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Wiring for Dual Float Switch System; Well (high level ON), cistern (low level ON)

A common use of float switches is in potable water systems, specifically in systems where a well pumps water into a cistern. What if you want the pump to run only when the water is high enough in the well, and when there is enough volume in the cistern to store water? What if you can only find float switches that are rated under the nameplate HP of your pump? Wiring a potable water pump in a 2 float switch setup is no longer an issue with the utilization of a electro-mechanical relay in addition to two Sump Alarm 3-wire float switches. The purpose of this article is to help you wire this dual float switch and electromechanical relay into your system.


Sump Alarm 2359 and 2368 series 3-wire float switches are rated for direct control of pumps up to 1/2 HP or 13 Amps at 120 or 240 VAC for non continuous operation of the pump. For most of us, this won't suffice, since most well pumps are 1 HP or larger. The diagram below details the use of either a 2359 or 2368 series float switch, two in series, wired for opposite operation in conjunction with a relay. The float switches provide "logic" to open and close the relay, where the relay is handling the higher current required to run the pump. 

The well float switch in this diagram is wired in EMPTYING operation which omits the blue wire and uses the brown wire, this makes sense because our well is filled by groundwater, and our well pump must empty the volume of water once the water in the well is high enough. 

The cistern float switch in this diagram is wired in FILLING operation which omits the brown wire and uses the blue wire. This makes sense because we want the well pump to fill the cistern to the fullest point, but not overfill.

In this configuration, the pump will only run when there is volume available in the cistern and the well has enough water. This circuit provides dry run protection for the pump as well as overflow protection for the cistern so that the pump is protected and water is not wasted. 


The wiring diagram for this system assumes the use of a single phase pump, 2 phase pumps can be utilized in this system however, the pump will require the second phase be run separate of the "logic circuit" in the above diagram. Contact us for a clarification if you are unsure.

This Packard electro-mechanical relay is available here, at the time of this article the price was $8.34:


All connections made in this diagram are to be completed according to NEC standards. 


If you have further questions, please contact us!

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