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Using a Float Switch To Start and Stop 220Volt Pump
How to start and stop a 220 Volt Pump with a float switch is a common question.
The correct way to start and stop a 220 Volt pump is to turn both legs on, and both legs off simultaneously. To do this, we introduce a contactor. The contactor not only starts and stops both legs, but also reduces the amount of current flowing through the float switch from 10 amps or so down to about 1/4 amp. It doesn't matter who's float switch is being used, this will extend the life of the float.
Here in the US, 220 Volts is created by having (2) 110 Volt "Hot Legs". To keep things simple, we make 220 Volts by taking the difference between +110 and -110 Volts. 
Below is a "how to diagram" for the connection of the contactor. The float switch will control the contactor, and the contactor will control the pump. While Sump Alarm only sells the float switches, feel free to write into us and we will be glad to send you some links to amazon where you can purchase the remaining parts.
Someone might say "You could get a 220 Volt Float switch". It's true, they're out there. We don't believe in them. When you see the operation of the contactor, it will be clear that (2) microswitches housed underwater just wouldn't be adequate replacement.

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