A tethered float switch is a sealed float on a cable. Tied off at a fixed point in the pit or tank, it hangs down when the water is low and tips up as the water rises. Inside, a switch changes state at a set angle. It's simple, cheap and very reliable, which is why it's still the most common way to switch pumps and alarms on water level.
The live float switches in the Float Switches & Level Sensors range are the Maxijet 9006 and the Hyjet HFS.
The two switches
| Maxijet 9006 | Hyjet HFS | |
|---|---|---|
| Rating | 240V AC, 6A | 240V AC, 10A |
| Switching angle | 25° from horizontal | 20° from horizontal |
| Contacts | Microswitch, NO and NC | Wired NO or NC |
| Cable | Neoprene 6mm, 3 x 0.75mm² | Neoprene H07RN-F 10mm, 3 x 1.0mm² |
| Other | ABS housing, 0–60°C liquid, IP68 at 20m | Sliding detent action to avoid wave-induced switching; 10 million switch contact life |
| Cable lengths | 10, 15, 20, 30, 40, 50m | 10, 20, 40m |
| Price | $111.05 (10m) to $452.05 (50m) | $94.55 (10m) to $210.05 (40m) |
The Hyjet HFS's sliding detent action is worth noting for turbulent pits: it stops the switch chattering on and off as waves slap the float.
Tether length sets the pumping range
The length of free cable between the tie-off point and the float decides how far the water rises and falls between switching on and off. A longer tether gives a bigger range, so the pump runs less often for longer. A shorter tether gives a tighter range and more frequent starts. Set it so the pump stops with the pump still covered (most submersible pumps shouldn't run dry), starts with enough working volume to avoid short-cycling, and the float can swing freely without catching on the pit wall, pipework or the pump.
NO or NC: emptying or filling
- Emptying (pump-down): the switch closes when the float rises, so the pump starts as the pit fills and stops as it empties. This is the normal set-up for sumps and pump stations, and for a high level alarm.
- Filling (pump-up): the switch closes when the float drops, so a pump fills a tank as the level falls and stops when it's full. Also used for low level alarms.
Both switches can be wired either way. The 9006 has a microswitch with both normally open (NO) and normally closed (NC) contacts; the HFS is wired NO or NC for fill or empty duty.
The current rating decides how it's wired
The 9006 is rated 6A and the HFS 10A at 240V. A float can switch a small single phase pump directly only if the pump's current, including its starting current, sits comfortably within that rating. For larger pumps, three phase pumps or more than one pump, the float should switch a pump control panel, which switches the motor. Floats on an alarm circuit, like the Maxijet level alarms, typically run on a low voltage float circuit.
How many floats
A simple sump uses one float. A dual pump sewage station typically uses several: pumps off, duty pump on, standby pump on and high level alarm, each at its own height. Space them so they can't tangle.
Hydrostatic level transducers and conductivity probes are also listed in this collection but aren't orderable online at the moment; contact PSA if a job needs continuous level measurement. All wiring to 240V must be done by a licensed electrician.
Frequently Asked Questions
How do I set the on and off levels of a float switch?
By the length of free cable between the tie-off point and the float. A longer tether gives a bigger difference between on and off; a shorter tether gives a tighter range.
Can a float switch run a pump directly?
Only if the pump's current, including its starting current, is well within the float's rating: 6A for the Maxijet 9006 and 10A for the Hyjet HFS. Larger pumps need a controller.
What's the difference between NO and NC on a float switch?
Normally open closes when the float rises, for emptying a pit or a high level alarm. Normally closed closes when the float drops, for filling a tank or a low level alarm.
Why does my float switch chatter on and off?
Waves or turbulence can rock the float around its switching point. A float with a detent action, like the Hyjet HFS, resists this.