Contactor is a more suitable choice for applications with motor loads, three-phase circuits, and currents exceeding 15A. Relays are the right choice for signal-level control, low-voltage automation and panels with a current of no more than 10A. How to choose depends on the actual current size of the circuit. The following will be explained one by one from the specification parameters, wiring points and practical application scenarios.
What Are Relay And Contactor?
The loss caused by selecting the wrong switching device is far more than damaging the device itself. Connecting the relay with insufficient rated current to the motor circuit will quickly cause the relay to burn out. Conversely, installing a contactor in a simple signal loop unnecessarily takes up panel space and wastes the budget. The correct choice for the first time can save a lot of subsequent rework.
| Spec | Relay | Contactor |
|---|---|---|
| Typical current rating | Under 10A Electrical relays typically have an ampere rating of less than 10 A and a horsepower rating of less than 0.5 HP | 15A to several hundred amps, some models rated for extreme industrial loads |
| Coil voltage | 5V to 48V DC or AC Relays typically handle lower current levels, often under 10 amps, with coils rated for 5 to 48 volts | 24V to 240V AC or DC, higher coil draw |
| Phase support | Mostly single-phase | Built for three-phase motor and industrial circuits |
| Arc suppression | Minimal or none | Built-in arc chutes or magnetic blowouts |
| Best for | Control panels, alarms, PLC signal switching | Motors, HVAC compressors, pumps, lighting banks |
| Price range | Lower unit cost | Higher unit cost, justified by load handling |
| Best for buyers who | Automate low-power signal paths | Switch heavy motor or three-phase loads |
Relay: Focus on signal-level control
The relay is a compact electromagnetic switch that drives another independent circuit through a low-power control signal. It is small in size, low in power consumption, and especially suitable for low-power scenarios, so it is common in automation panels, alarm systems, and PLC output stages. Because the coil only needs a few volts to trigger the contact, the relay can electrically isolate the precision control electronic components from the driven equipment.
Relay is a more appropriate choice when the current is not large with frequent switching action.
Pros:
- Compact volume, a panel can be installed on dozens of
- The coil has low power consumption and good compatibility with the output interface of PLC or single chip microcomputer
- Rapid response speed in signal-level automation scenarios
- Under the same workmanship, the unit price of relay is lower than the contactor
Cons:
- The upper limit of current is close to 10A, which is not competent for motor or high-power lighting load.
- There is no built-in arc extinguishing structure, and the contact wears quickly when the heavy load is switched frequently.
To learn more details about relay, please read TOMZN’s What Is A Relay Protector?
Contactor: Focus on heavy load
The contactor is an electromagnetic switch designed for industrial-grade current. Its working principle is similar to that of relays, but its load capacity is stronger. The main difference between the two is the load capacity: the contactor is designed for high current loads, while the relay is only suitable for medium and low current scenarios.
Contactors are widely used in motor starters, air conditioning compressors, three-phase switchboards, etc., because these applications require switches to withstand large currents and maintain stable operation.
As long as the load is a motor, compressor, or a three-phase circuit with a current exceeding 15A, the contactor is a more suitable choice.
Pros:
- Withstand high current and three-phase load, do not need to reduce the amount of use
- The built-in arc extinguishing structure prolongs the contact life under repeated switching.
- Modular pole configuration, which can be extended from a single load to the whole distribution panel.
- Sturdy structure, suitable for industrial high frequency use
Cons:
- Larger volume, take up more panel space than the relay
- Higher coil power consumption can not be directly driven by low power PLC output.
To learn more details about contactor, please read TOMZN’s Contactor Buyer Guide.
Relay vs Contactor: What Are Their Differences?
After a preliminary understanding of the two devices, we next compare the relay vs contactor one by one.
Current carrying capacity
The contactors have more advantages: Generally, the rated current of the relay is less than 10A, and the rated horsepower is less than 0.5HP, while the design current of the contactor is much higher than this level.
Volume size
The relays have more advantages: relay can be installed more devices in the control cabinet of the same area due to the compact shell, which is particularly important in the control cabinet with dense wiring.
Arc extinguishing ability
The contactors have more advantages: The built-in arc-extinguishing structure can protect the contacts when the motor is repeatedly switched over under heavy load, and the contacts of general relays will age quickly in this case.
Switching speed
The relays have more advantages. The smaller mass and lower coil power consumption make it respond faster to the control signal.
Applicability of three-phase load scenarios
The contactors have more advantages: Relays are more common in systems with small loads and low requirements, and contactors are designed for industrial scenarios that need to manage large power loads.
Unit price cost
Compared with single device, generally the price of relay is lower, but the total cost of the project still needs to consider the number of devices actually used.
Relay vs Contactor: Respective Unique Features
Relay: Coil isolation protects sensitive electronic components. The relay can completely separate the low-voltage control signal from the switched circuit, thereby protecting the PLC and the microcontroller from the impact of the voltage spike on the load side. It is this isolation characteristic that makes the automation panel usually use relays instead of allowing the control logic to directly connect to heavier switching devices.
Contactor: Modular poles and auxiliary contact expansion. The contactor can usually be equipped with auxiliary contact block and overload relay to integrate a single switching device into a complete set of motor starters. The contactor has a larger volume and a more robust structure because it needs to withstand higher currents and multi-phase loads, and this robust structure also allows modular expansion without redesigning the panel.
Is a contactor just a bigger relay?
It can be understood in this way from the functional point of view, but the structure is not exactly the same. Both rely on the electromagnetic principle to switch the circuit, but the contactor adds an arc extinguishing structure and can withstand a load of more than 15A, while the upper limit of the current of the ordinary relay is usually about 10A.
Can I use a relay instead of a contactor for a motor?
Only a very small horsepower motor can. The rated current of ordinary relays is usually less than 10A, and the rated horsepower is less than 0.5HP. Motor with higher power requires contactor-level switching capability.
What amperage marks the line between relay and contactor?
Most manufacturers set the dividing line between 10A and 15A. The relay generally does not exceed this range, and devices that need to switch heavier loads or three-phase circuits are designed as contactors.
Do contactors need overload protection?
It is needed in most motor circuits. The contactor is responsible for performing the switching action, but it needs to be equipped with a thermal overload relay to provide protection when the motor continues to overcurrent, which is a function that the contactor itself cannot achieve.
Why do relays fail faster in high-current circuits?
Ordinary relays lack the arc extinguishing structure that the contactor has. Repeated switching under high current will cause the contact to wear much faster than the contactor.
Relay vs Contactor: Which One to Choose?
Select Relay to meet any of the following scenarios:
- Load current does not exceed 10A, and is a single-phase circuit.
- Need to switch signals for PLC, alarms, or automation controllers
- Limited space of the control panel, and a compact device
Select Contactor to meet any of the following scenarios:
- Need to start or stop the motor, compressor, water pump
- Three-phase circuit, or the current exceeds 15A
- Frequent load switching requires built-in arc extinguishing protection
If you need a relay product for control panel and voltage protection, you can view the TOMZN Relay product series. If you need modular contactors for motors and three-phase switching, you can view the TOMZN Contactor product range.
