Generally speaking, the selection of contactor has many factors, it is closely related to the load, and there are many kinds of loads, and different loads have different current characteristics. We must understand the different starting currents of different loads.

1. heating element load 1.4 times (AC-1)

2. lighting load 15 times (AC-5b)

3. low voltage transformer load 15-20 times (AC-6a)

4. capacitor load up to 20-30 times, usually in the circuit string additional inductance or resistance current limit (AC-6b)

5. times the motor load 3-5 winding motor switch. (AC-2); squirrel cage motor starting current is 6-8 times the rated voltage, the normal operation after the current interruption is rated current, but because of the back EMF voltage is only 0.17 times the rated voltage (AC-3), which belongs to the class AC-4 in the start switch on and off, should be carried out at 6 times the current, so the use of the most harsh conditions. The selection of contactors should meet the requirements of the control device, in addition to the rated voltage rated voltage should be charged with the same equipment, controlled equipment load power, use category, operation frequency, service life, installation mode and size and economy is the basis for the choice of