Cable/MCB Query
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Cable/MCB Query

Post by chrisrr » Fri Feb 13, 2009 8:44 am

I'm putting a remote CU in the (integral) garage which will be connected from the main cu in the house. The remote cu will supply a small radial circuit (3-4 sockets) AND a lighting circuit. What is the optimum setup for this? ie mcb at main cu, mcb at remote cu, cable size (I was going to use 4mm from main cu to garage cu but nowhere seems to sell it!) Main cu will be rcd protected.

Lighting circuit would be two*outside lamps with pir, and a fluorescent strip 63W.
Many thanks for any help!

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Post by kbrownie » Fri Feb 13, 2009 7:47 pm

Go to electrical wholesaler for 4mm cable, should be plenty about. Garage should have RCD Protection.
Two types of circuit allowed, the number of socket-outlets is not an issue.
20A or 32A mcb with 2.5 t&e or 1.5 micc suppling area of no more than 50sq meters.
32A mcb for 4mmsq t&e or 2.5 micc if floor area no more than 75sq meters.
I use 1.5 t&e on lights with 6A mcb but 1.0 will be ok providing no derating of cable due to ambient temps, thermal insulation, grouping. If a rewirable fuse is being used then correction factor of 0.725 should beapplied. Remember that all circuits should be offered discrimination down the load and where cable sizes change.
cable calc for flo lights are times 1.8 and each luminaire should be assumed to be 100watts.
Oh yes, new circuits are notifiable work and should also have inspect and test certs.

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