June 10, 2002
5-220.127.116.11 Refer to NEC Article 408.16 (2002 Edition) for allowed exceptions to the
Ensure that circuit breakers clearly indicate whether they are in the open (off)
or closed (on) position.
Clearly fill out panelboard circuit directories.
Panelboards should have hinged fronts to allow easier maintenance access.
Place panelboards as close as possible to the center of the loads to be
MOTOR CONTROL CENTERS.
An MCC is a dead-front assembly of cubicles, each of which contains branch
circuit overcurrent protection, motor disconnect means, motor controller, and motor
running overcurrent protection. It is a type of switchboard that usually contains all of the
protective and control devices for the supplied motors.
MCCs with copper bus are recommended for motor control applications and
newer style MCCs can include panelboards, energy monitoring equipment, and other
devices. Refer to paragraph 7 -2 for motor control criteria.
Refer to NEMA ICS 2.3, Instructions for the Handling, Installation, Operation,
and Maintenance of Motor Control Centers, for installation guidance. This NEMA
document also provides practical guidance regarding energization of the new
Fusible disconnect switches should be used where special considerations
require their use. Fuses, fusible disconnect switches, or fusible bolted pressure
switches might be used in combination with circuit breakers when circuit breakers alone
cannot provide adequate fault duty and must be coordinated with current-limiting fuses.
For example, low voltage power breakers alone are often available with short circuit
ratings up to 65,000 amperes. Beyond this level, current limiting fuses are often
Circuit breakers are preferred over fusible switches for general-purpose
applications for the following reasons:
Circuit breakers cannot single phase--all phases open in response to a disturbance.
Fuse replacement is not required.