How to Use Float Switch: Examples, Pinouts, and Specs

A float switch is a device used to detect the level of liquid within a tank or reservoir. It operates by using a buoyant float that rises and falls with the liquid level, triggering an electrical switch to open or close a circuit. Float switches are widely used in applications where liquid level monitoring and control are essential.

• Water level monitoring in tanks and reservoirs
• Automatic pump control for filling or draining tanks
• Liquid level alarms in industrial processes
• Monitoring and controlling sump pumps
• Preventing overflow or dry-run conditions in water systems

Below are the key technical details for a typical float switch. Specifications may vary depending on the specific model.

Float switches typically have two or three wires for connection. The table below describes the wiring configuration:

Note: Some float switches may only have two wires (Red and Black), in which case they operate as either NO or NC depending on the orientation.

1. Determine the Contact Type: Identify whether the float switch is Normally Open (NO) or Normally Closed (NC). This information is typically provided in the product datasheet.
2. Connect the Wires:
   • For a two-wire float switch, connect one wire to the power source and the other to the load or control circuit.
   • For a three-wire float switch, connect the Red wire to the power source, and use either the Black (NO) or Blue (NC) wire depending on your application.
3. Position the Float Switch:
   • Install the float switch in the tank or reservoir at the desired liquid level.
   • Ensure the float can move freely without obstructions.
4. Test the Circuit:
   • Simulate changes in liquid level to verify that the float switch operates as expected.
   • Check for proper switching of the circuit (open or close) when the float moves.

• Orientation: Ensure the float switch is installed in the correct orientation (vertical or horizontal) as specified by the manufacturer.
• Liquid Compatibility: Verify that the float switch material is compatible with the liquid being monitored.
• Electrical Ratings: Do not exceed the voltage or current ratings of the float switch to avoid damage or failure.
• Debris and Contamination: Keep the float switch clean and free from debris to ensure reliable operation.
• Safety Precautions: Always disconnect power before installing or servicing the float switch.

Below is an example of how to use a float switch with an Arduino UNO to monitor water levels and control an LED.

• Connect the Red wire of the float switch to the 5V pin on the Arduino.
• Connect the Black wire to a digital input pin (e.g., pin 2) on the Arduino.
• Use a pull-down resistor (10kΩ) between the input pin and ground.

// Float Switch Example with Arduino UNO
// This code monitors the float switch and turns an LED on or off based on the
// liquid level.

const int floatSwitchPin = 2; // Pin connected to the float switch
const int ledPin = 13;        // Pin connected to the onboard LED

void setup() {
  pinMode(floatSwitchPin, INPUT); // Set float switch pin as input
  pinMode(ledPin, OUTPUT);        // Set LED pin as output
  digitalWrite(ledPin, LOW);      // Turn off LED initially
  Serial.begin(9600);             // Initialize serial communication
}

void loop() {
  int floatState = digitalRead(floatSwitchPin); // Read float switch state

  if (floatState == HIGH) {
    // Float switch is triggered (liquid level high)
    digitalWrite(ledPin, HIGH); // Turn on LED
    Serial.println("Liquid level HIGH");
  } else {
    // Float switch is not triggered (liquid level low)
    digitalWrite(ledPin, LOW);  // Turn off LED
    Serial.println("Liquid level LOW");
  }

  delay(500); // Wait for 500ms before next reading
}

1. Float Switch Not Triggering:

   • Cause: Incorrect wiring or loose connections.
   • Solution: Double-check the wiring and ensure all connections are secure.

2. Switch Stuck in One Position:

   • Cause: Debris or contamination around the float.
   • Solution: Clean the float and ensure it moves freely.

3. Incorrect Liquid Level Detection:

   • Cause: Improper installation or orientation.
   • Solution: Reinstall the float switch according to the manufacturer's instructions.

4. Float Switch Damaged:

   • Cause: Exceeding voltage or current ratings.
   • Solution: Replace the float switch and ensure the circuit operates within the specified ratings.

Q1: Can a float switch be used with corrosive liquids?
A1: Only if the float switch is made of materials compatible with the corrosive liquid. Check the product specifications.

Q2: How do I know if my float switch is Normally Open (NO) or Normally Closed (NC)?
A2: This information is typically provided in the product datasheet. You can also test the switch with a multimeter.

Q3: Can I use a float switch to control a high-power pump?
A3: Float switches are usually rated for low currents. Use a relay or contactor to control high-power devices.

Q4: What happens if the float switch cable is too short?
A4: You can extend the cable using waterproof connectors, but ensure the connections are secure and insulated.