Rainwater Tank Float Switch Australia: Pump Control, Mains Changeover & Overflow
How a float switch controls an Australian rainwater tank: 240V pump start/stop, town-water (mains) top-up changeover, overflow and dry-run protection — for installers, pump shops and tank-package OEMs.
Across Australia — from Perth's scheme restrictions to Melbourne's tank rebates and Brisbane's storm-water harvesting — a rainwater tank is only useful if something decides when the pump runs and when it stops. That "something" is a float switch or level controller. It switches the pump, prevents overflow, protects the pump from running dry, and (with a second switch or solenoid) tops the tank up from town water when rain runs out. This guide is written for Australian installers, pump resellers and tank-package builders specifying level control for 240V single-phase systems.
1. What the float switch actually does on a tank
A tank float switch has up to four jobs, and a clean install separates them onto dedicated switches rather than asking one float to do everything:
- Pump control (fill/drain): start the pump when the tank is low, stop it when full — the classic start/stop hysteresis.
- Overflow prevention: a high-level switch that closes an inlet or sounds an alert before the tank spills.
- Dry-run protection: a low-level switch that cuts the pump before it sucks air and cooks the seal.
- Mains (town-water) changeover: a low-level switch that opens a solenoid on the mains supply so the house never runs out, then closes it once rain refills the tank.
2. 240V pump control in Australia: direct vs contactor
Most Aussie tank pumps are single-phase 240V. A float switch can switch a small pump directly only when its contact rating comfortably exceeds the motor inrush — for example 10(8) A at 250 V AC. For anything larger, or for any three-phase bore/transfer pump, the float must act as a signal into a contactor or relay so the float contacts only carry the coil current. All wiring should follow AS/NZS 3000 (the Wiring Rules), with the pump circuit protected by an RCD as required, and the float leads run in conduit away from the pump's power cable to avoid induced start-up. We supply floats; the final wiring and compliance sign-off are the installer's responsibility.
3. Adding town-water (mains) top-up
This is the feature households ask for most. Fit a high-level float (or a separate conductivity/electronic sensor) that triggers a normally-closed solenoid valve on the mains line when the tank level drops to a set point, and closes it once the tank refills. The two supplies must never run together — a simple interlock or a controller with changeover logic prevents the pump and the mains top-up firing at once. Critically, the mains top-up must be connected through a compliant backflow prevention device per local plumbing authority rules; the float only opens and closes the circuit.
4. Float type for the tank shape
- Cable pendant float: cheapest and most adjustable, hung into round above-ground or underground tanks on a tie-off weight. Ideal for pump control and overflow.
- Vertical rod (stem) float: a float on a fixed rod — best for slimline tanks and under-eave installs where a pendant has no swing room.
- Side-mounted float: bolts to the tank wall at a fixed point for narrow spaces; common on pre-packaged pump stations.
For tank water, a PP (polypropylene) body with an oil-resistant PVC or neoprene jacket and an IP68 rating for continuous submersion is the workhorse. If the tank also feeds drinking water, specify float bodies and cable sheath rated for potable contact — in Australia that means materials compatible with AS/NZS 4020 for contact with potable water.
5. Cable length vs tank height
Order the cable long enough to reach from the mounting point to the controller with slack for the trip angle and future adjustment. A longer cable lowers the effective trip point, so standard lengths (2, 3, 5, 10, 20 m) are easier to manage than cutting to an odd length. For a slimline tank, a rod float removes the cable-length guesswork entirely.
6. Spec checklist for your RFQ
- Tank type and shape (slimline, round, underground) and internal height.
- Pump voltage and current, single- or three-phase, inrush estimate.
- Jobs required: pump control, overflow, dry-run, mains changeover — and how many separate floats.
- Mounting: pendant, rod, or side-mount.
- Body material and potable rating (AS/NZS 4020) if the water is drinking water.
- IP rating (IP68 for submerged) and cable length.
ELEHPD supplies cable and rod float switches in PP bodies with IP68 sealing, NO/NC contacts and leads sized for direct pump control or contactor signalling, built to IEC practice and suitable for Australian 240V tank and bore systems when wired by a licensed installer.
FAQ
Can a float switch run a 240V rainwater tank pump directly in Australia?
Only for a small single-phase pump whose inrush stays within the float's contact rating (for example 10(8) A at 250 V AC). For most tank pumps, the float should signal a contactor so the contacts only carry the coil current and the pump motor is switched by the contactor, in line with AS/NZS 3000 wiring practice.
How do I add town-water (mains) top-up to a rainwater tank?
Fit a high-level float (or a separate level sensor) that opens a solenoid valve on the mains supply when the tank drops below a set level, and closes it once the tank refills. The float and solenoid are the two control points; the pump and the mains top-up must never run together. Always fit the mains feed through a backflow prevention device as required by local plumbing rules.
Which float switch suits a slimline or under-eave tank?
In a narrow slimline tank use a vertical rod (stem) float or a side-mounted float bolted to the wall, because a pendant cable float needs vertical swing room it may not have. For round above-ground or underground tanks a cable pendant float on an adjustable tie-off is the cheapest and most flexible option.
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Supplying the Australian market
ELEHPD manufactures and wholesales float switches and level controllers to distributors, pump packagers and OEMs. For the Australian market we supply factory-direct with English datasheets and labelling, OEM/private-label options, and short lead times — spares and documentation are supplied from the factory, not from a local warehouse. See our Australia market page for voltage, standard and application notes.
Talk to us about your specification
Send the tank type, pump rating and the control jobs you need and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding and buyer-specific cartons are available on qualified volumes.