"430.26 Feeder Demand Factor. Where reduced heating of
the conductors results from motors operating on duty-cycle,
intermittently, or from all motors not operating at one time,
the authority having jurisdiction may grant permission for
feeder conductors to have an ampacity less than specified in
430.24, provided the conductors have sufficient ampacity
for the maximum load determined in accordance with the
sizes and number of motors supplied and the character of
their loads and duties.
FPN: Demand factors determined in the design of new facilities
can often be validated against actual historical experience
from similar installations. Refer to ANSI/IEEE
Std. 141, IEEE Recommended Practice for Electric Power
Distribution for Industrial Plants, and ANSI/IEEE Std.
241, Recommended Practice for Electric Power Systems in
Commercial Buildings, for information on the calculation
of loads and demand factor.