Different Types of Float Switches and What They Do
In this article, we’re going to review the basics of float switches. We’ll cover the difference between:
- Pump switches vs. control switches
- Normally open vs. normally closed
- Mechanical vs. mercury floats
- Specialty floats
- And the colored caps on select mechanical control switches
Let’s get started!
Pump vs. Control Switches
Pump switches are used to directly control a pump. They are wide-angle, meaning they have to tip up and down farther than a control float to turn on or off. The tether length is how much cable is between the float body and the cable weight, or cable clamp. This will determine the pumping range, or the distance between the points where the switch will turn on and off.
Pump switches are designed to carry higher amps than control switches. You can visit our float catalog pages on our website for each model’s specifications.
Pump switches are available with or without a piggy-back plug. To install a pump switch with a piggy-back plug, you simply plug the float switch into a power outlet, and then plug the pump into the piggy-back plug. Pump switches without a piggy-back plug must be hard wired.
Pump Switches are available in pump up, pump down, or SPDT configurations. Pump up is used to fill a tank and pump down is used to empty a tank. An SPDT is a 3-wire float that can be wired to be used as either pump up or pump down.
Control switches are typically narrow-angle, meaning they only need to move slightly above and below horizontal to turn on and off. This means they are sensitive to small changes in the water level. They are used in conjunction with tank alarms or control panels to perform functions such as providing input to a pump controller or alerting of a threatening liquid level condition. SJE Rhombus also offers several wide-angle control switch models.
Control switches are designed to carry lower amps than pump switches. They should not be used to carry full load current of a pump. Consult our catalog for full specifications.
Normally Open vs. Normally Closed Float Switches
Depending on what the float switch is being used for, it’s contacts may be normally open or normally closed. If the float switch contacts are closed when the float is hanging down it is a Normally Closed (N.C.) switch. If the contacts are open when the float is hanging down it is a Normally Open (N.O.) switch. An SPDT float is a 3-wire float switch that can be wired either Normally Open or Normally Closed.
Normally open contacts are used in applications such as emptying tanks or notifying of high-water level conditions. This means the switch will be inactive when it is in the lowered position and activated when raised. Normally open contacts are the most common kind you’ll find in the septic system industry.
Normally closed contacts are used in applications such as filling tanks or notifying of low water level conditions. This means the switch will be inactive in the raised position and active in the lowered position.
Mechanical vs. Mercury Float Switches
Float switches use either a small amount of liquid mercury or a mechanical mechanism to open and close the contacts. SJE Rhombus offers both types of pump and control switches to suit your needs.
Before choosing a float switch, you’ll want to check your local mercury legislation, as many areas restrict the sale of mercury products. We also have a conversion chart on our web site to help you replace a mercury switch with an equivalent mechanical switch solution.
Other Float Types
There are a few other types of floats that SJE Rhombus offers with special features. The first are potable water switches. These switches are safe for use in drinking water applications. For pump switches, our SJE PumpMaster® WPS is a mechanically-activated, wide-angle switch that is suitable for potable water applications. For control switches, our SJE MilliAmpMaster® WPS is a mechanically-activated, narrow-angle switch that offers reliable low current control for AC and DC potable water applications.
Another special type of float is designed to withstand higher than normal temperatures. Our SJE HiTempMaster™ is a mechanically-activated, wide-angle pump switch that is designed specifically for high temperature sump applications up to 200°F.
Mechanical Control Switch Cap Colors
Several of our control switches share the same sleek design. We have added colored caps for easy identification:
- Yellow: SJE SignalMaster® Normally Open
- White: SJE SignalMaster® Normally Closed
- Green: SJE SignalMaster® SPDT – Single Pole, Double Throw which means they can be wired to work in either normally open or normally closed applications.
- Blue: SJE MilliAmpMaster®, narrow or wide angle
- Orange: SJE MilliAmpMaster® WPS for potable water applications
All float switches are available in a variety of cable lengths to suit your application and backed by our industry-leading five-year warranty.