Motor Circuit Breaker Sizing Calculator

Electric motor wiring 480 volt electrical motor wiring data nema amps starter size hmcp size for motors ranging 1 2 to 500 hp.

Motor circuit breaker sizing calculator. Difference between circuit breaker and isolator disconnector circuit breaker size calculation for continuous non contentious load. Breaker cannot be larger than ampacity of wire except for motors and a few other loads. Enter the motor horsepower and voltage. Locate where your motor falls in table 430 52 based on the full load current and motor size.

Breaker size must be rated for a minimum of 125 of the full load current of the motor it is protecting rounded up to the next standard breaker size. Table 2 load maximum circuit breaker size of current. This level of protection requires a well designed true dual element fuse. 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.

For example the full load current of a 5 hp motor at 460v is 7 6 amps. If the motor circuit overcurrent device consists of an instantaneous trip circuit breaker or a motor short circuit protector as allowed in 430 52 the equipment grounding conductor size shall be permitted to be based on the rating of the motor overload protective device using table 250 122. You must select the conductor size from table. Electric motor efficiency calculate electric motor efficiency.

The table will give you the size of the short circuit protection as a percentage of the full load current. Minimum circuit size is 12 with 20 amp cb. Maximum loading of any circuit breaker is 80 of rating for non motor loads with exceptions as noted below. These conditions per ul 489 underwriters laboratories standard for safety for molded case circuit breakers and circuit breaker enclosures include mounting the cb in free air i e.

The breaker must be sized for 7 6 1 25 10 amps. Electric circuit diagram template use google drive to make online shareable electric circuit diagrams. With no enclosure where the ambient temperature is held at 40 degrees c approximately 104 degrees f. 1 1 2 3 5 7 10 15 20 25 30 40 50 60 75 100 125 150.

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. 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. Therefore it is good practice to size the breaker at 15 amps. Refer to table 310 16 when selecting the proper size conductor to serve a single motor.

Circuit breaker size 2.