It depends. Let’s discuss it from two different situations:

1)If the working current of the main circuit is relatively small, we can absolutely adopt the electrical equipment that is used as a relay to the on-off component of main circuit. In other words, considering a contactor as a big sized relay is available;

2)However, if the working current of main circuit is quite large, so is the contactor capacity, which means it flows through large current in its control circuit, but common relay is hardly to realize.