Motor contactors are relays with large current capacity for connecting and disconnecting motors from power supplies. Most motor contactors are multi-pole devices in order to control all of the current-carrying conductors. Typically, motor contactors are set to a predetermined load value. When the maximum load value is crossed, the overload protection device opens the motor starter control circuit and turns off the motor. For best results, motor contactors should be durable, high-quality, long-lasting devices.

Specifications

Motor contactors work as a protection device for the motor. Two-pole, three-pole, and four-pole devices are commonly available. A three-pole motor contactor consists of a 120 V or 240 V coil. International Engineering Commission (IEC) sizes are lettered and range from B to G. A 4-pole motor contactor has a 40 amp, 240 V coil with a wider current selection range. Specifications include 50-60 Hz dual frequency, AC: 8-1.1 of nominal voltage, and DC: 7-1.25 of nominal voltage in standard and low consumption versions. AC motor starters consist of an overload protection circuit and a motor contactor to ensure that during motor startup, extra current is not drawn. C motor starters are used to turn on/off both motor-controlled equipment and electric motors. AC motor starters also provide protection against low-voltage and power interruption in wires. DC motor starters of 70 W enable fast and simple connection to 24 VDC motors and their sensors.

Types

Motor contactors have DC motor sensors that are one of three types:

• direct starter
• twin direct starter
• reversing starter

Applications

Motor contactors are used in motor control, mercury switch replacement, ramp timing control, and various industrial applications to provide overload protection.

Standards

Guidelines for motor contactors are maintained by National Electric Manufacturers Association (NEMA) and the International Engineering Consortium (IEC). The NEMA rating indicates the horsepower and continuous current rating at the rated voltages. The IEC rating indicates thermal current ratings.

Related Information

Electronics360—Sealed Modules Save Space in Vehicles

Engineering360—Bypass Contactors Put Motor Soft Starters on Cruise Control