how AC Contactors Work, Select and Connect

- Aug 02, 2019-

The main job of ac contactors is to turn on and disconnect the electrical circuits of the electrical appliances. Two contacts are used to reduce the damage caused by arcing instantaneous breaks and extend the life of the main contact. Auxiliary contact replacement is easier and cheaper. (The time difference and small movement of the main auxiliary contact saline respectively, so it will not affect the use of electrical work.)

Such as: when the suction, the auxiliary contact first absorbs through a small current, the main contact when the suction will not produce a larger arc. When disconnected, the main contact is disconnected first, and then the auxiliary contact has a current flowing through, and there will be no larger arc when the main auxiliary head is disconnected.

1, AC contactor working principle:

When the coil is energized, the static iron core produces electromagnetic suction force, will move the core to absorb, because the contact system is linked with the moving iron core, so the moving iron core drives three moving pieces to run at the same time, the contact closed, thus connected to the power supply. When the coil is off, the suction force disappears, and the dynamic iron core linkage part is separated by the spring's reaction force, causing the main contact to disconnect and cut off the power supply.

2, AC contactor selection:

(1) Continuously running equipment.

The contactoris is calculated at 67-75%, i.e. 100A AC contactor, and can only control equipment with a maximum rated current of 67-75A or less.  

(2) Intermittent operation of the equipment.

The contactor is calculated at 80%. That is, the AC contactor of 100A can only control equipment with a maximum rated current of 80A or less.

(3) Repeated equipment for short-term work. Contactors are based on 116-120%. That is, 100A AC contactor, can only control the maximum rated current is 116-120A or less equipment.

3, AC contactor access:

One: General three-phase contactors have a total of 8 points, three inputs, three outputs, and two control points. The output and input are corresponding and are easy to see. If you are to add a self-locking, you also need to connect the line from one terminal at the output point to the control point.

Two: First of all, you should know the principle of AC contactors. He uses external power to add to the coil, creating electromagnetic fields. Power-up absorbs and the contact point disconnects after power is off. Once you know the principle, you should figure out the contact points of the additional power supply, that is, the two contacts of the coil, usually in the lower part of the contactor, and on one side. Several other inputs and outputs are generally in the upper part, as you know at a glance. Also note the voltage of the additional supply (220V or 380V), which is generally marked. And note whether the contact point is normally closed or open. If there is self-locking control, according to the principle of the line on it.