Contactors and relays are two closely related terms leading to confusions and misinterpretations most of the times. Both of them are electrically operated switches used for control and switching of loads. The basic principle of operation of the
contactor and the relay are the same. The difference between them is in term of their application and where they are used. This article can give you a clear picture of the difference between relays and contactors.
Constructional Features:
Contactors and relays have similar construction. Both have an external envelope to protect all the internal parts from the external environment. An electromagnetic coil is provided for opening and closing of contacts. The contacts are opened and closed by exciting this electromagnetic coil.
Operation of Relays and Contactors
A Contactor is used for switching of motors, capacitors, lights etc, that drains very high current. It has at least a single pair of three-phase input and output contacts. It would be normally open. Some contactors come with additional auxiliary contacts that may be either NO or NC. These auxiliary contacts get activated along with the main contacts. Switching is achieved by energization and De-energization of the contactor coils.
Contactors are chosen upon the ampere ratings of the load. Contactors require an additional supply (either AC or DC depending upon the type of contactor we use) for excitation. It is used for power switching.
A relay consists of at least two contacts and an excitation coil. These contacts may be normally open or normally closed. These contacts are closed or opened by exciting the coil. Relays are used for switching of control circuits and cannot be used for power switching with relatively higher ampacity. It can be used for switching of small lights, sirens, indication lamps etc.
-- Relays are switching devices used in any control circuit for checking a condition or multiplying the number of contacts available.
-- Contactors are switching devices used to control power flow to any load.
Difference between contactors and relays
RELAYS
-- Relays are switching devices used in any control circuit for checking a condition or multiplying the number of contacts available.
-- Relatively smaller in size
-- Used in circuits with lower ampacity. (Max 20A)
-- Mainly used in control and automation circuits, protection --- circuits and for switching small electronic circuits.
-- Consists of at least two NO/NC contacts
-- Relays do not have an arc suppression system built-in.
CONTACTOR
-- Contactors are switching devices used to control power flow to any load.
-- Larger when compared to Relays
-- Used in circuits with low and higher ampacity up to 12500A
-- Used in the switching of motors, capacitors, lights etc.
-- Consists of a minimum one set of three-phase power contacts and in some cases additional auxiliary contacts are also provided.
-- Normally,
contactors have in- built arc chutes for suppression.
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