Ring circuit failure

[Timothy Murphy]

All the lights (5 in number) in one small circuit in my house have failed - I mean they fail to come on. What is the most likely fault? The circuit-breaker is not affected.

[Roger Mills]

A discontinuity in either the live or neutral. You'll need a voltmeter with a 250v AC scale to find which.

If it's a lighting circuit, it's unlikely to be a ring - just a daisy-chained radial - so a discontinuity in either conductor between the circuit breaker and the first light will kill the whole thing.

I suppose that all the bulbs *could* have failed simultaneously - but that's less likely.

[TMC]

Do they share the same switch ?

Are they low voltage with a shared transformer?

Are they wired from the lighting circuit breaker or from a fused unit on the ring main?

Does the circuit breaker only feed these 5 lights or are there others which still work?

Is the house wired on a loop in system and a feed or neutral has become detached in one of the ceiling roses?

Has a rodent chewed through a cable?

Have you checked for power at a light fitting or light switch?

Regards

[Newshound]

A volt stick is the first thing I'd use when trying to diagnose faults like this in a lighting circuit (or an appliance). And for a ring main, one of those test plugs with three lights is the easy way to spot live or neutral faults.

[John Rumm]

The circuit breaker is knackered...

I bet it is ;-)

However to be sure:

First check that there is not also an RCD protecting the circuit that has tripped. Assuming that is not the case, then the circuit must have failed either at the origin (i.e. the MCB or wiring where it connects to the CU), or the wiring has been interrupted between the CU and the first light on the circuit.

What preceded this failure? Did a bulb blow, did the circuit trip etc?

[Timothy Murphy]

Thanks for your response. I assumed each circuit breaker controlled a ring-circuit; I understand now that that is not so.

OK, I'll bear that in mind as a possible fault. (All I really meant was that the circuit-breaker was not off.)

I wasn't in the house when it happened, but I think it was a spontaneous event.

[Timothy Murphy]

Thanks for your response. No, there are 4 lights (not 5, as I thought) with 4 independent switches. One is in the bathroom, with a ceiling switch (with hanging cord). I think that is the most likely source of the problem.

No

I think they just come from the circuit breaker.

I'm not sure about that. Now I think about it, it seems likely that there are more lights on the circuit-breaker.

I think that is very likely.

Unlikely as this is on the second floor.

No, I'll do that tomorrow in the light.

Thanks again.

[Timothy Murphy]

Thanks for your response. I've got an ancient multimeter, and will test with that tomorrow.

I'll test the bulbs first, but it seems unlikely, as you say.

[Timothy Murphy]

Thanks, I think I've one of those somewhere; but I guess it is not a ring circuit, as I thought.

[The Natural Philosopher]

According to classical physics, there aint no such animal. Everything has a Cause.

[Gazz]

You've gone blind? did you not notice the hairs on your palms as the first sign :)

[John Rumm]

Typical wiring is as in this diagram:

individual lighting points wired like this:

Its not unknown for circuit breakers to appear to be switched on physically, but not actually be on electrically. Been caught out like that myself!

Chances are something triggered it - incandescent bulb failures for example can draw very high currents for short periods. This is often enough to trip a MCB.

What sort of lights are they? Mains halogens for example are very likely to cause MCB trips on failure. Low voltage ones however are not (although could suffer transformer failure)

[ARWadsworth]

Beat me to it.

Or maybe at the first light fitting.

[Dave Liquorice]

Don't believe that, rats and mice are *very* good climbers. The surface of vertical bricks is not a particular obstical to them. Mice can get through a tiny hole as well, 3/8" dia is no problem, 1/2" is a motorway. B-)

[ARWadsworth]

But do they actually chew through the copper?

[Jethro]

But it is possible one bulb blowing can cause a spike which blows another bulb ?

I'm often amazed at how often bulbs fitted at the same time in multiple fittings seem to blow within days of each other ... clearly the manufacturing tolerances are *very* good.

[Gazz]

rats are excelent climbers, i keep pet rats, and they are amazing to watch play, if they want to get somewhere, they will work out a way to get there, we had a wild rat in the space between the celing and upstairs floor boards a few years ago, i found out she'd got in through an air brick, then burrowed up the cavity wall insulation to the top, i lifted a board upstairs, set up a camera and got some good video of her coming out and getting the food i put out for her,

i got rid of her by putting some of my own rats droppings along her runs, made her think she was encroaching on another rat families territory, and she left, saw her down the bottom of the garden in the muck heap later, and let her stay there for winter before turfing her out to go back to live by the brook she came from.

anyhoo, rats can deffo chew through copper, they seem to like the taste of it, one of mine was a bugger for eating scart leads, and he'd usually only eat the wires that were copper, the alli wires in there were left alone for some reason, (i think they were alli, the cable had a mix of copper coloured and silver wires, depending on what signal they were carrying in the scart lead,

it's also been said they are attracted to the power field around wires, another of mine chewed through the modem phone cable once, then proceeded to chew inch lengths out of it going up the live end of the cable towards the phone socket, squeaking each time he felt 90 volts through his mouth as he snipped the cable shorter, that same one had nibbled the insulation off live and earth on an extension lead once too, and tripped the rcd, (he lived to 3

1/4 years old, which is very good for a rat, despite his suicidal tendancies)

[ARWadsworth]

Try again on a non RCD T&E.

[Owain]

And in philosophy it depends on the type of cause. Responsible or morally free actions are caused by our own willings, whereas unfree actions are brought about by causes external to the agent.

Owain