Float Switch Symbol
Definition: The Float Switch symbol represents a level-sensing switch whose contacts open or close based on liquid surface height, standardised under IEC 60617 as a mechanically-actuated switch with a float actuator, used in circuit diagrams to denote automatic liquid-level control.
Also known as: liquid level switch, ball float switch, level switch, float valve switch, buoyancy switch.
What the Float Switch symbol means
The Float Switch symbol denotes an automatic switching device that responds to the rise or fall of a liquid surface. When the float rises with the liquid level, it actuates the switch mechanism, either opening or closing the circuit path between the In (in) and Out (out) terminals.
Float switches are fundamental to pump control and tank management systems. They prevent tanks from overflowing by cutting power to fill valves, and prevent pumps from running dry by de-energising them when liquid drops below a safe level.
How to identify the Float Switch symbol
The float switch symbol is drawn as a standard switch contact (a gap with a diagonal actuating bar) combined with a circle or oval representing the buoyant float. In schematic representations it resembles a single-pole switch with a curved or circular operator symbol attached, indicating mechanical actuation by buoyancy. The two terminals, In (in) and Out (out), represent the switched circuit connections.
Function in a circuit
In a circuit, the float switch acts as an automatic single-pole switch that completes or breaks a control circuit depending on liquid level. As liquid rises and lifts the float, the internal lever mechanism actuates the switch contacts; as liquid falls, the float drops and the contacts return to their resting state. This allows the switch to directly control pump motors, solenoid valves, alarms, or relay coils without requiring manual intervention.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 defines the float switch as a mechanically-actuated switch (function qualifier: float/buoy actuator); the symbol combines the basic switch contact graphic with a float operator circle per IEC 60617-07. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 represents the float-operated switch using a standard switch contact with an annotated actuator label or circle indicating float operation. |
| Key difference | Both standards use a similar contact-plus-actuator representation; IEC uses a standardised operator qualifier shape while ANSI uses a labelled actuator annotation, but the functional intent is identical. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Contact ratings typically 5 A to 15 A at 120 V AC or 250 V AC; DC ratings 1 A to 10 A at 12–48 V DC; operating temperature -20 °C to +85 °C for most types; cable lengths 1 m to 10 m standard.
Where the Float Switch symbol is used
- Sump pump control: float switch de-energises the pump motor when the pit empties to prevent dry running
- Water tank level control: float switch cuts power to the fill solenoid valve when the tank reaches maximum capacity
- Sewage lift stations: float switches at high and low levels start and stop submersible pumps automatically
- Aquarium and fish-pond top-up systems: float switch activates a solenoid to replenish evaporated water
- Industrial coolant tanks: float switch triggers an alarm or pump when coolant level falls below minimum
- Agricultural irrigation reservoirs: multiple float switches provide multi-stage level monitoring and pump sequencing
Example
In a residential sump pump circuit, the float switch (In terminal connected to the 120 V AC hot line, Out terminal to the pump motor) sits in the sump pit. When groundwater raises the float to the trigger point, the switch closes and starts the pump; once the water level drops below the lower setpoint, the float falls and opens the circuit, stopping the pump.
Key facts
- The Float Switch symbol represents a buoyancy-actuated single-pole switch that opens or closes based on liquid surface height, per IEC 60617-07.
- The two terminals are In (in) and Out (out), representing the line-side and load-side connections of the switched circuit.
- Float switches are available in normally-open (NO) configuration, where the circuit closes as liquid rises, and normally-closed (NC) configuration, where the circuit opens as liquid rises.
- Typical contact ratings range from 5 A to 15 A at 120 V AC, with DC variants rated at 1 A to 10 A at 12–48 V DC.
- Float switches are used in sump pumps, water tanks, sewage lift stations, industrial coolant systems, and aquaculture installations.
- The float actuator is the distinguishing symbol element: a circle or oval attached to the switch contact line, indicating mechanical actuation by buoyancy rather than by hand or temperature.
- In wiring diagrams, the float switch designator is typically S or LS (level switch), followed by a number (e.g., LS1).
Diagrams that use this symbol
- water pump connection diagram
- water pump wiring diagram
- fuel pump wiring diagram
- 3 wire float switch wiring diagram
- submersible pump wiring diagram
- well pump wiring diagram
- bilge pump wiring diagram
- water pump wiring diagram single phase
Frequently asked questions
What does the float switch symbol mean in a circuit diagram?
The float switch symbol represents a liquid-level-sensing switch that automatically opens or closes its contacts based on whether the liquid surface is above or below a setpoint. It is used in circuit diagrams wherever a pump, valve, or alarm must respond to liquid level without manual operation.
What does the float switch symbol look like?
The float switch symbol looks like a standard single-pole switch contact (a diagonal line crossing a gap between two terminals) with a circle or oval attached to the actuating bar to represent the buoyant float. The two connection points are labelled In (in) and Out (out).
What is the difference between a normally-open and normally-closed float switch?
A normally-open (NO) float switch has contacts that are open when the float is in its rest (low-liquid) position and close when the liquid rises to actuate the float. A normally-closed (NC) float switch has contacts that are closed at rest and open when the liquid rises. The choice depends on whether the load must energise or de-energise on high level.
What is the designator letter for a float switch on a schematic?
The designator for a float switch is typically S (switch) or LS (level switch), followed by a reference number such as LS1 or LS2. In industrial P&ID drawings, the instrument tag may use the ISA-5.1 designation LT (level transmitter) or LSH/LSL for high and low level switches.
Which standard defines the float switch symbol?
The float switch symbol is defined under IEC 60617-07, which covers binary switches and their actuator qualifiers. In North America, ANSI Y32.2 / IEEE 315 provides the equivalent representation using a labelled actuator on a standard switch contact.
How do I wire a float switch to control a pump?
Connect the hot (line) conductor to the In (in) terminal of the float switch and the Out (out) terminal to the motor contactor coil or directly to the pump motor hot terminal. The neutral connects directly to the motor. When the float rises to the trigger point, the switch closes, completing the circuit and starting the pump.
What are typical voltage and current ratings for float switches?
Standard float switches are rated 5 A to 15 A at 120 V AC or 250 V AC for residential and light-commercial use. DC variants are rated 1 A to 10 A at 12–48 V DC. High-capacity industrial float switches may carry ratings up to 30 A at 480 V AC.
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