Lighting Circiuts


Postby heffs » Thu May 31, 2007 6:09 pm

Hi,

I'm doing a first fix on a new extension, which will be tested and certificated by a qualified electrician (has to be anyway, since Building Control is involved) and have a question regarding the lighting circuit.

I'm using 230v halogen downlighters in kitchen, and have a three gang switch controlling sets of 5,6, and 6 lamps, each 50W. Then there are 11 other light fittings (6 wall, 1 stairs, 1 utility, boiler room, and two cupboards. Total wattage 17*50 = 850, 6 wall @ 60watt = 360, and so on. So a 6amp mcb will be insufficient, even allowing for some diversity.

So, can I uprate the mcb to 10amp or should I use two circuits? (I've used 1,5mm cable throughout)

Many thanks
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Postby Jeffmo » Thu May 31, 2007 9:04 pm

hi heffs , a 6amp mcb can safely handle about 1200 watts, but in practice should not serve more than ten lighting points . The circuit would overload if lights had high wattage bulbs . However 1210 watts equates to about 5.2 amp , assuming you have low wattage bulbs and allowing 66% of total current demand then you should be ok . Not much room for anymore though , I would split circuit , ie : lights 1 , and lights 2 for instance , this would also allow for more fittings on each circuit.Cheers Jeff
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Postby heffs » Fri Jun 01, 2007 10:19 am

Thanks, Jeffmo, but one further question: if I decide not to split circuit so I don't use another way in consumer unit, is it OK to uprate the MCB to 10 amp to cope with the extra light points?
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Postby sparx » Fri Jun 01, 2007 2:41 pm

Hi as jeff said it's ideal to not put too many on a circuit but as you have used 1.5mm not 1.0mm volt drop not a problem and cable is rated for 18.5A using worst possible installation routes then 10A mcb type B shouldn't be any problem at all,
regards SPARX
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Postby heffs » Fri Jun 01, 2007 2:48 pm

Thanks a lot. Very helpful.
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