Motor Circuit Breaker Sizing

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

Motor circuit breaker sizing. 1 1 2 3 5 7 10 15 20 25 30 40 50 60 75 100 125 150. Circuit breaker size 2. Locate where your motor falls in table 430 52 based on the full load current and motor size. Unrestrained fault current can cause severe equipment damage product destruction and personnel injury.

High resistance grounding is a means of limiting ground fault current in electrical systems. 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. Table 2 load maximum circuit breaker size of current. The breaker must be sized for 7 6 1 25 10 amps.

22a x 2 5 55a next size up 60a. The table will give you the size of the short circuit protection as a percentage of the full load current. This article will address the history use and recent developments in available high resistance grounding technology used with ungrounded voltage systems. 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.

As circuit breakers cbs and overcurrent protection devices ocpd are designed for 100 rated current i e. Let s try sizing a motor feeder conductor. For an inverse time breaker. Maximum loading of any circuit breaker is 80 of rating for non motor loads with exceptions as noted below.

Therefore it is good practice to size the breaker at 15 amps. This level of protection requires a well designed true dual element fuse. 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. 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. Minimum circuit size is 12 with 20 amp cb. This calculator will also give you motor amps and recommended breaker size starter size heater size and conduit size. Size the branch circuit short circuit and ground fault protection device per 240 6 a and 430 52 c 1 ex.