Both relays and contactors are electromagnetic switches designed with the aim to provide switching and controlling the action. The significant difference between relays and contactors lies in the loads they carry and the power utilization factor. Basically, relays are suitable for low voltage or current applications. As against, the rated value of voltage and current in the case of contactors is comparatively high.
Both relays and contactors are switches that are operated electrically for the purpose of load switching and circuit controlling. Generally, the load current rating offered by relays is around 20A while the contactors support load current rating of even 30, 40, or 50A.
Content: Relay Vs Contactor
Comparison chart
| Basis for Comparison | Relay | Contactor |
|---|---|---|
| Purpose | Low voltage switching | High voltage switching |
| Device size | Small | Comparatively large |
| Cost | Inexpensive | Expensive |
| Power Consumption | Less | Comparatively more |
| Circuit suitability | Control circuits | Main circuits (control and power circuits) |
| Load current capacity | 10A or less | More than 10A. |
| Voltage rating | Up to 250V | Up to 1000V |
| Switching speed | Fast | Comparatively slow |
| Overload connection | Not permitted | Permitted |
| Safety measure | Less | More |
| Number of controllable loads | Typically 2 or 3 | Generally 4 but is expandable. |
| Contact type | Either NO/NC depending on the operation. | Typically NO |
| Coil changing facility | Not exist | Generally exist |
| Applications | Motor control, electric pumps, etc. | Transformers, induction motor, capacitor banks, magnetic starter, etc. |
Definition of Relay
Relays are switches designed to operate electrically and used for controlling the circuits by using low power signals. It acts as a link between the circuit that is needed to be controlled and the circuits which control it. By the use of relays, electrical isolation between controlling and controlled circuits is maintained.
A relay operates in a way that it has two sides namely primary and secondary. There is a coil present in the primary side which is energized by a low-power dc supply which is nothing other than the control signal. While the secondary side forms a connection with the load which is required to be controlled. This load is generally AC in nature like a fan, pump, bulb, compressor, etc.
The electromagnetic coil generates a magnetic field when the current passes through it. With the help of spring, an armature is connected to the end of the coil and this armature is attracted towards the coil when the supply energizes the coil. When the coil is de-energized then the armature attains its normal position. In this way the circuit gets complete and the load experiences the supplied electrical energy and operates accordingly.
Definition of Contactor
An electrical device designed with the aim to turn on or off an electrical switch is known as a contactor. Power-consuming devices are controlled by contactors offering heavy-duty contacts so as to provide safe power circuit switching.
Similar to the operation of relays, contactors are controlled by the coil (solenoid) after being energized by an AC source. However, unlike relays, it has an arc suppressing cover to provide quenching to the arc formed under open contacts condition with the load. In contactors, due to the upward attraction of the armature, the moving contact forms a connection with the stationary contact. However, after de-energization, the dropping out of the armature disconnects the moving contact and the stationary contact.
It is to be noted here that in the open condition of the magnet (armature), a large air gap exists, thus reactance is low. After the coil gets energized, it draws a large amount of current due to which armature gets closed thereby reducing the air gap. This increases the reactance and reduces the coil current. In this case, the coil current drops to magnetizing current which holds the contactor closed against the force applied by the spring.
Key Differences Between Relay and Contactor
- The key factor of differentiation between relays and contactors lies in the sole purpose of their use. Relays are generally suitable for low voltage switching applications while contactors are used for high voltage switching applications.
- The overall size of relays is small in comparison to contactors. While despite their small size, relays are heavier in comparison to contactors.
- The electromagnets used in relays are comparatively smaller in size than the one used in contactors thus relays consumes less power in comparison to contactors.
- Contactors are quite expensive than relays.
- The presence of relays is suitable in control circuits, for single-phase loads. However, contactors exist in the main circuit for control and power applications, for three-phase loads.
- The loads in relays are designed to handle the current of about 10 A or less while loads in contactors can handle current more than 10 A up to 30, 40, or 50 A.
- The voltage ratings offered by relays are up to 250 V whereas that of contactors is around 1000 V.
- Relays offer comparatively faster switching speed than contactors for the same application.
- Relays are designed to control 2 or 3 loads whereas contactors generally control 4 loads moreover contactors offer load expandability up to 6, 8, or even 12 loads.
- It is said that contactors offer better safety than relays during operation due to the fact that the safety components like arc suppression system and spring contacts are built-in within the contactor however are absent within the relays.
- In relays connected to the overloads, in general, is not provided whereas overload connection does exist in the case of contactors to deal with excess power consumption.
- In relays, there are no chances of changing the coil within it whenever required while most of the contactors support the change of coil as and when required.
- Relays support both normally open or normally closed contact depending on the conditions whereas contactors generally designed to operate under normally open contacts.
Conclusion
Hence, we can say relays suit single-phase applications thus are used in automation and protection circuits like in motor control, electric pumps, etc. While contactors suit three-phase applications so are useful in induction motors, transformer, capacitor banks, etc.