40
Normally Closed
Activation Arm
Press this lever down
to activate the switch
Common
Normally Open
Three prongs are present on a limit switch. They are labeled Common or “Com”; Normally Open, abbreviated NO; and
Normally Closed, abbreviated NC. Below is a wire diagram of a limit switch.
When no pressure is applied to the limit switch activation arm, electricity will fl ow from the Common prong to the
Normally Closed prong.
When the activation arm is pressed, electricity will fl ow from the Common Prong to the Normally Open Prong.
Electricity will never travel from the NO prong to the NC prong.
The word “NORMALLY” generally refers to the action of the switch when nothing is activating it. “Normally Closed”
is a continuous fl ow of electricity when the switch is not activated, establishing a closed circuit. “Normally Open” is a
non-continuous fl ow (no fl ow) of electricity when the switch is not activated, establishing an open circuit.
Activation arm IS being pushed
Common
Normally Open
Normally Closed
D
Basic Electrical Information
Limit Switches
Common
Normally Open
Normally Closed
Activation arm IS NOT being pushed
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