Main Difference – Contactors vs. Relays
Contactors and relays are used to turn on or off different parts of circuits. The main difference between contactors and relays is that relays are used with small currents whereas contactors are used when the currents are large.
What are Relays
Relays are components in electric circuits which are used as a switch. Typically, relays consist of an electromagnet and three contacts. When the electromagnet is switched off, the “common” contact is touching the normally closed contact. When the electromagnet is switched on, the common contact gets attracted by the electromagnet. This attraction causes the common contact to move towards the electromagnet, leaving the normally closed contact. The third contact is between the electromagnet and the common contact, so as the common contact tries to move towards the electromagnet, it meets this third contact. This contact is called the normally open contact.
So long as the electromagnet is on, the common contact remains in touch with the normally open contact. When the electromagnet is switched off, however, the common contact moves back to its original position to touch the normally closed contact once again. The normally open and normally closed contacts can be connected to two different outer circuits so that the position of the common contact determines which outer circuit is switched on. How a relay works in this way is explained in the video below:
Circuit symbol for a relay
What are Contactors
Contactors work in much the same way as relays do. They also consist of electromagnets that can be switched on and off, which in turn determine how the different terminals are connected. The working principle of contactors and relays is the same; however, contactors can handle much larger currents. Contactors are usually bulkier than relays, and they could be specially designed to work with 3-phase AC currents.
A contactor
Difference Between Contactors and Relays
Current Capacity:
Contactors are used with large currents.
Relays are used with smaller currents.
Size:
Contactors are bulkier and noisier than relays.
Uses:
Contactors are used in power circuits.
Relays are used in control circuits.
Image Courtesy:
“Difference Between Current Transformer and Potential Transformer” by Iainf, Moxfyre and FDominec et al. [Public Domain], via Wikimedia Commons
“Contactor mounted onto DIN rail” by Kae (Own work) [CC BY-SA 3.0], via Wikimedia Commons
