Difference Between Relay and Contactor
Contactors and relays are vital components in electrical systems, acting as switches to manage power flow. While they share similar basic functions—both being electrically operated switches for load switching—understanding their differences is essential. There are 5 main differences between a contactor and a relay including load capacity, open/closed contact standards, auxiliary contacts, application, and size. Choosing the wrong type for a particular purpose can lead to significant financial losses and damage to the electrical circuit. A thorough grasp of their basic principles and technical distinctions is crucial for making informed decisions in the design and maintenance of electrical systems.
What is a relay?
Relays are the switches that aim at closing and opening the circuits electronically as well as electromechanically. It controls the opening and closing of the circuit contacts of an electronic circuit. When the relay contact is open (NO), the relay isn’t energized with the open contact. However, if it is closed (NC), the relay isn’t energized given the closed contact. However, when energy (electricity or charge) is supplied, the states are prone to change.
What is a contactor?
A contactor is an electromechanical device that regulates electrical current in high-power settings. It consists of three primary parts: a coil, contacts, and a housing. When activated, the coil produces a magnetic field that pulls the contacts together, closing the circuit and enabling current to pass through the electrical load it controls.
Differences between relays and contactors
There are 5 main differences between relays and contactors including load capacity, open/closed contact standards, auxiliary contacts, application, and size.
| Differences |
Relay |
Contactor |
| 1. Load Capacity |
10 amperes or less |
greater than 10 amperes. |
| 2. Open / Closed Contact Standards |
- Operate in both ways including normally open or normally closed as per function demand. - Have a connection or not have a connection with the circuit when triggered. |
- Operate in a normally open configuration. - There is no connection of the contactor with the circuit.
|
| 3. Auxiliary Contacts | Comes with at least two contacts-NC and NO | It consists of at least one set of three-phase power contacts, and built-in auxiliary contacts can also be present. |
| 4. Application | Used in low-power circuits, such as control and signal circuits. | Used in high-power circuits, such as motor or lighting control. |
| 5. Size | Smaller in size, lightweight, and compact. | Larger and bulkier to accommodate higher power handling. |
Applications of Relay and Contactors
Relays are developed to be used in various single-phase networks thus they have single-phase applications while the contactors are developed to be used in three-phase networks. Different kinds of relays are used in different circuits for different applications while some conventional applications of relays are:
- Automotive Applications
- Motor Control
- Industrial Applications
- Controlling Power Loads
Contactors have also different categories and while there are numerous applications of contactors, some common applications are listed below:
- Motor Starters
- Capacitor Banks Switching
- Lighting Control
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Have a question about choosing the right device?
Frequently Asked Questions (FAQ)
1. Can I use a contactor in place of a relay?
While relays and contactors operate on similar theories, they are designed for specific uses in industrial circuits and are not interchangeable.
2. What is the purpose of the contactor?
A contactor is an electrical switch that is designed to open and close a circuit repeatedly. It is typically used in applications that require the switching of higher currents, in contrast to standard relays, which are used for switching lower currents.
3. Do I need a relay or contactor?
It depends on your needs. Relays are used with electrical loads at a range of about 10 amperes or less, while a contactor load capacity is greater than 10 ampere.
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