What is the necessity of a starter? Can a single pole-switch replace it?

Most smaller, single phase motors usually have a permanent magnet armature that is pushed / pulled around by the rotating inductive field produced by the stator (outside) windings. The inductive field rotates simply as a result of the positive / negative alternations of the 60HZ AC current flowing through the windings. The problem is that when the voltage is applied, the 60HZ is applied immediately, the rotation of the field through the windings begins immediately, and the armature has no chance to react (or catch up, as it were) to the field.

The start cap provides that electrical "push" to get the motor rotation started. It does this by creating a current to voltage lag in the seperate start windings of the motor. Since this current builds up slower, the armature has time to react to the rotating field as it builds up, and to begin rotating with the field. Once the motor is very close to it's rated speed, a centrifugal switch disconnects the start cap and start windings from the circuit. Watching a single phase motor starting you can see that this all happens very quickly.

Without a start cap (such as when one burns up) when the voltage is applied, the motor will just sit and hum. But if you were to grab the shaft and give it a spin, the motor would (usually) start and run normally.

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Hi,

A motor starter usually has an overload heater incorporated into it. A single pole switch does not have that type of protection. There are many brands of fractional motor starter switches. These types of switches are sized by the motors full load amperage. These types are dual purpose being that they can be used as the motors isolation switch and also they can be used as motor protection for the connected motor.

thanks

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