This depends on the specific model of the PLC. PLCs can be categorized into relay output, transistor output, and thyristor output.
Relay-type PLCs can directly control contactors, while transistor and thyristor-type PLCs cannot directly control contactors.
The maximum output current of relay-type PLCs is 2A, which can drive AC and DC loads. The allowable load voltage is 0-220VAC and 0-250VDC.
The maximum output current of transistor-type PLCs is 0.5A, which can only drive DC loads. The allowable load voltage is 5-30VDC.
The maximum output current of thyristor-type PLCs is 0.2A, which can only drive AC loads. The allowable load voltage is 85VAC-220VAC.
The coil power of the contactor is greater than that of the intermediate relay. The output current of transistor and thyristor PLCs is relatively small, and it is not recommended to directly control the contactor coil. Instead, the intermediate relay coil should be controlled first, which in turn controls the contactor, to reduce the output current from the PLC.
Although the maximum output current of relay-type PLCs is 2A, and they can indeed directly control contactors, based on my years of work experience, directly controlling contactors from the PLC output terminals may lead to damage after 1-3 years of use, with a high probability of failure. In routine maintenance, most output contact failures occur when the PLC output directly controls the contactor.
The usual method for handling damage is to change the PLC program to use spare contacts if available. If there are no spare contacts, the internal relay of the PLC must be replaced, or a new PLC must be installed. (If there is no password, it’s manageable; if there is a password, it can be very troublesome.)
If an intermediate relay is added to the PLC output for signal relay to drive the contactor coil, it can greatly reduce the probability of damage to the PLC contacts and extend their lifespan. I personally recommend that relay-type PLCs also use relays for signal relay.
Amplifier Board
If an intermediate relay is not used for signal relay, an amplifier board can also be used for signal relay.
The function of the amplifier board is similar to that of a relay for signal relay, and it can be understood as being composed of multiple relays (solid-state relays), which reduces the output current from the PLC and decreases the number of wiring terminals.