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.
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
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
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
- relay have changeover contact (NO, NC& Common) while
contactor have power contact NO) & auxiliary contact (NO or
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).
1) A contactor is an electro-magnetic switching device (a
relay) used for remotely switching a power or control
circuit. 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...
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
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.
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
Relay is an electromagnetic device. There are two types of
relays __ Power relay (or contactor) and Control relay( or
The function of a contactor is to use a relatively small
amount of electrical power to control the switching of a
large amount of power
Control relays are frequently used in the control of low
power circuits or other relays
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.
For an 100kw generator, only 50kw of load is connected. Will
the generator generate only 50kw or 100kw. If it generate
100kw what happens to rest of the 50kw. What happens if we
connect more than 100kw of load?
I have a 3 phase 600 volt prim. feed and a 120/208 sec.
Isolateing tranformer .We are using this system for safety
against shock . What is the proper grounding ?? Does the
common on sec. get earth ground ???
i want to know how to calculate the battery capacity based
on the UPS . ex i want to run have one kva UPS Which should
run 10 hours ? in that case how many batteries to be
installed and what will be the AH Value .