Contactor / relay

[thomo27]

Hi

Please can anyone confirm what the difference is between a Relay and a Contactor. I was told a Contactor is a small relay but not convinced, looking at my course notes It indicates it is a device used to switch motors, there seems to eb some debate on other forums on what the difference is !

Confused

 

[thomo27]

I think im sorted

Ive just read the following explanation

A contactor is a heavy duty relay (so not a small relay) which is used to switch electric motors and lighting loads.

 

[Lectrician]

A relay is typically rated at 10amp or less, designed for resistive loads, not designed for being 'held in' for long periods, can be unplugged from its base, usually has changeover contacts and two or more poles.

A contactor can be rated at any current, has AC1/AC2/AC3 ratings for inductive loads etc, is designed to be held in for sustained periods, is usually fitted directly to a dinrail, has 3 or 4 NO contacts (can have contact blocks added for extra poles, auxiliary NO/NC contacts).

Both can have varying voltage - 12, 24, 110, 230 etc. I have only ever seen contactors that have 400v coiles and 400v contacts - never relays.

 

[bernardgreen]

Being pendantic


A contactor is a switch, often multi-pole which is operated by an electromagnet.

A relay can be as simple as that or can be more complicated.

A relay can have more than one coil (some have four) and perform some logic functions. Computors have been built using only relays.

 

[breezer]

then again.

not all relays plug in, or have more than 1 coil.

very basic burglar alarms have relays that stay energised for hours, if not days (at week ends)

in summary

contactor = overgrown relay

 

[Taylortwocities]

Wikipedia sayeth:

Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices, not other control devices. Relays tend to be of much lower capacity and are usually designed for both Normally Closed and Normally Open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, a contactor normally only has Normally Open contacts fitted.

 

[plugwash]

I don't think being held in for a long time is a problem for most relays. What I do wonder though is if the small relays I see that claim to have a 16A contact rating can really sustain that rating constantly.

 

[Taylortwocities]

Indeed. When used to work on the old Strowger telephone exchanges there were relays in some of the selectors that had been held in the operated position for years.

When wired as a latching circuit they can do just that.

 

[RF Lighting]

Not always strictly true, but generally relays are used for control, contactors are used to switch a load which is too great for the control circuit.

 

[TicklyT]

In the automotive world a relay/contactor is sometimes called a solenoid

 

[breezer]

the solenoid is what the coil of a relay or contactor is / shoud be properly called

 

[bernardgreen]

or armature.

 

[breezer]

dont agree with that one

 

[ricicle]

The solenoid is the coil, the armature is the iron that gets 'pulled' in.

 

[Taylortwocities]

In a solenoid doesn't the operating core get pulled into the coil when energised and usually this movement is linked to another mechanical action. (eg the semaphore indictor flags on old cars).

In a relay the cation is different as the core of the magnet is fixed and the resulting movement causes contacts to open or close and these 'relay' or signal other electrical functions..