Sometimes when a bulb blows (ceiling light) it causes the ELCB for the circuit to trip. That is, if the bulb is in one of the upstairs rooms, only the upstairs lighting ELCB is tripped. The power points are unaffected, as are the power points and lighting circuits downstairs.
Is this just because modern wiring is so much more "safe" than once was the case? This house was built in 2004.
MM
I suspect you don't mean earth leakage trips..its uncommon to have those on lighting circuits alone..
Yes, its very common for bulbs to trip a standard MCB.. as they arc on failure and draw quite large currents before burning out. Mine do it every time..I s'pose I could replace then with slower acting ones..but I can't be arsed..
RCD's can also trip if they are marginal, and there is a lot ofcapaicatbce between live or neutral and ground..
Out of interest, how do they specify slower acting ones ? I've never seen them, but then for a twice-a-year event (the MCB tripping on bulb blowing) I also fall into the CBA category ...
Are you sure you mean ELCB? It would be an unusual domestic installation which had these on individual lighting circuits. Sure you don't mean MCB?
Standard MCBs trip in a shorter time than a wire fuse takes to blow, and bulbs often draw excessive current at the instant when they blow. Plenty of theories on why - you'd probably find them by Googling.
The message from The Natural Philosopher contains these words:
They also are supposed to have fast-blow fuses inside each bulb these days to stop this happening. Does it? Does it hell!
Type C instead of te more common type B. A bit less prone to nuisance trips.
NT
AIUI though, the reason for the trip is just before the filament blows, an arc is created, which has a very low (almost infintesimal) resistance which leads to the current draw being astronomical (almost infinite) certainly in excess of 200A.
It's the speed that the MCB reacts with that causes the trip. I would have though that even a type C would trip when a bulb blew ?
The message from jethro snipped-for-privacy@hotmail.com contains these words:
Just after, surely? While the filament's still intact there's little localised potential difference from which to strike an arc.
As I understand it, as the break opens a small spark starts - easy enough to do as the gas in the bulb is already hot as is the filament - and the arc being very low impedance and most imporantly /mobile/ is able to run along the filaments towards the leadwires introducing what is damned nearly a dead short.
A better description than mine ! Anyway, the point is that for a split second the current draw is trying to climb to infinity. So irrespective of the *current* tolerance on the MCB, it would still trip.
Really I need to get one which only trips if the current drawn exceeds the limit for (say) more than a millisecond or two.
Not all do. Candle bulbs are the worst offenders..
That's my understanding, more or less.
Like the rest I reckon you've got ELCB's and MCB's muddled. If the ELCB went then the whole house would in all likelihood go down. As you've got a modern house I suspect you will have a split consumer unit in which the lights are NOT off the ELCB so that if an earth leakage occurs in an item on the power circuits and does trip the ELCB, then the lights will remain on.
Having said all, thanks for asking the question as I've recently done a CU replacement and was heading towards asking the same one due to the nuisance trips when a bulb fused. I'm surprised at one contributor who reckoned he only got 1 or 2 a year - he must buy better quality filament bulbs than me as I get one every couple of months.
Rob
I mean the switches in place of the fuses of yore. My consumer unit contains a whole row of them. Mostly black, some red.
MM
Seems like CBA applies to me, too! When the bulb went late last night, I'd already switched on the bedside light, so I thought, stuff it, I'm not going to grope my way down to the kitchen now, find the torch, open the inner garage door, get the stepladder and clamber up to the consumer unit.
I didn't actually get round to flicking the switch back up until about
9 a.m. this morning.MM
In my house the switch doesn't /always/ trip. Just mostly.
MM
Yeah, probably I do! I just mean the switches fitted as standard nowadays where my old 1947 council house had push-in fuse holders.
MM
Well, I only buy the cheapest bulbs, Tesco's or ASDA's Smart Price brand. They seem to last as long as any other and are dirt cheap. I reckon I replace two or three a year, tops. Most bedrooms, however, never have them switched on from one month to the next.
MM
The message from The Natural Philosopher contains these words:
Don't have any handy to peep at.
On 12 Dec 2006 08:17:53 -0800 someone who may be jethro snipped-for-privacy@hotmail.com wrote this:-
Only if the MCB trips instantly. However, no circuit breaker operates instantly, for the rather obvious reason that there are a number of mechanical bits and pieces which need to move before the circuit is opened.
On Tue, 12 Dec 2006 13:25:17 +0000 (GMT) someone who may be "Dave Plowman (News)" wrote this:-
That rather depends on the situation.
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