How to wire a float switch

How To Wire a Float Switch

Float switch

Figure 1: Float switch

A float switch detects the level of liquid in a tank or container. Properly installing and wiring the float switch is crucial to ensure the switch works correctly. This article discusses how to wire a water tank float switch, but the same mechanism is applicable for wiring float switches in other media as well.

Table of contents

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Float switch installation

A float switch floats on a liquid surface and moves vertically up or down as the liquid level changes within the tank. The switch is capable of sending a signal to trigger a motor to fill the tank, a valve to open and empty the tank, a high water level alarm, or both depending on the media level within the tank. Read our article on float switches to learn more about how a float switch works.

A float switch consists of a buoyant case, a switch, and an electrical wire. Figure 2 shows how to position the wire and the float switch so that the wire doesn’t change the switch’s depth. Fix the float switch to a bracket on the water tank's wall or along the pipe running down inside the tank.

Figure 3 shows float switch installation with a counterweight. It is important that there are no obstructions below or above the float switch that it could get stuck on as it moves with the water level. The depth, or length of the cable, between the fixture point of the float switch and bracket determines the total extension of the float and the consequent distance water must rise or lower for the pump to start or stop.

Proper installation of a float switch. Bracket (A), Pipeline (B), Link (C)

Figure 2: Proper installation of a float switch. Bracket (A), Pipeline (B), Link (C)

Float switch wiring

Figure 3 shows an installation example of a float switch with a counterweight. The float switch functions in two states (high or low) based on the liquid level in the tank. The switch can perform different functions depending on its wiring. It is typically wired to have one operation, like filling a tank, emptying a tank, or triggering a high-water alarm.

  • Filling application: The float switch tells the pump to stop when the switch is at the high point and turn it on when the switch is at the tank bottom.
  • Emptying application: The float switch tells a valve to open when the switch is at the high point and close when the switch is at the tank bottom.
Float switch states

Figure 3: Float switch states

MAC float switch wiring

MAC3 provides reliable and high-quality float switches. These series are available for a wide range of applications from clean non-turbulent water, sewage systems, to turbulent water. MAC3 float switches function either in normally open (NO) or normally closed (NC) states.

  • Normally open (NO) float switch: The electrical circuit within the switch remains open when the switch is down and closed in the ‘up’ position. So, the switch is open with gravity pulling it down and closes as the liquid level rises to the pre-set level.
  • Normally closed (NC) float switch: The electrical circuit within the switch remains closed when the switch is at the bottom and open in the ‘up’ position. So, the switch is closed with gravity pulling it down and opens as the liquid level rises to the pre-set level.

Note: The ‘normal’ operation may differ for different float switch brands and types. Read the brand’s manual on how to wire it in either configuration.

Float switches can also function as single-function or double-function (changeover contact) switches.

Single-function float switch

Single-function float switches are either NC or NO, and they have a common and ground wire. Ensure to properly ground the ‘GROUND’ wire in a single-function float switch.

Single-function MAC float switch wiring with emptying (left) and filling (right) applications, respectively.

Figure 4: Single-function MAC float switch wiring with emptying (left) and filling (right) applications, respectively.

Double-function (dual) float switch

Double-function float switches have an NO, NC, and common wire. Insulate the wire that is not used in a double-function float switch.

Double-function MAC float switch wiring with emptying (left) and filling (right) applications, respectively.

Figure 5: Double-function MAC float switch wiring with emptying (left) and filling (right) applications, respectively.

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