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Switch Definitions

  • Pole:  Number of contact sets on the switch.    This describes the number of electrical circuits that can be switched.  A light switch is a single pole switch because it switches one circuit.
  • Throw:  The number of "throws" is the number of electrical connections the switch can make. The simplest switch is single throw - either it connects to the other end of the circuit, or not. But there are many other possibilities, such as a "double throw" switch that can channel electricity into either of two places.  
  • Way:  Number of conducting positions – when there are three or more choices for directing power then the term WAY is used in lieu of throw.  If a switch can make 3 connections then it is defined as a 3 way switch.
  • Momentary:  When a switch is described as a momentary switch it is a switch that only works as long as you press on the switch.  Think of a automobile horn button.  When you press the horn button, the horn sounds.  The sound continues as long as you have the button pushed.  When you release the button the horn stops.   The door bell button at your front door is a momentary switch.
  • Open: Off position.  Think of the basic switch of two wires.  If the wires are not connected the switch is open.
  • Closed:  On position – contacts are conducting (there could be more than one "on" position)
  • Normally Open (NO) - Applies to Momentary Switches.   A normally open Momentary switch is only closed when the button is pushed.  When you release the button the circuit opens.  An automobile horn button is a normally open momentary switch.  A "normally open" switch lets electricity flow only when it is activated. When the switch is left alone (the "normal" condition), it "opens" up, stopping the flow of electricity.
  • Normally Closed (NC) Momentary Switch.  A normally closed momentary switch is only  off or "open" when the switch is pushed.  An example of a normally closed switch could be the switch that turns the light on in your refrigerator when you open the door.  When you close the door the switch is pushed and the circuit is opened thus turning off the light.  When you open the refrigerator door the switch returns to it's normally closed ("on") position and the light comes on.  A "normally closed" switch works just the opposite of a "normally open" switch.  When a "normally closed" switch is sitting idle, electricity flows through it. When you actuate the switch, the flow stops.