Sparky,
The 5% in the NEC is not a rule, but only a FPN.
Stu,
On large circuits, oversized wire may inpact the available short circuit current requiring breakers with a higher interupting rating.
I can't see any advantage to oversizing the conducotrs too much. However many times the cost of making the conductor one size larger wil be payed back in a year or two in the reduced electrtical usage if the circuit is almost always on.
Don(resqcapt19)
