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.
There are also many
different types of contactors: modular contactors, auxiliary
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.
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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