The continuous current ratings of low-voltage power circuit breakers (LVPCB) range from 15 amperes with interrupting ratings of 22,000 amperes symmetrical at 480 Volts up to 4,000 amperes with interrupting ratings of 85,000 amperes symmetrical at 480 Volts, or 130,000 amperes at 240 Volts. Models are available that are rated at 3,000 amperes with 150,000 amperes at 480 Volts and 200,000 amperes at 240 Volts. These maximum interrupting ratings are available only when the LVPCB uses instantaneous trip coils. Breakers that use relays or selective trips have short-time ratings which are lower than these maximum ratings. These delayed or restrained trips are potentially useful when coordinating protective devices to minimize the extent of the circuit affected by a short circuit.
LVPCB are made in either draw-out or stationary models. The draw-out models provide the greatest degree of convenience and safety when the breaker is to be serviced or inspected. They are built with heavy-duty contacts, arc quenchers and appropriate operating mechanisms which are either manual or electrically operated.
Protective Systems
Rating Of Low-Voltage Power Circuit Breakers
