What is a Contactor ? How does it work ? And how to choose a correct contactor replacement ?

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What is a contactor ? -
A contactor is one of the main electrical circuit parts, which can stand on it's own As a power control device - or as a part of a starter -
Contactors are used to make and break power supply lines running to a load -.
Or, To repeatedly establish and interrupt an electrical power circuit. -
Contactors are used starting with light loads - To the most complex machine control -.
Contactors are mainly used with Motors, Transformers, Lighting, Heaters, And distribution panels -.
And it can be considered as the intersection point, - Between control - and power circuit, - because it's controlled by the control circuit, - And it's controlling the connection between power and loads -.
So you can find the contactor symbol in both, - Control and - power drawings -.
Contactor is used when frequent start / stop - Or remote controlling is required -.
The contactor is consist of -
2 Iron cores - one is fixed - and the other one is movable -
The coil - and it's an insulated copper coil - located on the fixed iron core -.
6 Main contacts - for power connection - 3 are fixed - And the other 3 are free to move - with the movable iron core -.
These contacts are made from pure copper -. And the contact points are made from special alloy - to with stand with the high starting current - and temperature.
Spring - It is located between coil - and the movable core -.
Auxiliary contacts -
It could be normally open - or close - And it is not designed to carry high load same as the main contacts - It allows us - to make on and off for some light current loads - such as - contactor's coil - relays - timers and many other control circuit parts.
- And it is linked to the contactor mechanism - so when the contactor is energized - it will change it's status from normally open to close - and vice versa -.
How a contactor works - ?
When applying the control voltage on the coil leads - A 1 and A 2 -. A magnetic field will be generated - attracting the movable iron core towards the fixed core - So the movable contacts which are fixed to the movable core - will move as well towards the fixed contacts - to make a contact and allow the power lines to run to the load -.
If we interrupt the control voltage supplying the coil - the magnetic field will disappear - and the force spring - will push the movable parts to back again to it's original position - that will lead to interrupt the power going to the load
How to choose the correct replacement for a contactor ? -
- First - you have to check the coil voltage - it is the control voltage which is used - to energize the contactor - And you can find it printed - on the contactor - Between A 1 - And A 2 - It must be same as the used contactor -
- Second - check the auxiliary contacts - if available - How many normally open and close - were used in the old contactor.
- Third - check the contactor rating - It is the contactor designed capacity - And it is printed in a table on the contactor - If we checked this contactor table - It is written - from 18.5 - to 56 kilo watt - Which one is the contactor rated ? - It depends on - your load - If your load is a motor - so you have to check - The A C 3 table - Then - Say your power network voltage is - 400 Volt - that means that - this contactor rating is 30 Kilo watt

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