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Lights going out no bulbs blowing

Postby blackcabmal » Mon Jan 17, 2011 9:43 pm

I have a perplexing problem with my lights.
my consumer unit lighting circuit keeps cutting out without any bulbs blowing,i flick the switch and all is normal again.
This is happening periodically sometimes 2 times an evening sometimes not for 2 weeks.
we had a loft extension a year ago and the lights were put on the same circuit and had thought it was overloading but has happened without any of those lights being on as well,so i am confused,any pointers to the problem would be gratefully received.
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Postby ericmark » Tue Jan 18, 2011 10:21 pm

There are two types of trips.
MCB These limit power.
RCBO These limit power and monitor earth leakage and will have a test button.
Which do you have? If it is a RCBO then there could be an earth fault.

If a MCB these have two trips one magnetic and one thermal. The latter can take some time to warm up. So with a B6 MCB the continuous load needs to be below 1380W to allow for some degrading of the trip we will say 1250W.

With say with my house before energy saving bulbs were fitted 6 x 60 in living room, 3 x 60 in dinning room and 2 x 60 kitchen and a 60W in all bedrooms and bathroom and garage we have a total of 1020W well with in the limit. However start putting halogen spots in the kitchen and just 6 lamps takes us over the limit.

Today with 10 x 8W in living room and 6 x 8W in dinning and still 2 x 60 kitchen but 11W else where the total has dropped to 300W around a 1/3 of what I did use so adding wall lights in bedroom and extra lights in garage I am still well within the supply a 6A MCB can give.

So count the light bulb wattage and aim for no more than 1250W.

Of course MCB's can go faulty so if you are below than may be it is faulty.

However mice and rats have also from time to time caused MCB's to trip so if your bulb count shows it should not trip I would get an electrician to check the circuit although a insulation tester will not always find rodent damage it often does and worth getting it checked not just changing the MCB.
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Postby bobthebodger » Thu Jan 20, 2011 3:22 am

Before going so far as to having all the lighting circuits tested, you could first try testing/replacing all the bulbs in your house. Could be that you have a faulty bulb, that is on the blink bad enough to trip the RCB (very sensitive things) but not enough to actually blow. I've had similar problems in the past.
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