II. MOTOR CIRCUIT PROTECTORS
Let’s start with a key problem statement with motor circuits; they have a very dynamic load profile that creates a fine line between acceptable in-rush currents and damaging short circuit events. The initial motor start-up can draw currents more than 15 times greater than what is required to run the motor continuously. A primary function of the circuit breaker is to monitor these currents and open the circuit when harmful current levels are exceeded. These events are often erroneously called nuisance tripping. In-rush characteristics also vary dramatically between standard electrical motor designs and the many new energy efficient motors entering the marketplace. Energy efficient motors have in-rush currents that can be much higher than a standard motor, which has an impact on selecting the correct circuit breaker for the motor. If the type of motor is not known when the equipment is specified or ordered, those issues often pass down to the contractor or maintenance staff installing the equipment.