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Difference between Contactor and Relay
Contactor and relay are both electromagnetic switches that are designed to provide switching and controlling functions in the electric circuits. The primary function of both relay and contactor is similar, but there are many differences between them that are listed in the table below.
The major difference between these two devices is that a relay is suitable for voltage and current applications, whereas a contactor is suitable for high voltage and current applications. Relays and contactors are both switches which are operated electrically for providing switching and controlling of the circuit.
This article will provide all the noticeable differences between a contactor and a relay. Also, a short description of both contactor and relay is added to help the readers understand the differences better.
What is a Contactor?
A contactor is an electromagnetic switch which is designed to make or break the connection between the electric power supply and the load. In practice, the contactors are mainly used to control the high power-consuming devices because they offer heavy-duty contacts so as to provide safe switching of power circuits.
The operation of a contactor is controlled by a coil (called solenoid) which is energies by an AC source of power. The contactor also consists of an arc suppressing cover that is provided to quench the arc formed during the operation of the contactor.
contactor consists of several contacts depending upon the type of load and application. In general, these contacts are normally open (NO) contacts, hence the load being disconnected from the power supply when the coil of the contactor is de-energized. However, a contactor can also be designed for both NO (Normally Open) and NC (Normally Closed) contacts.
Some common applications of contactors are in the starters used for switching ON and OFF the electrical devices like motors, lights, etc.
What is a Relay?
A relay is a simple electromagnetic switch which makes or breaks the electric connection between the power supply and the load. A typical relay uses an electric signal to control an electromagnet, which operates the armature of the relay for making or breaking the connection.
The main parts of a relay include an electromagnet, movable contact (armature), switching points and a control spring. The operation of the relay is based on the electromagnetic induction. When an electric supply is given to the coil of electromagnet, it produces a magnetic field around it which attracts the movable contact and closes the switching points. In this way, a relay makes the connection between two circuits. When the supply to the electromagnet is removed, the armature comes back to its original position under the force of control spring and breaking the connection between the circuits.
Relays are widely used in various electrical and electronic systems for switching operation. Relays are also used to protect the electrical system, as they can detect and isolate the faults in the electrical power transmission and distribution systems. Also, relays are used to control a high current circuit with the help of a low current signal such as in starter solenoid in automobiles.
Differences between Contactor and Relay
As it is evident, the definitions and functions (switching a circuit) of both the devices are similar enough and they do not help us to understand the differences between them. Therefore, in the following table, we have differentiated a contactor from a relay by considering various parameters.
| Parameter | Contactor | Relay |
|---|---|---|
| Definition | A contactor is an electrically operated switch which is designed to make or break the electrical power circuits. | A relay is an electromagnetic switch that is designed to operate electrically and used for switching the circuits by using low power signals. |
| Purpose | The switching of high voltage and current circuits is the main purpose of contactors. | The switching of low voltage and current circuits is the purpose of relays. |
| Circuit symbol |  |  |
| Load capacity | The contactors are generally used for the switching of loads greater than 10 A. | The relays are generally used for switching of the loads of 10 A or less. |
| Voltage rating | Contactors are rated up to 1000 V. | The voltage ratings of relays are up to 250 V. |
| Power consumption | The size of electromagnet used in a contactor is large, thus it consumes more power. | The size of electromagnet used in a relay is relatively smaller in size, thus it requires less power to energize than a contactor. |
| Open & close contactor standards | Contactors are mostly designed to operate with normally open (NO) contacts. Thus, when the electromagnet of contactor is de-energized there is no connection. | Relays are commonly designed to have both normally open (NO) and normally closed (NC) contacts depending upon the application. |
| Auxiliary contacts | Contactors are often fitted with some auxiliary contacts that can be NO or NC. However, the auxiliary contacts are provided to perform additional functions related to control of the contactor. | A typical relay does not have any auxiliary contacts. |
| Switching speed | For the same application, the switching speed of a contactor is slow. | The switching speed of a relay is relatively more. |
| Suitability | Contactors are suitable for switching of both control and power circuits. | Relay is suitable for control circuits only. |
| Size | The physical size of a contactor is relatively larger. | The size of a relay is smaller than a contactor. |
| Spring loaded contacts | As contactors are used for switching high power loads, thus they should contain spring loaded contacts to ensure the circuit is broken when de-energized to provide additional safety. | The use of spring loaded contacts is much less common in relays because they are used in low power switching applications. |
| Arc suppression | Arc suppression is provided in contactors because they carry high power loads. | As the relays are not designed for high power applications, thus the arcing is not a concern and hence, the arc suppression feature is commonly not used in relays. |
| Overload safety | Overload safety is provided in contactors that interrupts the circuit if the current exceeds a set threshold for a selected period of time (usually 10 to 30 seconds). This helps to protect the equipment from damages due to high currents. | The overload safety is not generally provided in case of relays. |
| Safety | Contactors provide more safety measure in the circuit. | Relays provides less safety to the circuit. |
| Cost | Contactors are expensive devices. | Relays are less expensive than contactors. |
| Applications | Contactors can be used for switching of 1-phase as well as 3-phase loads such as motor power circuits, motor starters, switching circuit of capacitor banks, magnetic starters, etc. | The relays are mostly used in control circuits of single phase loads such as protection systems, control circuit of circuit breakers, motor control circuits, etc. |
Conclusion
Both Contactors and Relays perform similar function of switching of circuits. The significant differences between contactor and relay are listed in the above table. However, the major difference between the two devices is that a contactor is used for controlling and switching of loads more than 10A, whereas a relay is used for switching and controlling of loads less than 10A.
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