MOTOR STARTERS

As their name implies, motor starters apply electric power to a motor to begin its operation. They also remove power to stop the motor. Beyond merely switching power on and off, starters include overload protection, as required by the National Electrical Code. The code also usually requires a disconnect and short circuit protection on motor branch circuits. Fused disconnects and circuit breakers provide this and are often incorporated into a motor starter enclosure, resulting in a unit referred to as a combination starter.

Full-voltage starters, also called across-the-line starters, apply full line voltage directly to the motor, either through manual or magnetic contacts. Magnetic starters are used on larger horsepower. Reversing starters, which allow the switching of two leads to change motor rotation, are also usually magnetic.

Reduced-voltage starters, also called soft-starts, apply less than full voltage during the starting sequence of a motor. This reduces current and torque surges, easing the strain on power supply systems and driven devices. Resistors, transformers or solid-state devices can achieve this voltage control. In addition, AC drives offer soft-start inherently.

Both the National Electrical Manufacturers Association (NEMA) and the International Electro technical Commission (IEC) rate starters to aid in matching them to the motor and application.