Cutler-Hammer Freedom 2100 Series, Руководство по установке и обслуживанию

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12 I.B. 8926-1A
Part 5
INCOMING LINE CONNECTIONS
OVERCURRENT PROTECTION
All ungrounded conductors in a motor control center
(MCC) installation require some form of overcurrent
protection in order to comply with Section 240-20 of
the NEC. Such overcurrent protection for the
incoming lines to the MCC is in the form of fuses or
a circuit breaker located at the transformer
secondary that supplies the MCC. The conductors
from the transformer secondary constitute the feeder
to the MCC, and the “10-foot rule” and the “25-foot
rule” of NEC, 240-21 apply. These latter exceptions
to the general rule allow the disconnect means and
Fig 17 Main Disconnect with Stab Load
Connections
overcurrent protection to be located in the MCC,
provided the feeder taps from the transformer are
sufficiently short and other requirements are met.
MAIN DISCONNECTS
A circuit breaker or a circuit interrupter combined
with fuses controlling the power to the entire MCC
may provide the over-current protection required as
described above or may be a supplementary
disconnect (isolation) means. See Figures 17, 18,
and 19.
Fig. 18 Main Circuit Breaker with Reverse Feed
Fig. 19 Main Circuit Breaker