220.61 Feeder or Service Neutral Load.
(A) Basic Calculation. The feeder or service neutral load
shall be the maximum unbalance of the load determined by
this article. The maximum unbalanced load shall be the
maximum net calculated load between the neutral conductor
and any one ungrounded conductor.
Exception: For 3-wire, 2-phase or 5-wire, 2-phase systems,
the maximum unbalanced load shall be the maximum
net calculated load between the neutral conductor and any
one ungrounded conductor multiplied by 140 percent.
(B) Permitted Reductions. A service or feeder supplying
the following loads shall be permitted to have an additional
demand factor of 70 percent applied to the amount in
220.61(B)(1) or portion of the amount in 220.61(B)(2) determined
by the basic calculation:
(1) A feeder or service supplying household electric ranges,
wall-mounted ovens, counter-mounted cooking units, and
electric dryers, where the maximum unbalanced load has
been determined in accordance with Table 220.55 for
ranges and Table 220.54 for dryers
(2) That portion of the unbalanced load in excess of 200 amperes
where the feeder or service is supplied from a
3-wire dc or single-phase ac system; or a 4-wire, 3-phase,
3-wire, 2-phase system; or a 5-wire, 2-phase system
(C) Prohibited Reductions. There shall be no reduction of
the neutral or grounded conductor capacity applied to the
amount in 220.61(C)(1), or portion of the amount in (C)(2),
from that determined by the basic calculation:
(1) Any portion of a 3-wire circuit consisting of 2 ungrounded
conductors and the neutral conductor of a
4-wire, 3-phase, wye-connected system
(2) That portion consisting of nonlinear loads supplied
from a 4-wire, wye-connected, 3-phase system
