Because contactors and relays are often rated similarly and intended to do the same type of job in an application, it’s common for people to be confused over the difference between a contactor and a relay.
The main difference between them are the loads that they can handle. Contactors are used for high-voltage loads, high-current loads, or both. Contactors are often used in applications that are passing more than 6A and/or 1.5kV. They have physically larger contacts and are designed specifically to be able to withstand these more demanding loads.
Because contactors are larger and bulkier than relays and have physically larger switch contacts, they consume more power than relays do. If your application doesn’t require a contactor, you can save power by using relays instead.