why do we need to use contactor in electrical circuits?

Question

i need to know that what is the function of contactor in electrical circuits i do have some idea but i am little confused because i can use relay instead of using contactor both can switch to close and open when energised and de energised so why would we use contactor does it gives you more current at the output or is there any other reason.can anyone please explain.thanks

Answer 1

The use of a contactor is based strictly on the application. There are different types of contactors from "General Purpose" to types that are specifically designed for the intended application. The PRIMARY difference between a contactor and relay is the ability of the contactor to "make" and "break" the circuit under high current conditions. The contacts in a contactor are designed to handle the in-rush current of the "make" or energized function and the arcing between the contacts associated with the "break" function (de-energized). As far as application is concerned... you need to be more specific in what you are trying to accomplish. As there are as many different types of relays as there are contactors. Using the wrong type in any application can create a lot of problems that using the correct one could avoid. In some applications contactors are a requirement rather than a solution, which is not necessarily true with a relay. The rule of thumb is "You can almost always replace a relay with a contactor and retain the same function, but only in special cases is the reverse true". As far as current limiting is concerned, when this function is added to a relay then it becomes a "Motor Control". The current limiting is to protect the motor it controls and provide contact closures that control ancillary equipment that maybe associated with the motors operation in a system environment such as a manufacturing or production line.

Answer 2

Electrical Contactor

Answer 3

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RE:
why do we need to use contactor in electrical circuits?
i need to know that what is the function of contactor in electrical circuits i do have some idea but i am little confused because i can use relay instead of using contactor both can switch to close and open when energised and de energised so why would we use contactor does it gives you more current...

Answer 4

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The counter EMF is created by the collapsing magnetic field of the coil in the solenoid. So yes, there will be a counter EMF in your circuit. In the DC side of the circuit it is most often controlled one of three ways. Putting a Resistive-Capacitive) RC network, a clamping diode, or a varistor across the load. It is best to place the protective circuit close to the load (solenoid). The clamping diode forward circuit rating must be equal to or greater than the load current. Diode PIV rating must be three or four times greater than the supply voltage at 24 VDC The unpolarized (AC) snubber capacitor should have a rating two or three times greater than the supply voltage. The capacitor value may be: 0.5 mF for a load inductance of 25-70mH, or 25 mF for a load inductance of 70-180 mH. Snubber resistors may be 1-3 ohm, 2W. Resistor values should be increased up to 47 ohm, .5W for R-load exceeding 100ohm. Added: The function of a capacitor across the output of the power supply will flatten out any ripple in the output of the DC power supply. It will do little for any counter EMF from the solenoid because the time constant for the charging of that big of capacitor would be to long to be much use.

Answer 5

A contactor and a relay are pretty much the same thing except that a contactor usually includes a current limiting section in it for safety purpose. It's not a circuit breaker, but it can keep a fire from starting.

Answer 6

Yeah. What Eugene said. Plus a 'contactor' usually implies a high-power device (something switching on the order of a few hundred Watts or more) whereas a 'relay' usually implies a device that switches a few tens of Watts.

It's a kind of a grey area ☺


Doug

Answer 7

protection of system bec protection of motor through the contactor .contactor is a swtiching device
and Contactors perform the same task of switching a electrical circuit

Answer 8

What Is A Contactor

Answer 9

Since MCB is a safety device it should be used first.

Answer 10

in detail
http://www.allaboutcircuits.com/vol_4/chpt_5/2.html