Float switch

What is a float switch?

A float switch is a level switch whose position changes with the liquid level in a tank, opening and closing its contact accordingly. On cable types, the float at the end of the cable tilts up as the water rises and hangs down as it falls, and the contact inside changes over.

Where is a float switch used?

It is used in water tanks, booster systems, irrigation ponds, drainage and septic pits and wells to run pumps automatically and prevent dry running. It is the simplest and cheapest way to sense level in pump control.

Types and selection

There are cable (hanging) float switches, rod float switches and mechanical float switches. Cable float switches usually have a changeover contact: one contact is used to fill a tank, the other to empty it. The cable length and the position of the counterweight set the working level range. For drinking water, choose a float switch made of certified material.

What to watch out for

The float switch contact is used to supply the contactor coil, not the motor directly. The float must move freely in the tank and not catch on the pump inlet or pipes. In wastewater pits floats get dirty over time and should be checked regularly.

Terminals

Float switch (cable)

Black (BK): common (C)
Blue (BU): normally open (NO)
Brown (BN): normally closed (NC)

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