Motor Circuit Breaker Sizing Calculator

Table 2 load maximum circuit breaker size of current.

Motor circuit breaker sizing calculator.

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. Circuit breaker size 2. For example the full load current of a 5 hp motor at 460v is 7 6 amps. 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.

Enter the motor horsepower and voltage. 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. 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. This table is used to size the short circuit protection check the motor data sheets for the motor s full load current.

The table will give you the size of the short circuit protection as a percentage of the full load current. Electric circuit diagram template use google drive to make online shareable electric circuit diagrams. Electric motor efficiency calculate electric motor efficiency. Refer to table 310 16 when selecting the proper size conductor to serve a single motor.

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. 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. This calculator will also give you motor amps and recommended breaker size starter size heater size and conduit size. This level of protection requires a well designed true dual element fuse.

Therefore it is good practice to size the breaker at 15 amps. As circuit breakers cbs and overcurrent protection devices ocpd are designed for 100 rated current i e. With no enclosure where the ambient temperature is held at 40 degrees c approximately 104 degrees f. Breaker cannot be larger than ampacity of wire except for motors and a few other loads.

Locate where your motor falls in table 430 52 based on the full load current and motor size. Difference between circuit breaker and isolator disconnector circuit breaker size calculation for continuous non contentious load. Minimum circuit size is 12 with 20 amp cb. Electric motor wiring 480 volt electrical motor wiring data nema amps starter size hmcp size for motors ranging 1 2 to 500 hp.

You must select the conductor size from table.