Measurement and Control Equipment

Cable Float Switch: Working Principle and Pump Control

Learn how cable float level switches work, how to wire them for filling or emptying, how to set the working band and where they are used.

ORFA Technical TeamUpdated: Oct 30, 20263 min read

In many systems, such as water tanks, septic and wastewater pits, submersible pump applications and booster set tanks, starting and stopping the pump at the right time depends on reliable level detection. A cable float switch is a simple, durable level control device: a float rests on the liquid surface, and as the level changes its tilt angle changes, operating a switch inside that opens or closes the electrical circuit.

This article covers the working principle of cable float switches, fill and empty wiring, installation, benefits and applications.

What Is a Cable Float Switch?

A cable float switch consists of a sealed plastic float containing a microswitch and a moving element that actuates it (usually a ball), attached to a flexible electrical cable. The cable is held in the tank by a weight or fixing point, and the float swings up and down with the liquid level.

How Does It Work?

At low level the float hangs down under the weight of the cable.
As the liquid rises, the float floats and pivots upward around the fixing point.
When the float passes a certain tilt angle, the internal element shifts and the microswitch changes state.
When the level falls again, the float tips down and the contact returns to its original state.

The difference between the switch-on and switch-off levels (the working band) is set by the free cable length between the fixing point and the float. The longer the free cable, the wider the band and the less frequently the pump starts.

Fill and Empty Wiring

Models with a changeover (NO/NC) contact can work in two ways depending on which cable cores are used:

Application	Operation	Example
Emptying	Pump starts when the level rises and stops when it falls.	Wastewater pit, drainage sump, septic tank
Filling	Pump starts when the level falls and stops when it rises.	Water tank, roof tank, booster set feed tank

Benefits

Versatility: The cable length allows use in tanks, reservoirs and wells of different depths.
Reliability: The simple mechanical design has a low risk of sticking in dirty or particle-laden water.
Durability: Available with body and cable materials suited to different liquids and temperatures.
Fill and empty: Changeover models can be used for both applications.
Easy installation: Simply hung from the tank top or fixed to the pump riser.
Economical: A low-cost, maintenance-free method of pump automation.

Tip: Choose a position where the float can swing freely without catching on the tank wall, pump cables or pipes. If the switch will control a pump directly, compare its contact rating with the motor current; if necessary, connect via a contactor or pump control panel.

Applications

Industrial plants: Level control in wastewater plants, process and collection tanks
Pump systems: Submersible and drainage pump automation
Booster sets and water tanks: Tank filling and dry-run protection
Residential: Water tanks, rainwater tanks and septic tanks
Other: Pool balance tanks, fish ponds, wells and groundwater drainage

Frequently Asked Questions

How is the working band of a cable float switch adjusted?

By changing the free cable length between the fixing point or weight and the float. The longer the free cable, the larger the difference between the on and off levels.

Can the same switch be used for filling and emptying?

Yes. On models with a changeover (three-core) contact, the switch can be wired for filling or emptying by selecting the appropriate cores.

Can it be used in wastewater?

Yes. Cable float switches are among the most widely used level switches for controlling submersible pumps in wastewater and drainage pits, provided the cable and body materials suit the liquid.

Conclusion

Cable float switches are a simple, reliable and economical solution for pump and tank automation. With correct wiring, the right cable length and a mounting point where the float can move freely, they work trouble-free for a long time. Explore other level solutions on our Level Control Devices page.

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