Relays and contactors are two very common electrical components in the field of electrical engineering. Their principles and structures are the same, both utilizing the principle of electromagnets, and their wiring is similar. In industrial settings, they are usually used in conjunction.

The Difference, Wiring, and Comprehensive Application of Relays and Contactors

Relays are primarily used in control circuits, while contactors are mainly used in the main circuit. Therefore, they have the following differences:

1. Size and Contact Capacity: Relays are smaller in size and have smaller contact capacities, generally within 10A. There are also economical relays with capacities within 5A. Contactors, on the other hand, are larger in size, sometimes very large, and since they are mainly used for switching the main circuit, their contact capacities can be very large. This is an important factor in selecting contactors, with contact capacities reaching over 1000A.
2. Coil Specifications: Relay coils mainly come in DC24V and AC220V, with DC24V being the most common. Contactor coils come in various specifications, covering multiple AC and DC options, with AC220V being the most common.
3. Number of Contacts: Relays have fewer contacts, generally divided into two-way and four-way, and cannot be expanded. Contactors are divided into main contacts and auxiliary contacts. The main contacts are used to switch the main circuit and are the primary working circuit of the contactor. Additionally, contactors have auxiliary contacts, similar to relay contacts, usually coming with one normally open or one normally closed contact as standard. These can be expanded if needed.

Generally, PLC outputs drive relays, which then drive contactors, and the contactors control three-phase asynchronous motors. This achieves the separation of high and low voltage circuits.

As shown in the figure above, through PLC programming and the use of relays and contactors, a combination of software and hardware is achieved, allowing low-voltage control of high-voltage circuits.