How to choose a float switch or water level controller: contact type, voltage and current rating, cable length, material, IP rating, and how to specify for clean or dirty water, tanks and pumps.
A float switch is the cheapest, most robust way to detect a liquid level and switch a pump, valve or alarm without electronics in the wet end. For panel builders, OEMs, water-treatment packagers and importers buying from Asia, the part number is decided by the medium, the voltage the contacts must break, and how the float is mounted. This guide covers the parameters that actually change the model, so the switch you specify survives the liquid it sits in.
Inside the sealed float is a tilt- or position-sensitive mechanism (a mercury-free rolling ball or a reed switch) that opens or closes a contact when the liquid lifts the float past its trip angle. There is no controller to program and almost nothing to fail, which is why floats still outlast far more expensive sensors in sumps, tanks and boreholes. The two jobs are level detection (tell me when the tank is full or empty) and direct load switching (turn the pump or solenoid on or off).
The contacts must break the actual load, not just signal a PLC. Check both numbers on the datasheet:
| Parameter | What to specify |
|---|---|
| Contact rating | e.g. 10(8) A at 250 V AC / 24 V DC — must exceed the pump or valve inrush |
| Contact form | NO (normally open) for "fill", NC (normally closed) for "drain" |
| Signal vs power | low-current versions only for PLC input; power versions switch the load directly |
A switch sized only for a 24 V signal will weld its contacts the first time it tries to break a 1.5 kW pump. Always match the rating to the load it switches, with margin for motor inrush.
The body spends its life submerged. Match it to the liquid:
Also confirm the specific gravity the float is calibrated for — a float tuned for water will not trip in a light oil, and one tuned for heavy slurry may never sink in clean water.
Specify the cable length to reach from the mounting point to the controller with slack for the trip angle, and choose the sheath: neoprene or PVC for water, oil-resistant for pits. The ingress rating should be at least IP68 for continuous submersion, and the temperature range must cover both the liquid and any steam or frost above it.
A float used to stop overflow (turn the pump off when full) needs a normally-closed contact that opens at high level; one that empties a pit (pump on when empty) needs normally-open. Two floats give hysteresis — a high switch to start the pump and a low switch to stop it — so the pump does not short-cycle. Get the logic backwards and the pit overflows or the pump runs dry.
ELEHPD supplies cable and rod float switches in PP, POM and stainless bodies with IP68 ratings, NO/NC contacts and leads sized for direct pump control, built to IEC practice and ready to drop into sumps, cisterns, boreholes and OEM water systems.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.