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Instantaneous trip circuit breakers respond to immediate (almost instantaneous) values of current from a short circuit, ground fault, or locked rotor current. |
C This type of circuit breaker will |
never trip from a slow heat buildup due to motor windings overheating. |
• A stuck bearing or a blanket of |
lint covering the inlets and outlets of the motor’s enclosure will cause the motor to overheat and damage the windings. |
• The National Electrical Code |
allows instantaneous trip circuit breakers to be sized to a maximum of 800% of a motors FLA value. |
• They are used where time-delay fuses set at five times their ratings or circuit breakers at |
three times their rating will not hold the starting current of a motor. |
Some instantaneous trip circuit breakers have adjustable trip settings. The instantaneous trip ratings of an instantaneous trip circuit breaker can be adjusted above the locked-rotor current of a motor to allow the motor to start and come up to its running speed. |