DIY Doctor UK DIY Forums

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

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

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?

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

Thanks a lot. Very helpful.