Micro Limit Switches

What is a Micro Switch?

"Micro switch" is actually a trademarked name people use to refer to snap-action switches in general, much like how people use Kleenex as a general term for paper tissues. The term "snap-action" refers to the instant when the contacts suddenly change state.

Micro switches are widely used for a wide variety of applications. For example, most limit switches are snap-action.

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How does a Micro Switch Work?

The key feature of micro switches is the use of an over-center, or tipping-point, mechanism to create specific operating (trip) and release (reset) points where the contacts will change state.

Micro Switch Terminology

An operating or trip point is where the contacts change state from their normal, unoperated position.

A release or reset point is where the switch contacts return to their normal position.

Differential travel refers to the distance between the operating and release point.

The purpose of separating the operating and release points is to protect the contacts from rapid, undesirable ON/OFF due to vibrations that will shorten the operating life of your switch.

Over-travel is a built-in safety feature that prevents damage to the switch by allowing the actuator to travel beyond its operating point.

To help minimize mechanical stress and damage, you should make sure the actuator does not go beyond the allowed over-travel distance.

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Advantages of Using a Micro Switch

Precise Performance

Unlike other types of switches where any actuator movement will cause the contacts to move, the contacts in a micro switch will not change state until the actuator reaches a specific trip or reset point along its range of motion.

Fast Switching Speeds Reduce Arcing Damage

Switching speed, in electromechanical switches, refers to how fast contacts open and close. High switching speeds help extinguish arcs faster, which lessens damage to contact surfaces caused by arcing.

Reliable Switching

The speed and movement of the contacts do not depend on the speed and movement of the actuator. Thus, Unless a switch is near the end of its operational life, you can count on the contacts changing state in a predictable manner.

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How to Select a Micro Switch

The following specifications have to do with micro switches in particular. For general selection factors to consider, see How to Select an Electrical Switch.

Actuator Type

For example, do you want to use a push button, lever, pin, or roller? How long or short do you need the actuator to be? How big or small (e.g. roller vs. pin)?

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Electrical Ratings

As always, the first step is to figure out what kind of supply power you will be using for your switch. Is your power supply AC or DC?

At what voltage?

What is the largest current the contacts will have to switch?

Pole and Throw Count

The number of movable contacts you require determines how many poles you need in a switch.

The number of fixed contacts determines how many throws, also called "way," you need.

Number of N.O. and N.C. Contacts

Normally open (N.O.) contacts remain open in their untriggered state and close when actuated. In contrast, normally closed (N.C.) contacts remain closed and open when actuated.

Enclosure

What kind of environment will the switch be operating in? Your enclosure will need to have the proper IP or NEMA rating to protect the switch from conditions of the operating environment (e.g. water, explosion hazard, etc.).