Contactors and Contactor Relays – Upgrading Your Electrical System
Published on : Tuesday 31-10-2023
ABB offers a comprehensive selection of contactors for simple and extreme application as well as products with specific purposes.
Contactors and relays are essential components in electrical systems, serving as switches for controlling power flow. Both devices share similarities in their basic function.
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.
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, switching points and a control spring.
How do they work?
A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it)
As contactors are used for high-current load applications they are designed to control and reduce the arc produced when the heavy motor currents are interrupted. Other than the low current contacts, they are also set up with Normally Open contacts. These are devices which handle more than 20 Amperes current and over 100 kiloWatts power.
The contactor has an AC/DC supply driven coil input. This will depend on the requirement. This coil will mostly be controlled by a lower voltage PLC. They can also be controlled by the motor voltage. The motor may have a series of coils connected to either control the acceleration or even the resistance.
When current is passed through the contactor, the electromagnet starts to build up, producing a magnetic field. Thus the core of the contactor starts to wind up. This process helps in energising the moving contact. Thus the moving and fixed contacts make a short circuit. Thus the current is passed through them to the next circuit. The armature coil brings in high current in the initial position. This reduces as soon as the metal core enters the coil. When the current is stopped, the coil gets de-energised and thus the contacts get open circuited.
The difference between contactors and relays
There are several differences among relays and contactors, however, some basic and common differences among them are discussed below:
1. Load capacity: the first difference among a relay and contactor is that both have different load capacities. Relays are used with electrical loads at a range of about 10 amperes or less, while a contactor load capacity is greater than 10 amperes.
2. Open/closed contact standards: the second differences are that relays are designed to operate in both ways, i.e., in normally open or normally closed as per function demand.
Contactors are designed to operate in a normally open configuration. This can be summarised as when the contactor is triggered there is no connection of contactor with circuit when triggered as per the configuration of the relay in a circuit.
3. Auxiliary contacts: in contactors, auxiliary contacts are used to perform a different function that is linked to controlling the contactor. Auxiliary contacts for a contactor can be normally open or normally closed as per requirement.
4. Safety features: the safety features in relays and contactors are different as per the power of each device. Spring-loaded contacts are used to ensure that the circuit is tripped or opened in case of any over-circuit condition to reduce or prevent damage to electrical devices. Relays are used in circuits that have load capacity equal to or smaller than 10 amperes, so spring load contacts are not commonly seen in relays due to their low load capacity.
On the other hand, contactors have load capacities greater than 10 amperes which means that they can carry higher loads. As higher loads are carried by contactors, spring-loaded contacts are used to ensure the circuit is broken when it is de-energised due to an overload condition. In circuits that have higher loads, the contacts of contactors are welded together, and it can result in a dangerous scenario as in case of an overload condition the circuit will not be opened to eliminate this scenario spring-loaded contacts are using.
5. Multiple circuits: electrical contactors are only used to control a single main load circuit, either 1-phase or 3-phase. However, while electrical relays can also control a single main circuit, they can also be used to control multiple main circuits by relaying information to each.
Advantages of contactors and relays
i. It is a fast switching operation
ii. It is simple in construction
iii. It provides protection
iv. Lower power consumption
v. High load capacity
vi. It is suitable for both AC and DC devices
vii. Fast switching
Applications of relay and contactors
Relays are developed to be used in various single-phase networks thus they have single-phase applications while the contactors are developed to be used in three-phase networks. Different kinds of relays are used in different circuits for different applications while some conventional applications of relays are:
i. Automotive applications
ii. Motor Control
iii. Industrial applications, and
iv. Controlling power loads
Contactors have also different categories and while there are numerous applications of contactors, some common applications are listed below:
i. Motor starters
ii. Capacitor banks switching, and
iii. Lighting control.
Durga Mechatronics has been associated with ABB for the last 3 years for low voltage electrification products.