Contactors and Relays are other names for industrial switches. Both contactors and relays rely on coils to cause contacts to close thus changing the switch from a closed to open position or from a open to a closed position. If the contactor or relay is usually open when de-energized, it is called Normally Open, and vice versa, if it is closed in the de-energized state then it is Normally closed. A normally open (NO) contactor or relay is more common than normally closed (NC). The main reason is that the relay or contactor will "fail" in the open position when power is lost to the coil.
Contactors and relays are used to close a circuit to "turn on" and allow electrical flow into a system or a device. A coil is used to open and close the contacts. The coil voltage can be a different voltage than that is switched. The most common coil voltages are 120/60, 24/60 and 24vdc. The most common switched voltages are 120/60, 240/60 and 480/60.
Contactors and relays are sized in amperes or amps. Also, they come in single pole, double pole, three pole and four pole. The most common are single pole and three pole; three pole for three phase power systems. The two common types of loads are resistive and inductive. A resistive load is normally a heating load. A resistive load does not normally have an inrush current. Howeve, some high temperature heating elements for ovens do have high inrush. Inductive loads such as motors and lighting do have inrush currents and these inrush currents need to be addressed when sizing an appropriate contactor. To figure amps please use our OHM's law calculator.
Types of Contactors and relays are:
Mechanical Contactors
Cube relays
SCR controls
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