SPDT Magnetic Switches Explained: Flexible Control for Industrial Applications
In modern industrial automation and control systems, flexibility, reliability, and longevity are crucial. That’s where SPDT (Single Pole, Double Throw) magnetic switches shine. In this post, we’ll break down how SPDT magnetic switches work, their benefits, where they’re applied, and how MagneLink’s solutions bring real value to industrial systems.
What Is an SPDT Magnetic Switch?
An SPDT magnetic switch (also called a changeover magnetic switch) features one input (pole) and two possible outputs (throws). The switch connects the input to either of the two outputs depending on the presence or absence of a magnetic field.
- Pole: The common terminal, or input.
- Throws: Two output terminals (often NC = normally closed, and NO = normally open).
- Operation: When a magnet comes within the activation range, the internal reed or solid-state mechanism (depending on the switch type) shifts the connection from one throw to the other.
This arrangement allows a single magnetic detection device to toggle between two circuits—making SPDT switches more versatile than simple on/off (SPST) magnetic switches.
Why Choose SPDT Magnetic Switches?
1. Greater Control Flexibility
With SPDT, you can route signals or power to different circuits depending on the state. For example, one throw might shut off a process while the other activates a backup system.
2. Built-In Redundancy & Monitoring
Because both outputs are available, you can monitor one throw while the other is active, improving safety and diagnostics.
3. No Physical Contact (Non-Contact Actuation)
Like all magnetic switches, SPDT versions are actuated magnetically—meaning fewer mechanical parts, reduced mechanical wear, and improved durability in harsh environments.
4. Wide Application Range
SPDT magnetic switches can be built using reed, Hall effect, transistor, or triac sub-switch designs, making them suitable for both light and heavy (inductive) loads, AC or DC circuits. MagneLink offers SPDT designs across housing types.
Technical Variants & Considerations
When specifying an SPDT magnetic switch, consider:
- Switching Technology
- Reed switches (dry contact) for AC or DC light loads
- Hall effect sensors for solid-state switching in DC circuits
- Transistor or Triac variants for heavier loads or inductive applications
- Voltage & Current Ratings
Ensure the switch can handle the maximum voltage and current of your system. For instance, MagneLink’s MLT-Exx SPDT design uses a 100 VA Reed, so you want to keep the combination of voltage and current in your switched circuit below the 100 VA threshold to maximize the switch’s lifespan. - Housing & Environmental Robustness
Housing materials (glass-filled nylon or aluminum) can be chosen based on user preference. The housing shape and style also affects how it is mounted in the system (flush, threaded, dovetail, etc.). - Actuation Distance & Field Strength
The switch must be activated reliably by the magnet under expected operating tolerances (gap, alignment, field strength). - Lead/Cable Options & Shielding
Cable length, shielding, and flexibility may be critical in industrial environments.
Real-World Applications of SPDT Magnetic Switches
SPDT magnetic switches find utility across many industrial contexts:
| Application | Use Case |
| Redundant control systems | Switch between primary and backup circuits automatically |
| Automation & robotics | Route signals to different actuators or end-of-travel detection |
| Elevator/door systems | Detect and control door open, closed, or locked states |
| Safety interlocks | Switch between safe / unsafe pathways or redundant circuits |
| Power source switching | Change between primary and alternate power feeds non-disruptively |
| Fluid level control & alarms | Switch between normal and alarm circuits depending on level sensors |
Because there’s no physical contact, SPDT magnetic switches perform reliably even in environments with dust, oil, vibration, or moisture.
How MagneLink Leverages SPDT Magnetic Switches
At MagneLink, SPDT configurations are built into many of our magnetic switch product lines. For example:
- The MLH series includes SPDT reed options in small housings for tight spaces.
- The MLT series supports SPDT as part of its reed, triac, or transistor switch options—useful in AC or DC systems with varying loads.
- Our broader magnetic switch catalog supports custom SPDT designs in various housings, materials, and sub-switch types to suit your application.
We’re also able to provide custom solutions when standard options don’t quite fit your system parameters.
Design Tips & Best Practices
- Match the switch to the load
Don’t oversize or undersize the switch—select one rated appropriately for your circuit. - Consider magnet strength & gap tolerance
Provide enough margin so the switch reliably actuates in real-world conditions. - Use proper mounting and shielding
Prevent stray magnetic fields and ensure precise alignment. - Plan for diagnostics / monitoring
Leverage both throws (NO & NC) to monitor system health or redundancy. - Factor in temperature, vibration, and environment
Use robust housings and cable protections where needed.
SPDT magnetic switches offer a powerful combination of flexibility and reliability for industrial control systems. They allow you to route signals or power between two states, add redundancy, or monitor system health — all while avoiding mechanical wear through magnetic actuation.
If you’re evaluating SPDT switches for an industrial application — whether automation, safety, or control systems — MagneLink, Inc. can provide both standard and custom solutions. Visit our Magnetic Switches page for more details or contact our team to discuss your specific requirements.