Deciding whether having a normally open float switch or a normally closed float switch for pump control can be a little confusing. At Automation Products Group, Inc. (APG), we’ve provided the ultimate guide to configuring a float switch.
When purchasing a float switch, most of them have normally open or normally closed operation. This refers to the completion of an electrical circuit. An open circuit is incomplete because the electric current can’t complete the loop due to a gap. A closed circuit is complete without any gaps, enabling the current to travel through the whole loop.
With level switches, these circuits are opened and closed by the float either moving up or down based on the rising or falling level of the liquid. “Normally” refers to the lowest position of the float when at rest. “Open” means an open circuit, which is off. “Closed” switch completes a circuit, turning it on. Consider if rising or falling liquid levels trigger an action, and whether that action turns a circuit on or off. A normally open switch doesn’t allow any electricity through it when the float is freely hanging. As the water flows into a tank and raises the float, its contacts will close and turn on an emptying pump.
Deciding Float Switch Configuration
Deciding if a normally open float switch or normally closed float switch is needed is determined by what the switch does when the float is at rest. At rest means that float isn’t suspended in liquid. In terms of switches, normal refers to a float at rest.
When the float is at rest:
- If the switch needs to be energized or on, a normally closed float switch is needed.
- If the switch needs to be de-energized or off, a normally open float switch is needed.
Normally open switches are typically used for pumps that empty a tank, while normally closed switches are typically used for pumps that fill a tank.
Let us know if you need help deciding whether you need a normally open float switch or normally closed switch. Our Measurements Experts will be happy to help.
WRITTEN BY
Sami T.
Sami Thompson is APG’s Marketing Technical Writer and has been with the company since 2022. With a master’s degree in English from Utah State University and a 40-page thesis publication under her belt, Sami has a demonstrated strong writing background. In her free time, Sami enjoys reading and birdwatching.