one concerned.
In your position, I think I would be tempted to replace all of the original bulbs (if I still had them), one at a time - to see what happened!
Kind Regards, John
The reason that an RCD may trip when a lamp blows is most likley to be as follows.
The failing lamp becomes very low impedance (*) and for a few milli-seconds an extremely high current flows. This ( hopefully ) trips the MCB but until it does the high fault current flows along the Live through the RCD sensor. The Neutral current should also all flow through the RCD sensor and cancel the effect of the curent on the Live. There is a sneak circuit which diverts some of the Neutral current to bypas the RCD sensor.
The high fault current flowing through the impedances along the Neutral causes the Neutral in the lighting ciruit to rise to a significant voltage above ground and the CPC. Capacitive coupling between Neutral and the CPC allows for some of the fault current on the Neutral to flow into the CPC. The portion of the fault current that flows along the CPC bypasses the RCD sensor and hence Live current and Neutral current through the RCD sensor are not equal.
(*) A filament lamp can create a plasma like discharge through the metal vapour of the burnt out filament. This can be a dead short with a fault current of over a 100 amps for one or two cycles until the lamp shatters or a safety device ( MCB or RCD ) operates. Electronic modules ( LED drivers, electronic "transformers" etc etc ) are unlikely to create such a high fault current but nothing is impossible. ( especially when considering the poor design and construction of low cost items from dubious sources )
Is it a repo?
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