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SPDT Switch Wiring: Everything You Need To Know

With technology advancing quickly in the 21st century, there are plenty of electronic components and topics out there that you can research. However, in this blog post, you will learn what SPDT switch wiring is and how to apply it.

So let’s dive into answering the first question on your mind. 


What Is an SPDT Switch?


SPDT stands for single pole double throw switch, which is a single input with two different output switches. With SPDT, unlike the other switch varieties, you can control two circuits with the same single input. 

SPDT switch wiring is administered through two options. A) the manual method or b) integrating it within the electromagnetic coil. 


Types of Switches


There are four common types of electrical switches, listed here:

  • SPST (single pole, single throw)
  • SPDT
  • DPST (double pole, single throw)
  • DPDT (double pole, double throw)


Pole and Throw Definitions


These terms describe switch contact variations. Although these definitions can get technical and will not be used often in this article, you should know that the number of poles corresponds with the number of electrically separate switches, controlled by one physical actuator, a device that causes other devices to operate. 

Contradictorily, the number of throws is the number of separate wiring path choices.

Think about it this way. SPDT connects one of the two terminals to the common terminal because it is a single-pole, double-throw.  


How Does an SPDT Switch Work?


SPDT Schematic Symbol


An SPDT has a 3 pin toggle switch connection with two abilities: on-on or on-off-on. The on-on option has two positions; a connection is formed from either A to B or A to C. 

For example, say A is the signal. The connection flows to B or C. So, C is not connected when A is with B. Just like B is not connected when A is with C. You can program an SPDT to work however you want, but you want to generate digital signals from power sources. These switches are inexpensive as well.

Also, SPDT switch wiring can have three positions, where neither is connected. Therefore, you can have two active positions, like an on-off switch, or none at all. 

Another way to better understand this would be to designate A as one of the common terminals. A connects to a specific source. B connects to the first circuit, and C connects to the second. Then, A connects to either switch terminal.

If A is attached to B, then the current flows from the source to B and will be turned on when you operate the SPDT switch and vice versa; if the C circuit receives the power, then B will be turned off.


SPDT Applications


  • ABB/Siemens VFDs
  • Control Circuit 


  • PLC output switches
  • Selector switches (the single common configuration)


How to Wire an SPDT Switch


Did you know that the SPDT switch varies in design depending on the location? In Britain, SPDT is a two-way switch, whereas, in North America, it is a 3-way switch. This section will break down how to wire an SPDT and how to approach its multiple functions.




The light or lights in your residence can be controlled by more than one switch, yet, the tendency when builders construct a home is to use three-way switches, and the electrician prefers an SPDT switch the majority of the time. 

To control light with two or more switches, they must create a complete electrical circuit for the energy current to flow. Then, the bulb will light up if the switches are turned on, and the wiring circuit is completed. Similarly, if both switches are down, the circuit is complete. 

Nonetheless, if one switch is up and the other is down, the current reaches an end. Therefore, no current flows, and the bulb will shut off.


Three or More Switches, Wiring, and the National Electric Code


To control light with three or more switches involves a complicated process that is elaborated below. When dealing with more than two switches, one or more four-way switches are added between the three-way switches.

Remember that four-way switches have two positions; the first being the contacts are connected straight through, resulting in no effect. However, if the switches cross and connect with the contacts on the left and right (forming an ‘X’ shape), the light can be placed anywhere in the return wire or between any pair of switch boxes and will work successfully.

For more help or a visual representation of this process, consult an SPDT switch diagram.

When wiring a multi-switch circuit, be sure to use two-conductor (or black and white) cables from the panel to the first switch. White represents a neutral wire and is the current-carrying wire bonded to the ground in a circuit breaker panel (or distribution board). Black and red mean hot conductors.

The National Electric Code (NEC) allows some exceptions; it is more effective to place a light between two switches or between a panel and the first switch. A typical two-conductor or three-conductor can generate electricity. Despite that, be cautious, since confusion can occur. Use a black marker to signal any hot white wire. 




Four-way switches are voluntary since you only need two switches. You have the option to neglect both four-way options. Yet, you can also add as many four-way switches as you like in place of certain other ones. 

If you make these adjustments, label the wires correctly, informing anyone working that the wire could occasionally deliver 120 volts. Additionally, the worker can then wire and replace any necessary cables when informed properly.




Even though SPDT toggle switch wiring may seem intimidating at the moment, with the knowledge you have now after reading this article, you hopefully feel more confident when tackling a home project involving these connections.

As previously stated, technology is constantly improving, and new possible theories, such as free energy, are quickly becoming more of a reality. For now, focusing on finding answers to your current wonders of SPDT will help you achieve whatever electrical goals you have in mind because of its versatility.