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Changing Lights to Downlights in Summerhouse and now Tripping Electric

Postby mackroyd » Thu Mar 10, 2016 11:24 am

So, I'm doing a significant garden redesign project and trying to do as much of the work as possible. Part of the project is a summerhouse/shed combo building at the bottom of the garden. I've had an armoured cable run from the house consumer unit to the shed area of the building, into a small consumer unit. From the 6amp MCB in the consumer unit I've run cable to four, four terminal connector boxes. One for a shed bulb, one for some outside under soffit leds, and two for lights in the summerhouse. The outside leds and two summerhouse light switches are all into one four light switch unit. Initially I just wired the two summerhouse lights up to single lamps, but the intention was always to replace these with 7 downlights on each. So up until installing the downlights all worked fine, light switches in the shed, summerhouse and those for the soffit lights functioning perfectly. So I come to install the downlights just replacing the normal (previously working light) with a downlight then linking an additional 6 (typical 50w GU10 halogen bulbs). Did this to both lights, so now two light switches each controlling 7 downlights.
Power back on tried one switch and only the first two downlights lit up. Tried the other switch and it would switch like something might have got inside it and be blocking it from switching. Then the 6 amp MCB tripped? I took apart the light switch just to see if it was debris in it preventing it from switching, I didn't notice any but when I put it back together it was switching fine. So flicked the MCB back, tried out the shed light (fine), outside soffit switch (fine) but any of the two summerhouse downlights just tripped the electric again. I've popped all the downlights out and checked all the connections and all seem sound.
My next idea is to drop down the ceiling plasterboard over the two four terminal connector boxes to check I haven't disturbed anything here (the two for the summerhouse downlights causing the problem are the last two in the chain) when I was putting in the ceiling insulation and fitting the ceiling plasterboard. Before I do however I'd really welcome any advice on whether there should be something else I should be checking. Thanks in advance...
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Simply Build It

Postby ericmark » Sun Mar 13, 2016 12:09 pm

7 x 50W = 350W = approx 1.5A however on switch on there will be far more than that because the tungsten filament takes more current when cold than when hot I don’t know exact figures, but I know when using a lot of lights far better to split them into a number of switches to reduce that switch on surge. As although the max is 1380W the max for a single switch is around 230W or 1A after that you can get problems. To test wiring with GU10’s easy only fit one bulb at a time as does it work OK in every lamp. If it does then it is the switch on load causing the problem. There are two way around the problem, use a C6 MCB instead of a B6 or swap to LED lights. Personally I would use LED lights.
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