On 2008-12-19, bill allemann wrote:

I could be wrong, but I think you may also need to derate the wire
sizes because of multiple circuits in the cable, i.e. treating the
12 ga cables like 15 amp, regarding loads and the breaker.

It is necessary to derate whenever you have more than 3 current
carrying conductors in a bundle or conduit. However, the ampacity of
small conductors with 90 degree insulation is higher than the
conventional maximum OCPD. For example, for most branch circuits, #14
can not be fused at higher than 15 amps, but for purposes of derating
the ampacity of #14 with 90 degree insulation is 20 amps. So as long
as your derating factor is at least 0.75, you still get an ampacity of
at least 15 amps. The upshot is that for #10 and smaller, with 6
conductors, there is no need to decrease the OCPD from the usual.

Yours, Wayne