Trade-Offs in Overload Protection for Low Voltage Motors

Running overcurrent protection for motors rated 600 V or less is available in a variety of devices. Thermal overload relays, thermal protectors, magnetic and solid-state overload relays, multifunction solid-state motor protectors, and even short-circuit protective devices selected according to certain rules of the National Electrical Code (NEC) can provide varying degrees of protection. Selection of the running overcurrent protective device is based upon application requirements, cost, convenience, and performance. The advantages and disadvantages of each method of providing overload protection for three-phase low-voltage motors in a concise manner are outlined, so that an individual selecting overload protection for a motor circuit can be aware of the many considerations and select the overcurrent protective means that optimizes the concerns he feels are most important.