What is SPDT Micro Switch? A Complete Guide for Beginners

2025-05-28

Widely used in consumer electronics, industrial controls, appliances, and automotive systems, SPDT micro switches combine precision actuation with high durability. This guide will introduce you to the basics of SPDT micro switches as opposed to DPDT switches and answer frequently asked questions. It's worth a look for beginners and engineers alike!

What is SPDT Micro Switch？

SPDT micro switch is a types of micro switch, using a pre-loaded micro-spring mechanism, the contacts switch instantly when reaching the set travel (Operating Position), with quick action and very short contact transition time, thus reducing arcing and jitter.

Structure

Three-terminal design

Including a common terminal (COM), a normally closed terminal (NC, Normally Closed) and a normally open terminal (NO, Normally Open). In the initial state, COM is connected to NC; when the actuator lever is pressed or pushed beyond the operating force point, COM will switch to NO instantaneously.

Various actuator forms

Commonly, there are Standard Lever, Roller Lever, Plunger, Hinge Lever and Wobble Stick, etc., which can be selected according to the installation space and action mode.

Spring-loaded Snap Action Construction

Inside the micro switch there is a static contact, and a movable contact connected to a spring. When the actuator is activated, the preload spring stores energy until the movable contact reaches a critical point. At the operating point, the movable contact suddenly switches the contact from NC to NO within a few millimeters of travel.

Principle of operation

In the stationary state, COM is connected to NC. When the actuator is pressed beyond its working point, the snap-action spring flips, connecting COM to NC or. When the actuator is released, it snaps back to the NC connection. The opposite is true if COM is connected to NO.

Benefits of SPDT Switches

High sensitivity and precision: The snap action mechanism actuates within very small displacements (<0.5 mm), ensuring that even small displacements of the actuator can reliably change the contact state.

Long Mechanical and Electrical Life: Micro switches are typically rated for millions of mechanical cycles and hundreds of thousands of electrical cycles at rated currents, thanks to fast contact changes that minimize wear and arcing.

Compactness: Micro switches are typically less than 20 × 10 × 6 mm, in size and can be integrated into small assemblies, making them ideal for consumer electronics, automotive modules, and industrial sensors.

Low Cost: The SPDT is a standard type of micro switch, and most manufacturers have production processes and standards that allow for high volume production, effectively reducing your costs. At the same time, the long life of the micro switch allows for effective product life and reduces changeover costs.

Disadvantages of SPDT Micro Switch

Limited Current/Voltage Ratings: Typical contact ratings range from 1 A up to around 10 A at low voltages; higher-power applications require larger, more expensive switches or external relays.

Affected by the environment: Not all micro switches are completely hermetically sealed, so some will degrade in performance when exposed to dust, moisture or corrosive environments.

Unavoidable wear: Micro switches are subjected to long term cycling and actuation, inevitably the brakes or contacts will wear out and need to be replaced periodically.

Types of SPDT Micro Switch

Standard Lever SPDT Micro Switch: A basic limit switch，Commonly used in a variety of products, such as washing machine door interlocks, machine arms and so on.

Roller levers SPDT Micro Switch: Lever with rollers, often used at the end of the conveyor stroke.

Pin plungers SPDT Micro Switch: Vertical plunger with small stroke Linear position detection, safety gate.

Hinge Lever SPDT Micro Switch: Low actuating force, long levers that pivot at one end, primarily used in long travel applications.

Application

Consumer Electronics: SPDT micro switches are commonly used in consumer electronics such as mouse buttons, stereos, printer feed sensors, vending machine selector switches for power switching or audio selection.

Automotive Systems and Household Electrics: SPDT micro switches are also used as detection switches for door latch detection, gear shift position sensors, microwave oven door interlocks and washing machine lid sensors.

Industrial Equipment: In industrial equipment, SPDT micro switches are often used as CNC limit switches for detect end‐of‐travel on linear actuators, conveyors, or robotic arms and route the signal accordingly.

Difference of SPDT Switch and DPDT switch

Feature	SPDT Switch	DPDT Switch
Poles	single circuit	two independent circuits
Throws	NO and NC	2 per pole (4 total)
Terminals	3 terminals (COM, NO, NC)	6 terminals (COM1, NO1, NC1, COM2, NO2, NC2)
Functionality	Route one input between two outputs	Route two inputs between two outputs; can reverse polarity for one circuit
Size & Cost	Smaller, less expensive	Larger, more expensive
Typical Use	Simple on/off or source-select	Dual-circuit switching, motor forward/reverse control

How to choose the switch?

If only one circuit needs to be switched between two states, use the SPDT switch - it's simpler, cheaper and more compact.
If two circuits must be switched at the same time (e.g., polarity reversal or routing a two-channel signal), use a DPDT switch without adding additional relays or wiring.

FAQ

Q1: Can I use an SPDT micro switch for high-power applications?

Not directly. For currents above 10 A or voltages above 250 VAC/48 VDC, pair the micro switch with a relay or contactor that is rated for your load.

Q2: How long do SPDT micro switches last?

Electrical life: Often 1–10 million cycles (no load).

Mechanical life: Typically 100,000–1,000,000 cycles under rated load.

Environmental factors (temperature, dust, humidity) and load type (resistive vs. inductive) will affect lifespan.

Q3: How do I choose between a roller lever and a pin plunger?

A: Roller levers are best for cam or sliding-surface actuation, reducing friction and wear. Pin plungers suit straight-line actuation with minimal over-travel.

Q4: What actuator force do SPDT micro switches require?
A: Actuation force varies by model (typically 100–500 gf). Check the datasheet’ s Operating Force (O.F.) and Release Force (R.F.) values to match your application.