Contactors and relays are electric switches used to facilitate the connection and disconnection of electric circuits. Despite being used for somewhat similar purposes, there are several distinguishing attributes between the two. For understanding contactors and relays, let’s briefly overview both working mechanisms.
Explain The Difference Between Contactors And Relays
How Do Contactors And Relays Work?
The contactors use a magnetic field generated by an electromagnet and eventually move the armatures, resulting in the circuit opening or closing accordingly. Contactors are meant to handle high currents and heavy loads like motors, lighting or heating systems.
A relay uses current to energize the coil in the relay and create a magnetic field, which is used to open or close the circuit. Relays are used for handling low currents, such as in small-scale lighting systems, safety devices, air conditioners, and other home appliances.
Relays VS Contactors
Contactors And Relays Types
Based on their functions and mechanisms, there are several types of relay and contactor, out of which the most common ones used are:
1. Types Of Contactors
- Modular Contactor(AC and DC)
- Knife-switch contactor
- Manual contactor
- Vacuum contactor
- Electromagnetic contactors
- Reversing contactors
2. Types Of Relay
- General purpose relay
- Electromagnetic relay
- Solid state relay
- Step relay
- Differential relay
- Impulse relay
- Timer relay
Types of Relays
Difference Between Relay And Contactor
While the contactor and the relay are used for similar purposes, why are they different products? Let’s elaborate on the features based on which there is said to be a difference between contactors and relays.
Contactors and Relays – Know the Difference and Applications
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Purpose Of Installation
The purpose of installing contactors and relays in electrical systems is to ensure smooth operations with a minimum risk of damage. A contactor is installed to deal with high currents, while the relay is used for opening and closing circuits with low power. The Contactor and relay keep the circuits and equipment safe from damage. They are installed in places with the electrical setup to control devices and equipment.
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Difference In Load Capacity
Relays are usually compatible enough to tolerate loads of 10 A or even less, which makes them suitable for low-power usage circuits. On the other hand, a contactor can carry a load as heavy as 10A to 1000A or even greater than it. And that is why the contactors are the perfect choice for high-power circuits.
Wiring Diagram of Contactors
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Different Open/Close Contact Standard
It indicates the default state of the contactor and relay. A contactor is normally open (NO) in its default stage, and there is no current flow in that state. In comparison, a relay in its de-energised state can be Normally Open or Normally Closed, depending on the usage.
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Difference In Size
The size of a contactor is more extensive than that of a relay, which is small. The bigger size of the contactor is rightly justified by its capacity to handle higher loads. Similarly, the lower capacity of a relay is correlated to its smaller size.
Wiring Diagram of Relay
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Durability And Longevity
The former wins the argument when the contactor and relay are compared concerning durability. The contactor is built in a way that it can tolerate larger loads for extended periods than a relay. You can switch contactors frequently millions of times without fear of any damage or malfunction. In contrast, a relay can entertain the switching less frequently and only upto a few thousand times.
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Auxiliary Contacts
Contactors often come with attached auxiliary contacts. They can either be NO or NC. They are responsible for controlling the contactor and providing additional signals. An example of such contact is any indicator light when the motor is operational. Whereas, often, a relay doesn’t have any auxiliary contacts attached.
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Consumption Of Power
The contactor needs more power due to the bigger electromagnet and coil used, while the relay needs less power as there is no coil or smaller electromagnet.
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Cost Factor
When using contactors and relays, the contactors need you to pay more when compared with relays. The increased price is justified by the level of protection and automation that contactors provide.
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Switching Speed
The switching speed of a contactor or relay is the time it takes to switch positions, from open to close or vice versa. The contactor takes around 20 to milliseconds to switch, while a relay is quicker and takes around 3 to 100 milliseconds. It is because contactors are by-built made to carry heavier loads and are slightly slow in switching, but relays are meant for lighter loads, and that is why they take less time to switch.
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Safety Measurements
Due to the high capacity of the contactors to bear loads, the safety measurements they are equipped with are also higher than those of the relays. The safety level is acquired via these techniques:
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Spring Loaded Contacts
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The contactor disconnects the circuit completely in a de-energized state without any current passing. The springs keep the contacts apart because they are welded together. If the circuit isn’t opened properly in an overload situation, there could be a safety risk.
This feature isn’t necessary in relays since they specialize in lower current loads.
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Arc Suppression
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This feature is made a part of contactors as they have to carry higher than 10 amperes of load. Arc separation involves breaking up the current waves, which still try to flow when the contacts are separated.
This feature is uncommon in relays as they dont need that much safety against higher currents. The allowed load in a relay is less than 10 amperes, so there’s no need for additional safety features.
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Overload Safety Feature
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The feature interrupts the circuit if there is an increased current flow during a preset selected time, usually 10-30 seconds. This, in turn, provides additional protection to the equipment.
In the case of relays, this feature is generally not present.
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Applications
Contacts are made keeping in requirements for a 3-phase system. For relays, the standard is set for a single-phase system. A contactor can withstand voltage up to 1000 volts, as opposed to a relay that can tolerate only 250 volts.
After delving into the differences between contactors and relays, we can gain a more intuitive understanding by watching a video. This video provides a detailed explanation of the basic construction of contactors and relays, as well as their practical applications in various electrical systems. By watching the video, you will be able to understand more clearly how these devices perform their crucial functions in circuits. Please click the following link to watch the video:
Source: @ElectricianU on YouTube
How To Make A Choice Between Relay And Contactors
The choice between relay and contactor is not based on personal preference but on several factors based on relay and contactor differences. The foremost of them is the purpose of use. You must know the type of load and current rating for that particular circuit for which the type of switch is to be used.
The frequency of switching operations is also a key point in this respect. One must know that circuits with heavy loads, high control voltage, and frequent switching will work well with a contactor. Similarly, a relay suits circuits with low power, lower control voltage and less frequent switching.
Contactor Vs Relay Vs Circuit Breaker
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Points Of Difference |
Contactors | Relay |
Circuit Breaker |
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Primary Function |
Used for connecting/disconnecting high-power loads | Used for low circuit loads | |
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Load Capacity |
10A to 1000A or even greater | 10 A or even less | 15A to 20A |
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Manual Or Electric Control |
Electric control | Electric control |
Manual as well as electric control |
| Durability | More durable | Less durable |
More durable |
| Contact Type | NO, and NC | NO, and NC |
NC only |
| Switching Speed | Slow | Fast |
Fastest |
Frequently Asked Questions
1. What Are The Two Types Of Armatures Used In Contactors And Relays?
Armatures are one of the main components of relays and contactors. They are movable parts that move when the coil is energised, thus opening or closing the switch. Sliding and swinging armatures are the two types used in contactors and relays.
2. Contactors Are Always NC And Relays Are Always No. Is That True?
No, it is not valid. Both relay and contours can have normally open (NO) or normally closed (NC) contacts, depending on the nature of use and intended device.
3. What Is The Contactor Relay Price?
Depending on the model type or load capacity, the contact will cost around USD 4 to USD 10. Meanwhile, the price of a relay ranges from USD 2 to USD 7 and may vary accordingly. It must also be noted that bulk purchases can further cause the prices to drop.
Final Words
Contactor and relay are both essential devices for your electrical system, provided they are somewhat different despite being working as an electrical switch. They differ with respect to their capacity, mechanism and working and based on these features, have their peculiar installation areas.
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