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Contactor vs. Relay: A Detailed Comparison

Switch circuits that have high isolation are a necessity in many electrical applications. These circuits require the switching of high currents and voltages, and in some cases, using semiconductors isn’t efficient. In such cases, engineers have to select between contactors and electromagnetic relays. This article will highlight the significant difference between relays and contactors. Both use electrical switches for switching and control of the loads. Contactor vs. Relay usually confuses a lot of people due to their closeness. 

Introduction to Contactor vs. Relay

Electrical relay

Image 1: Electrical relay

Contactor vs. Relay: Definition

A relay is a device that operates so that we keep altering contacts in one electrical circuit. We achieve the alteration by triggering changes in the same circuit or by two or more related courses. 

In contrast, a contractor is a device that consistently creates and interrupts an electrical circuit in a typical environment. 

Contactor vs. Relay: Working Principle

Both relays and contactors use electromagnetic solenoids to create one or several pairs of contacts. They achieve this via the closing and opening of contacts. 

Constructional Features

Engineers construct these devices similarly. One common thing is that they always have an external casing that protects the internal parts from external hazards. 

We use contactors to create capacitors, motors, etc., that consume much power. Thus, it usually consists of at least one pair of three-phase output and input contacts. And it’s usually open.

Contactor Wiring wok

Image 2: Contactor Wiring wok

Other contractors may come with extra auxiliary contacts that are either Normally Closed or Normally Open. The primary contacts and the additional contacts become active simultaneously. You’ll achieve switching via energizing and de-energizing the contact coils.

When selecting contacts, you should mainly consider the load’s ampere ratings. Also, note that you should supply contactors with additional power. 

It can either be DC or AC, depending on the type of contractor you have. We use the extra power for excitation and to enable power switching.

Relays are made up of a contactor coil and at least two contacts. To open or close the contacts, you should excite the wave.

Operating

A relay operates depending on the change of current in a specific circuit. It utterly depends on how it’s configured. If there’s an overload, it will cause the relay’s electromagnetic armature to close or open. 

A contactor operates in a similar way to a relay. If there’s an overload in the circuit, it causes the electromagnet to energize, creating a magnetic field. The magnetic field triggers the armature to open hence cutting power flow.

Comparison of Contactor vs. Relay

Size

Contactors are relatively more extensive when compared to relays. Therefore, contractors carry more load than control relays.

Contactor vs. Relay: Load Capacity

Contactors are usually optimized to carry electrical loads above 10A. In comparison, control relays can only carry up to a maximum of 10A. 

That’s why you’ll typically find control relays operating in single-phase circuits. On the other hand, contractors can efficiently work in a three-phase course.

Contacts

Contactors usually have at least three primary electrical contacts and extra in-built contacts.

In comparison, a control relay usually comes with two NC or NO types of electrical contacts. In addition, you’ll find that control relays operate in closed and open communications. As for contractors, they work well with genuine connections. 

Contactor vs. Relay: Arc Suspension

Since relays work with relatively lesser voltages, there isn’t any concern about the arc. In comparison, contactors display arc suspension. 

It acts as a preventive measure against any damage to the device. 

Open/Closed Contact Standards

Engineers create contractors so that they can operate on Normally Open contacts. We connect contactors’ connections to spring to ensure a better and safer switching. In comparison, engineers optimize relays to work effectively on Normally Closed or Open contacts.

Safety Features (Spring-Loaded Contacts)

Since contractors deal with higher loads, they usually have extra safety features. For example, you’ll find springs on the contacts to ensure that the circuit is broken in the event of a power outage.

Since relays deal with much lesser power, they usually don’t have strings attached.

Safety Features (Arc Suppression)

It is another common feature that you’ll find on contactors as a measure to regulate high loads. On the other hand, engineers are less concerned about having arc suppression on relays since they deal with less power.

Safety Features (Overloads)

Another essential safety measure is the presence of overloads on contactors. These serve to interrupt the circuit if the current goes past a set limit for a specific period. The time usually ranges between 10 and 30 seconds.

By doing so, we ensure that we protect downstream electrical components from damage due to excessive power. Like other protection features, overloads are not so popular on relays.

Contactor vs. Relay: Control System

Image 3: Control System

Contactor vs. Relay: Switching Speed

We measure actuation time from applying the power to the coil to when the contacts settle. On average, relays have a switching speed between three and 100 ms. As for contractors, they have a switching speed within the range of 20 and 250 ms.

Contactor vs. Relay: Long lifespan

Relays last much longer compared to contractors when it comes to lifespan. Relays have a lifespan of approximately 10⁷ cycles. On the other hand, contractors have a lifespan of roughly 10⁵ cycles.

Contactor vs. Relay Applications

Contactor vs. Relay: Electric heater

Image 4: Electric heater

In typical cases, we use contactors to control electrical components such as heaters, lighting, and motors. We use them in applications with continuous supply and interruption of electrical power. 

On the other hand, we use relays in low-power circuits such as timing and signaling. Contactors are not suitable for signal switching due to their limited isolation and massive size. In brief, contactors are mainly used in primary circuits, while relays are applied in auxiliary circuits.

How to choose Contactor vs. Relay for your application

When choosing between contactors and relays, we recommend applying the following rules:

Contactor vs. Relay: When to Use a Contactor

  1. One-phase or three-phase
  2. Current equal to or above 9A
  3. It can take up to 1000VAC
Contactor vs. Relay: Power Source

Image 5: Power Source

Contactor vs. Relay: When to Use a Relay

  1. One-phase
  2. Below 10A
  3. It can take up to 250VAC

We always recommend analyzing the item’s features that you want to use before purchasing it. Even better, you should consult a licensed electrician to ensure you make the proper selection.

Conclusion

Contactors and relays are very efficient when used for switching electrical power. To achieve this, you must select the correct voltage and have the appropriate contact size. The selection you make will depend on the job you want to do. Relays come in many forms, while contractors are more standardized.

That’s it on contractors and relays. If you have any queries, you can always reach our contact page.

Hommer Zhao
Hi, I am Hommer, the founder of WellPCB. So far, we have more than 4,000 customers worldwide. If you have any questions, you can feel free to contact me. I really appreciate any help you can provide.

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