Molded-Case Circuit Breaker
Supplementary Protector
In testing, must be able to interrupt its rated fault current
and remain operational after the fault.		 In testing, only may need to interrupt an overcurrent;
may be nonoperational after a fault current is imposed.
Intended to provide conductor protection in accordance
with the National Electrical Code (NEC).		 Not evaluated to provide conductor protection and
cannot be used in branch circuits.
Not allowed to rely on a series protective device for
conductor protection.		 Allowed to be tested with a branch-circuit device in series with
the supplementary protector.
Required to protect downstream wiring and appliances. Used in an appliance; may provide some wiring and
appliance protection.
Cannot rely on other devices to provide overcurrent
protection as defined in the NEC.

May rely on a separate device to assist with short-circuit
and ground-fault conditions, such as a branch-circuit protective
device or a separate in-line fuse.
Has minimum short-circuit-interrupting ratings of
5000 A at 250 V ac and 10,000 A at above 250 V ac.		 Has a typical maximum short-circuit current rating of 5000 A,
but need not have been evaluated for short-circuit conditions
during the recognition. May be evaluated for greater than 5000 A
and may be evaluated at any value declared by the manufacturer.
Typically mounts in listed circuit-breaker panelboards. Typically mounts (as a component of a listed assembly) in
appliances or on DIN rails and is typically smaller than a
molded-case circuit breaker.
Always listed (but beware of confusion of a listed motor
control with a listed molded-case circuit breaker). 		A recognized component.
Required to close on fault conditions. Typically not required to close on fault conditions.
Has trip-curve characteristics developed for protection of
branch and feeder circuits.		 Has no standard trip curve established by the product safety
standard to ensure protection of conductors in the event of an
overload or short-circuit condition.
Carries no conditions of use (acceptability). Carries specific conditions for use (acceptability) that must be
followed to ensure that the device will meet minimum electrical
fire and shock requirements.

Table I. A point-by-point comparison of the application conditions and requirements of molded-case circuit breakers and supplementary protectors.