Motor Circuit Breaker Selection

For a 800 kva transformer in 1155 a.

Motor circuit breaker selection.

A motor protection circuit breaker or mpcb is a specialized electromechanical device that can be used with motor circuits of both 60 hz and 50 hz it has several functions that allow it to provide a safe electrical supply for motors. Motor calculations part 1. Eventually the maximum permissible length of the connection is to be considered shock hazard due to touch potential in the case of a short circuit. The best method for providing overcurrent protection for most circuits is to use a circuit breaker that combines overcurrent protection with short circuit and ground fault protection.

Use as branch circuit protection device bcpd acc. Difference between circuit breaker and isolator disconnector circuit breaker size calculation for continuous non contentious load. Transformers in sizes s00 and s0 up to 22 a switching capacity 65 ka or 50 ka at 480 y 277 v. Circuit breaker selection for cbm duty.

However this isn t usually the best choice for motors. Breaking capacity icu required for these circuit breakers is given in the figure h46 as 56 ka. The circuit breaker is designed to break the circuit cutting the power to the motor if the circuit starts pulling too much current. Eaton s motor circuit protectors are ul recognized instantaneous only breakers for motor short circuit protection.

Available in current ratings from 3a to 1200a for use with starters up. The mpcb can interrupt any electrical fault that is. Go back to cb selection tips. When used in tested motor starter combinations they provide complete ul listed motor control and protection and short circuit current ratings up to 100 000a.

There are two types of selection of circuit breaker ratings which require the computation of sc current are. Selection of circuit breaker. The circuit breakers for use in ul markets. Motor protection circuit breakers our motor protection circuit breakers provide both short circuit and overload protection for individual motor loads and are available for a wide range of motor sizes and installation types.

Icu minimum 38 ka from figure h46 the cbm indicated in the table is a compact ns1250n icu 50 ka circuit breaker selection for cbp duty. A 30a circuit breaker can safely carry the exact 30a current but nec suggests 80 as a safe current limit as compared to the rated current. The interesting part about motors is that the amount of start up current and the current the motor uses after it is running is not the same. I rated momentary current and ii rated symmetrical interrupting current.

Protection against electrical faults such as short circuits line to ground faults and line to line faults. For fuseless protection of systems motors and non motor loads e g. The cross section of the connecting leads to the motors are to be selected on the basis of the current setting of the thermal overload release of the circuit breaker. They can be combined with our nema and iec contactors or solid state motor controllers.

Motors and branch circuit conductors.