How Do We Differentiate a Contactor from Other Relays?
Contactors can be described as a special-purpose type of relay that are intended for interrupting and establishing high-power circuits repeatedly. Contactors commonly have multiple contacts that are normally open, so that load power is shut off when coil is disconnected to power source. Contactors are switching devices for auxiliary and control circuits and are used to interlock, control and provide signals to switchgear panels as well as switching devices. Reasonably, the most frequent industrial use for contactors is for electric motors. Most of the integral horsepower motors, that are 1hp and above, are controlled with contactors.
A contactor is a magnetically-operated device often used to control power that is above 5kW while the term “relay” is commonly associated with power below 5kW. A contactor can be a relay but a relay cannot be a contactor.
Relay Vs. Contactor
Relay
Goes “Click” when energized.
Switches loads of lower wattage
Applications include control circuitry
Generally switches currents less than 10-15 Amperes.
Generally switches voltages less than 240 VAC
Switches AC or DC
Not normally rated in horsepower.
Double throw is typical (normally open and normally closed contacts in one unit).
Relay coils are AC or DC, but tend to be 5-24VDC with back emf power diodes to protect relay control electronics.
The buck just gets passed here. Relays tend to be "pilot" control devices, controlling more powerful contactors.
Contactor
Goes “Clunk” when energized.
Switches loads of higher wattage
Applications include power circuits (from electric motors to a country's main power grids).
Generally switch currents above 10-15 Amperes.
Generally switch voltages 120 VAC or greater.
Switch AC or DC, resistive or inductive loads, but generally switch AC Loads.
Usually includes a horsepower rating.
Single throw is the norm (either normally open or normally closed contacts, rarely both).
Usually A.C. powered coils (24 VAC for safety- interlocked with EPO or EMO, and Panel open interlock switches; 120-240VAC for simplified operations are typical applications)
The buck stops here. Contactors are the real deal. They can be controlled by smaller, less powerful relays.
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