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Difference between Contactors and Relays

Contactors and Relays raise many questions, even among professionals. This article answer defference between Contactors and Relays main questions. The most common questions come about the exact difference between contactor and relay and when to use them.

Contactor and Relay

There are also many different types of contactors: modular contactorsauxiliary contactors, vacuum contactors, motor protection and combination switches. Each will be discussed separately and the differences between the types and the difference in use will become apparent.

Difference between a contactor and a relay

Originally, the term “contactor” was used specifically for a strong and powerful relay. Contactor typically made for 3-phase applications. Where relay more commonly used in single phase applications. The contactor connects 2 poles together without a common circuit between them while a relay has a common contact that connects to a neutral position.
Contactors are electromagnetic switches that can handle higher loads compared to a relay. They are used when a high voltage must be switched (230V / 400V) in power applications. The similarity between relays and contactors is that they are both used in controls. Contactors are controlled remotely. They have 2 switching positions (in normal applications they switch monostable). Contrary to relays, contactors always have 2 interruptions per contact. The reason for this is mainly safety and wear.

Relay with base

Construction of Contactors

The construction of a contactor is quickly explained. It consists of a housing, electrical connections, a magnetic coil, a fixed core coil, a movable core, switching contacts and a spring system to open the contacts.
A distinction is made between models with power contacts and models with auxiliary contacts. The different models can be identified by the numbers on the contactor.

Models with power contacts

If it has single digit numbers (1-6) it is a model with power contacts. These are used to switch motors or lights). Power contacts, also called main contacts, always start with number 1.
This means that the first contact has numbers 1 and 2, the second contact has numbers 3 and 4 and so on....

What is the reason for this numbering?

As a rule, the power supply is connected to the odd numbers and the consumer to the even numbers. This makes it easy to maintain an overview of complex circuits or circuits that have been in service for years.
Model with Auxiliary contacts
Two-digit numbers (13, 14,…) indicate a model with auxiliary contacts. These are used in industrial controls, for example. Auxiliary contacts, also called control contacts, each have a sequence number and a function number. The first number continues (sequence number) and the second number indicates the type of contact (function number).

Operation of Contactors

Contactors will always - within milliseconds - open the normally closed contacts before closing the open contacts. Another feature is the so-called "spark chamber". This is where the sparks that occur during gear shifting are extinguished to prevent wear.

Maintenance of Contactors

In general with contactor, it is the contacts that usually require maintenance. With auxiliary relays, maintenance is limited because they switch only low powers. With contactors, the contacts are best regularly inspected, maintained and replaced if necessary. This is because the contacts will gradually weak so that correct operation cannot longer be guaranteed. This obviously depends on how often the switching on and off takes place.

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jithesh said…
Nicely expalined