NPFC - MIL-PRF-39019
CIRCUIT BREAKERS, MAGNETIC, LOW-POWER SEALED, TRIP-FREE GENERAL SPECIFICATION FOR
|Publication Date:||27 June 2017|
This specification covers the requirements and test procedures for single and multipole, trip-free, sealed, low-power, magnetic circuit breakers with current ratings of 0.050 amperes to 20.0 amperes inclusive, up to and including 240 volts, 60 hertz (Hz) and 400 Hz alternating current (ac), and 50 volts direct current (dc) (see 6.1 and 6.7). These circuit breakers may also include auxiliary contacts (see 6.6.1) and terminals for monitoring circuits. Designers are CAUTIONED that these circuit breakers may contain a pure tin finish on some of the component parts (see 6.5).
General. Circuit breakers covered by this specification are intended primarily for use in the protection of electronic circuits and should be used where starting inrushes of transient... View More
General. Circuit breakers covered by this specification are intended primarily for use in the protection of electronic circuits and should be used where starting inrushes of transient overloads are neither heavy nor prolonged and the equipment must have relatively fast protection. These circuit breakers are military unique in that they must operate satisfactorily under the following demanding conditions: Endurance testing of 10,000 mechanically performed make and break operations while energized to 100% of rated current, and they must be fully sealed when submersed in addition to being panel sealed. These requirements are verified under a qualification system. These circuit breakers should not be used in circuits (e.g., primary power circuits of electric systems) whose short circuit current potential is greater than the interrupting capacity of the breaker unless the circuit is properly protected by other means. These circuit breakers are not switches and should not be used as such (see Engineering Practice Study, "Using Circuit Breakers as Switches" for more information).
Derating. Circuit breakers should continuously carry normal load current; however, the value chosen should be the lowest rating that will not open the circuit breaker inadvertently. The following factors should be considered in selecting the proper current rating and time delay curve of a circuit breaker:
a. The average (steady state) conditions of the load.
b. The initial start-up current and duration of the current of the equipment to be protected.
c. Transient overloads and their duration.
d. Comparison of the time delay characteristics of the circuit breaker with the time current characteristics (including starting or overload surges) of the equipment, component, or wire.View Less