Multiple lights trip MCB

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Have looked in the FAQ but no answer to this there...
My electrical consumer unit has MCBs. In the house, each light switch controls just one light EXCEPT in the lounge where the light switch controls 10 lights all at once (two pendants each containing 5 bulbs). Whenever one of the lounge lights blows, the MCB trips, but this never happens when any of the other lights blow.
Unfortunately the consumer unit is in the garage, only accessible from outdoors, so when this happens in the middle of the night it's inconvenient to say the least. Is there any particular reason why the lights in the pendants cause the MCB to trip when other lights don't? Is there anything I can do about it?
(The lounge light switch is a dimmer, with press-on-off action.)
Robert
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They might be nearest the CU, and so have the highest fault current.
Your living room lights will blow 10 times more often than the filament lamps in any of your other rooms, simply because you have 10 times more of them. Therefore, whatever the chance of the trip going when a light blows, it's going to happen 10 times more often for a living room light than for any other light.

What is the rating of the MCB (not just the current rating, but the associated type (B, C, or D, or 1, 2, 3, 4 if old)? If it's a type B, 1, or 2, you could probably change it to a type C which might help a bit (but certainly isn't a cure-all). You could change it to a 5A BS1361 cartridge fuse carrier, which will fix the problem. However, a lamp blowing might then kill the dimmer instead -- the MCB tripping may be saving the dimmer from being fried instead.

Use a dimmer which can only be switched on by dimming up from nothing. IME, lights which blow whilst on seem much less likely to arc over than those which do so at switchon, although this is conjecture not backed up by any measurable facts ...
--
Andrew Gabriel

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snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

Or (slightly more expensive) one of those push-on-off dimmers which ramps up over a second or so. Again, no facts but I suspect that these increase the life of filament bulbs.
Hwyl!
M.
--
Martin Angove: http://www.tridwr.demon.co.uk /
Don't fight technology, live with it: http://www.livtech.co.uk /
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These will have no effect on the life of the bulbs, except maybe because they never reach full brightness, so run cooler.
The life of a bulb is actually remarkably stable and related to the evaporation of the filament. Eventually the filament wears down to a point where it breaks. When you turn a light on, it shocks the filament and is more likely to break at this point. However, by the time it gets to this point, it would have broken anyway within about 10 hours if you left it on. We just normally turn the lights on and off enough that it fails during the shock stage.
A big study was done on traffic light bulbs that proved that the flashing amber lights blow after the same period of on time as the red and the green lights. The flashing had no effect on bulb life at all.
Christian.
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Christian McArdle wrote:

That why we all use traffic light bulbs in our houses right?

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green
The failure modes are similar. In other countries, they use long life GLS bulbs anyway.
Christian.
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The research was done in the US, where standard mains lamps have been used in traffic signals, and where long term flashing red and amber signals are used much more than they are here. Lamp life turns out to depend only on the total 'on' time, and not the frequency of switching. This is counter-intuitive because lamps often blow at switchon, but the last switchon only hastened its death by an hour or so which is completely insignificant, and the switchons prior to that had no effect at all on lamp life.
In the UK, we have never used standard mains lamps in traffic signals. Even when they were mains voltage (which they haven't been for years), the lamps were special.
--
Andrew Gabriel

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That is a fact of life with MCBs and filament light bulbs. I'm surprised that other rooms don't trip the MCB, though. When a filament bulb goes, it draws thousands of amps because the shock of the filament blowing ionises the gases into a dead short. Fuses are too cr*p to notice, whilst MCBs actually work, so cut the power.
The solution that works for me is to only use energy saving bulbs. These do not have this problem. Having ten filament bulbs in one room is excessive anyway. Have you heard of global warming?
Christian.
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what is the wattage of each single filament bulb in the pendant ?
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My guess was 10x40W = 400W total. This would go a substantial way to actually heating the room if the insulation is up to scratch. 5W candle bulbs are available on screwfix for 28 for 10, whilst 7W candle bulbs are 43.60 for 10.
Over the lifetime of the 10 bulbs, which is 5000 hours, you will have paid for 350kWh of electricity. The standard candle bulbs will have burned 2000kWh. As they last only 1000 hours, you would need 50 of them, costing 13.77 from the same supplier.
Assuming 6p/kWh.
So we have:
(CFL candle) 43.60 + 21.00 = 64.60 (filament candle) 13.77 + 120.00 = 133.77
The filament candles will have a total cost of ownership more than double the energy saving type. It will also cause almost 6 times as much global warming (except where you use electric heating, where it will be reduced slightly in winter as the heaters won't need to work so hard).
And, don't forget, when they do blow (not so irritatingly frequently) they won't take out your lighting circuit.
Christian.
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That's right.

The pendants came with the house, so I didn't have much choice about the 10 separate bulbs. I'd have preferred fewer bulbs with higher individual wattages. The problem with energy-saving bulbs is that they won't fit neatly into the (decorative) housings... and also that I have a dimmer switch. But the dimmer switch is probably expendable, and the lack of neatness might not be too much of a disaster.
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Not even something like:
http://www.screwfix.com/app/sfd/cat/pro.jsp?tsp078&id 951
Christian.
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Tripe Master wrote:

All MY dimmers are 400W versions.

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wrote:

There are larger ones of course :)
I dealt with a light cluster recently which was on a dimmer switch, and remember the load was about 400w, with the dimmer switch rated somewhat below that, hence why I mentioned it.
PoP
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Outcomes of my investigations:
The dimmer switch was rated for 250W, so it was indeed dangerous. The previous owners were into slight-dodgy DIY so this isn't surprising. Anyway, the dimmer switch has now been replaced with a standard switch (I might consider changing it for a 450W dimmer at a later stage). So many thanks to Tripe Master for pointing this out.
Energy-saving bulbs don't seem to be a possibility: the height available (from the base of the bulb to the top of the acid-glass shade on each housing) is 89mm, and 40W-equivalent energy-saving bulbs are much taller than that. (The housings are designed for 40W golf bulbs.)
My next move is to try a type C MCB instead of a type B.
Thanks to all who replied!
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robert i have fathomed this out very quickly, as your other lights in the house are on a loop in loop out system if one light filament goes then the current (electric) just misses this pendant out and continues to the next tripping the Circuit breaker.With yours no doubt there is a juction box in the ceiling taken from loop in loop out, and it is feeding all the lights in series (ie one to the next and so on in a line). If this is the case then one gone wrong and it all goes. pop into your local b&q warehouse and speak to one of the electricians for some free advice.
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I'm afraid none of this makes sense.
Christian.
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Christian McArdle wrote:

He is thinking of fairy lights on a Christmas tree I think.
Has IMM stated doing elecrical theory from the Bumper Book of How Things Work and changed his alias?

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On Thu, 28 Aug 2003 12:35:29 UTC, "Christian McArdle"

Unless the house is wired with Christmas tree lights!
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Bob Eager
rde at tavi.co.uk
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"alan" wrote | robert i have fathomed this out very quickly, as your other | lights in the house are on a loop in loop out system if one | light filament goes then the current (electric) just misses | this pendant out and continues to the next tripping the | Circuit breaker.
Nonsense.
| With yours no doubt there is a juction box in the ceiling taken | from loop in loop out, and it is feeding all the lights in series | (ie one to the next and so on in a line).
Nonsense.
| If this is the case then one gone wrong and it all goes. pop | into your local b&q warehouse and speak to one of the | electricians for some free advice.
Electricians are not known to frequent B&Q worehouses.
Owain
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