Motor Circuit Breaker Sizing Chart

Maximum loading of any circuit breaker is 80 of rating for non motor loads with exceptions as noted below.

Motor circuit breaker sizing chart.

Branch circuit conductors that serve a single motor must have an ampacity of not less than 125 of the motor s flc as listed in tables 430 147 through 430 150 430 6 a. Enter the motor horsepower and voltage. As circuit breakers cbs and overcurrent protection devices ocpd are designed for 100 rated current i e. Breaker cannot be larger than ampacity of wire except for motors and a few other loads.

The fuse sizing in column 4 for lps rk sp lpn rk sp frs r and frn r fuses provides a degree of motor and circuit overload protection to back up the normal motor overload protective device. Refer to table 310 16 when selecting the proper size conductor to serve a single motor. 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. Locate where your motor falls in table 430 52 based on the full load current and motor size.

You must select the conductor size from table. Motor wire sizing the nec requires circuits supplying single motors to have an ampacity rating of greater than or equal to 125 of the full load current rating of the motor. The table will give you the size of the short circuit protection as a percentage of the full load current. This level of protection requires a well designed true dual element fuse.

Used when figuring electrical material needs and is already calculated in the chart. The mpcb can interrupt any electrical fault that is. For circuits with multiple motors the ampacity rating of the wire must be at least 125 of the full load current of the largest motor plus the sum of full load currents. Table 2 load maximum circuit breaker size of current resistance loads heat stoves toasters water heater 125.

This table is used to size the short circuit protection check the motor data sheets for the motor s full load current. Protection against electrical faults such as short circuits line to ground faults and line to line faults. 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 fuse sizing in column 4 for lps rk sp lpn rk sp frs r and frn r fuses provides a degree of motor and circuit overload protection to back up the normal motor overload protective device.

This calculator will also give you motor amps and recommended breaker size starter size heater size and conduit size. 1 1 2 3 5 7 10 15 20 25 30 40 50 60 75 100 125 150. Circuit breaker size 2.