Answer / jesus

Relays and Contactors are electromagnetic switches. The only
difference is that relays are usually used for low voltage
applications while contactors are used for higher voltage
application. Contactors usually have Overload protection.

Some examples that I can give (at least in Manufacturing of
Industrial Control panels):

-Relays are use as electromagnetic switches to control
certain parts of a circuit (low voltage application). A
better example would be such as if you want your circuit to
sound a horn when a certain abnormality is happening at a
certain period of time, then depending how you set up your
circuit, a specific relay will either open or close and you
horn will start making the sound.

-Contactors can be used for example, to start motors or a
number of motors that require a higher voltage in order for
the motor or motors start working. In the example that I
just gave, contactors work as starters.

Answer / sandeep

Contactor is a switching device. Unless & until you give
command it wont operate. Contactor is not a sensing device.
on the other hand Relay is the device which sense the
ubnormality & give command accordingly. Relay differentiate
normal & ubnormal condition which contactor can not.

In short if only contactor is connected in circuit.. in
case of ubnormal like OV or OC it will burn.. but if it is
connectedin coordination with relay.. relay will sense the
fault & give signal or command to contactor to trip

Answer / vikrant patel

First Clear Relay Means
1. Protective relay
2. Control Relay.

If talking about Protective relay (Example: over current
Relay, Electronic motor protection relay..etc)
so protective relay is for Protection of circuit
and functionally different from contactor.
they have only potential free contact at output which can
be used in control circuit.

if talking about control relay
1. Power relay (which have Change over contact with high
current capacity)
2. Solid state relay
3. Simple control relay. (Which have Change over contact
with low current capacity call SPDT)

This all relay has functionally similarity with contactor
that they are electromagnetic device (except SSR) but
difference
- relay have changeover contact (NO, NC& Common) while
contactor have power contact NO) & auxiliary contact (NO or
NC).

Main difference is

- Contactor is used to Control power Circuit while relay
are used for control circuit (except Power relay which is
now a days introduce for DC/High voltage application).

Answer / akshay pramod

1) A contactor is an electro-magnetic switching device (a
relay) used for remotely switching a power or control
circuit.[1] A contactor is activated by a control input
which can be a lower or higher voltage / current than that
which the contactor is switching. Contactors come in many
forms with varying capacities and features. Unlike a
circuit breaker a contactor is not intended to interrupt a
short circuit current.

Contactors range from having a breaking current of several
amps and 110 volts to thousands of amps and many kilovolts.
The physical size of contactors ranges from a device small
enough to pick up with one hand, to large devices
approximately a metre (yard) on a side.

Contactors are used to control electric motors, lighting,
heating, capacitor banks, and other electrical loads.

2) A relay is an electrical switch that opens and closes
under the control of another electrical circuit. In the
original form, the switch is operated by an electromagnet
to open or close one or many sets of contacts. It was
invented by Joseph Henry in 1835. Because a relay is able
to control an output circuit of higher power than the input
circuit, it can be considered to be, in a broad sense, a
form of an electrical amplifier...

Answer / velmurugan

01. contactor and relay working fuction same but
02. we are called relay we are using control circuit
03. We are called contactor we are using power circuit

Answer / don

Answer #5 is the best one so far.

I think the question relates only to relays as switching
devices, not protective relays.

A "relay" is a solenoid operated switching device, having
one or more sets of change-over contacts, commonly used to
control (switch) other devices.
The contacts only "break" at one point.

A "contactor" is also a soleniod operated switching device,
but the contacts are discrete NO (normally open) or NC
(normally closed) contacts - not change-over. Contactors
are usually used to switch higher current power circuits
(as opposed to control circuits), such as motors and
lighting.
Contactors usually have three main poles which are fully
rated for its' AC3 rated current, and often a fourth
auxillary contact which is only rated at 10A AC1 - suitable
for control circuits only.
The contacts have a double-break - two points of break.

Answer / maddy

contactor only makes or break accordingly as it is commanded
throw relay....while relay is just like a sensor.
Contactor mostly uses for motor protections in industrial
area for high load applications.
Relay is a low power consumption device.

Answer / shaheed

Relay is an Electromagnetic Switch.It can either make a
circuit or break the circuit with a preset value given by
the manufacturer or according to the functional operation.

But where as Contactor is a device which normally preferred
in Motor Protection circuit.It can either make or Break the
circuit with the rated Power.but not in line with the
Abnormality or any set value

Answer / pankaj

Relay: 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.

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

Answer / wleob

1) All of the previous answers are mostly correct.

2) In general, a relay and a contactor have at least the
same two basic parts:

a. A coil that makes the contacts close or open. The coil,
whether energized by AC or DC always uses much less current
(amps) to operate than the current, AC or DC that the
contacts can carry. Coil ratings can be from 12 VDC to 600
VAC, for example.

b. Contacts, rated DC or AC that open or close a circuit to
a load (resistance or inductance) which demands more current
(amps) than the coil does. Relay contacts are usually
applied to lower amperage circuits and Contactor / Motor
Starter contacts usually carry higher voltages and amperage.

3) AC and DC coils are built differently. AC coils have
steel plates to break up the eddy currents inherent in AC.
As AC goes "through zero" 60 times per second, no
discharging diode is required. The rating on the coil will
state whether it is for 60 Hertz (cycles per second) , 50
Hertz (CPS) or 60/50 Hertz, meaning it can be used in the
USA or Canada. DC coils usually have a diode and/or a
capacitor for the inherent discharge of the coil when the
voltage is removed. The current going through the coil must
be discharged as the field in the DC coil collapses.

4) AC contacts in low power applications don't require any
special arc chutes as AC, again goes through zero 60 times
per second (50 times per second in Canada). DC contacts in
low power applications do not require arc chutes. However,
as the current being carried gets larger and if the load is
not pure resistance, the discharge power must be dissipated
or "blown out" in an arc chute.

5) In summary, relays are usually applied to control
circuits and in lower power applications while contactors
usually imply that they are controlling larger loads with
higher current (amp) requirements. Industrial relays
typically can carry 5, 10 or 20 amps as do the relays in
your cars fuse box for your headlights, blower motor, or
your trailers electric brakes. However, though called a
starter "relay" it is contactor that will carry at least 100
amps to run your starter motor. AC Motor "starters"
/contactors typically have 120 VAC coils or 460 VAC coils
and can run motors that require from 5 amps to 100s of amps.

Hope this helped,
WLeoB
BSEE '71
Canton, MI

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