Today is...
Friday, December 19, 2014
Welcome to, the global online
community of automation professionals.
Featured Video...
Featured Video
A quick introduction to EtherCAT for motion control and I/O...
Our Advertisers
Help keep our servers running...
Patronize our advertisers!
Visit our Post Archive
contactor or relay?
basic differences between contactor and relay?

what is the basic differences between contactor and relay and why can't we use the contactor instead of relay and vice versa?

0 out of 1 members thought this post was helpful...

Simply, a relay is cheaper than a contactor - generally. A contactor is used for a higher load. For example, we have pump control applications where the electronics control a relay and the relay controls the contactor which starts the pump.

Also - the relay load to the electronics is lighter where the contactor may draw heavy amps and produce a bigger arc potential when it fires.

Bob Hogg

By Gireesh Gokuldas on 16 September, 2012 - 7:33 am

Thanks Mr.Bobb,

its just now my superior asked me this simple question. actually i was not aware of this thing. for me it was both same. so now you helped me to answer his question in a proper way. once again thanks and do upload things like this.

Gireesh Gokuldas

1 out of 1 members thought this post was helpful...

Responding to Anonymous' Feb 5, queries... the following discussion applies to only electrically operated devices:

IEEE Definition
Std 100-1992 "Standard Dictionary of Electrical and Electronic Terms" (Std 100-1992) has many definitions for 'Relay'! Conversely, the Standard's only 'Contactor' definition calls it a 'Load-Switch'! The point is that there is no simple definition.

Historical Perspective
In 1905 'relay' and 'contactor' were defined by the AIEE (predecessor of today's IEEE) as follows:

A device... by which contacts in one circuit are operated by a change in conditions in the same circuit or in one or more associated circuits.

A device... for repeatedly establishing and interrupting an electric power circuit.

Now, in response to your "difference" question... the terms are delineated by the power they must carry. Here are definitions presented in Struthers-Dunn "Relay Engineering" manual (ca 1945):

An electrically controlled device that opens and closes electrical contacts to effect the operation of other devices in the same or another circuit.

A magnetically-operated device, for repeatedly establishing and interrupting an electrical power circuit. It is usually applied to devices controlling power above 5kW, whereas the term 'relay' is ordinarily employed below 5kW. The terms are often used interchangeably.

Phil Corso, PE {Boca Raton, FL, USA}
[] (

By Steve Myres on 8 February, 2005 - 10:21 pm

Size. Actually, "contactor" is just a trade name for a type of relay used for power switching, and is sometimes referred to as such. Like any other relay, it should be used within its limits with due consideration given to the application specifics such as switching frequency.
Steve Myres, PE
Automation Solutions
(480) 813-1145

1 out of 1 members thought this post was helpful...

relay is for control logic. Contactor is for outputs. However, relays can also be used for low-load outputs.



A contactor is a contactor a relay is a relay.

Ya You are very right ...Relay is relay and contactor is contactor... I fully agree with you...

Ans:- there is no such a difference between Relya and contactor as I know. So as a conclusion Relay is relay and contactor is contactor. And relay can be contactor and contactor can be relay.

Ans:- there is a difference between relay and contactor. relay is used in control circuit only but contactor is used in both control and power circuit.

a contactor can be relay but a relay cannot be a contactor.

By amit shekhar sharma on 4 August, 2007 - 1:01 pm

Ans. contactor is a heavy duty switch whereas the relay is light duty switch

contactor has a hold on contact whereas relay has no such provision

How about the speed of operation? Any difference between the operating time of relay & contactor relay?

By Curt Wuollet on 22 September, 2007 - 6:37 pm

As a rule, contactors are a little slower than relays because the armature is more massive. But there will be overlap as there are slow relays and fast contactors. If you don't mind supplying the current, contactors can be made very fast. I've seen some where the actuation was so fast and positive it sounded like someone smacked the panel with a hammer.

And there are even ballistic contactors made to actuate so quickly that they make contact before the HV they switch has a chance to ionize the air and arc. So it's hard to generalize. Smaller will almost always be faster. We used some tiny reed relays on test equipment that were almost as fast as garden variety transistors.


By Laban Waweru on 13 June, 2008 - 6:52 pm

I think you are all mistaken, We have a contactor relay which is used in switchgears, a Relay used in control systems.

hey man i build and test air circuit breakers which have heavy duty springs which close and open the circuits to bus-bars and they're fn loud too especially 4000a and up

>contactor has a hold on contact whereas relay has no such provision <

Hold on contact is something that can be applied to either component. If anything, it would more apply to the relay than the contactor because the hold is a smaller voltage to keep the coil engaged than what a contactor passes through. Once the coil is closed, one of the normally open circuits will close as well passing a constant power to the coil keeping it energized.

>Ans. contactor is a heavy duty switch whereas the relay is light duty switch <
>contactor has a hold on contact whereas relay has no such provision <

Sorry Sir, but it's not convincing answer. There are several relay which have 4 contacts, 2NO and 2 NC, example Omron MY4N. If we are using only one NO contact then, we can use the other one as latching/holding contact.

Contactors have non-hinged armatures, typically double-make or double-break device. They are typically in higher load applications and they typically have less contact bounce and more powerful closing forces than standard relays.

By Anonynomous on 9 November, 2010 - 10:05 am

I prefer a more pragmatic definition of Relay vs. Contactor. If, when you energize the device, it goes "click", then it's a relay. If it goes "clunk" then it's a contactor.


means "click" little amount of current to energize the coil

means "clunk" a large amount of current drawn by to start the motor..

relay is mostly integrated in PLC controller for controlling a close loop process..
while MC or TC is typically used for a large motor to start with a large amount of current...

By Wm Seán Glen on 14 January, 2011 - 10:23 pm

Lots of ways of looking at this. Yes, in general, the relay is lighter duty. A light duty relay might be used for current isolation or providing a signal to some kind of monitoring software whilst the contactor would be heavier duty and provide power to a device with more current capability.

The contactor is usually built to be repairable. You can change out the coil for different voltages or flip the contacts to be NO or NC and have at least four sets of contacts (three phases and holding contacts) with the option of adding more to the same armature. If there were an overload added to interrupt current to the coil, it would be referred to as a "motor starter."

Although a Relay is generally non-repairable, you can, however, have different coil voltages and multiple contact options

Are contactors not rated to break faults, whereas relays do not generally have this capability?

By Electrical on 9 March, 2011 - 12:35 am

A relay is use to switch on/off low power devices. A contactor use to switch on/off high power devices.

1 out of 1 members thought this post was helpful...

The differences:

A Relay:

1. Goes Click when energized.
2. Switches loads of lower wattage
3. Applications include control circuitry
4. Generally switch currents less than 10-15 Amperes.
5. Generally switch voltages less than 240 VAC
6. Switch AC or DC
7. Not normally rated in horsepower.
8. Double throw is typical (normally open and normally closed contacts in one unit).
9. Relay coils are AC or DC, but tend to be 5-24VDC with back emf power diodes to protect relay control electronics.
10. The buck just gets passed here. Relays tend to be "pilot" control devices, controlling more powerful contactors.

A Contactor:

1. Goes Clunk when energized.
2. Switches loads of higher wattage
3. Applications include power circuits (from electric motors to a country's main power grids).
4. Generally switch currents above 10-15 Amperes.
5. Generally switch voltages 120 VAC or greater.
6. Switch AC or DC, resistive or inductive loads, but generally switch AC Loads.
7. Usually includes a horsepower rating.
8. Single throw is the norm (either normally open or normally closed contacts, rarely both).
9. 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)
10. The buck stops here. Contactors are the real deal. They can be controlled by smaller, less powerful relays.

By Petar Timotijevic on 22 July, 2011 - 4:21 am

> what is the basic differences between contactor and relay and why can't we use
> the contactor instead of relay and vice versa?

Basic and main difference is that, contactor have special designed chamber vacuumed or filled with special inert gas, which allow HV to switching but not start ARC!!! Relay don't have this, and when use relay on HV with high current arc flux will occur and this situation will be dangerous. Plus relay is smaller contacts are closer and contact platine are smaller may glue together. Relay are often for current to 10A, contactors may go 25A 63A 150A 300A ...

By W.L. Mostia on 22 July, 2011 - 1:37 pm

"Basic and main difference is that, contactor have special designed chamber vacuumed or filled with special inert gas, which allow HV to switching but not start ARC!!! "

I have to disagree with the above statement. While a high voltage contactor may have those features, low voltage (<600V) contactors do not typically have those features. Also, there are high voltage, air-break contactors available. Low voltage contactors commonly have arch extinguishing capabilities via arch chutes (air). The basic difference between a relay and a contactors is that contactors typically handle higher currents and in some cases higher voltages, are of sturdy construction, and have application specific features like high interrupting capacity, high withstand ratings, motor service, cyclic service, heavy-duty service, etc.

William (Bill) L. Mostia, Jr. PE
Sr. Consultant
SIS-TECH Solutions, LP

Any information is provided on Caveat Emptor basis.

from wiki

greater than 15 amps are called contactor
less than 15 amps - Relay...

The 15A limit for a relay is not always appropriate as can be seen on this site concerning a relay which it calls:



The current rating is also not a simple specification because you need to take into account the steady state value as well as the current breaking capability. The graphs for the "Finder" relay in their technical data sheet in the link above cover these considerations very well. I have just installed this relay to control a 3KW hot water cylinder at 220 Volts. It has to switch 13.6 Amperes. I have a timer which turns on this relay. I selected this relay rather than a three phase contactor because it is about a quarter of the price a similar contactor.

By Darryl Dearing on 10 January, 2013 - 3:52 pm

> what is the basic differences between contactor and relay and why can't we use
> the contactor instead of relay and vice versa?

It is my opinion that a contactor is a device that has a 'floating' contact bar that is drawn either away from or towards contacts wheras a relay always has one end of its switch contact mechanism attached to the connection pin/tag. It is nothing to do with current rating as they can be interchanged to a large extent.

By Russ Kinner on 11 January, 2013 - 9:46 pm

The plug-in relay often does and all form "C" contacts have a common contact end - however, most industrial rated "relays" are similar to contactors with a floating contact bar (see the AB 700 series - they have both types listed under "relay").

There are many sub groups under the title relay - safety relays, definite purpose, magnetic or "reed" relays, and of course latching relays. You cna make some generalizations about typical relays but so many styles have been in use over the years that there is always an exception or two.


The distinction of a relay as switching AC (almost always only single phase) or DC pilot/control signals vs a contactor actually switching the full line voltage and current (often three phase) to lights, motors, etc. seems like a highly useful distinction. Contactors often have auxillary contact sets suitable for much lower currents built right into the operating mechanism of the contactor in addition to the main contacts. I don't think I've ever seen that in a relay, just add other relays in parallel/series to perform the equivalent function.