Contactors

A contactor is a special type of relay designed to handle heavy power loads that are beyond the capability of control relays. Figure 6-5 shows a three-pole magnetic contactor.Unlike relays, contactors are designed to make and break higher powered circuits without being damaged.Such loads include lights, heaters, transformers, capacitors, and electric motors for which overload protection is provided separately or not required. Programmable controllers normally have an output capacity capable of operating a contactor coil, but not that needed to operate heavy power loads directly. Figure 6-6 illustrates the application of a PLC used in conjunction with a contactor to switch power on and off to a pump. The output module is connected in series with the coil to form a low-current switching circuit. The contacts of the contactor are connected in series with the pump motor to form a high-current switching circuit.