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SESK: Stuff Everyone Should Know · sesk.info/ham-spdt-switch-function

What is the function of an SPDT switch?

A single circuit is switched between one of two other circuits.

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  1. A single circuit is opened or closed
  2. Two circuits are opened or closed
  3. A single circuit is switched between one of two other circuits ✔

Why: SPDT means single-pole, double-throw. It connects one common circuit to either of two other circuits.

Huh, didn't know that: A three-way household light switch is a familiar SPDT application.

The dad joke
Why is an SPDT switch great at picking dinner? It always chooses one of two options.
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References

Answer: A single circuit is switched between one of two other circuits. SPDT means single-pole, double-throw. It connects one common circuit to either of two other circuits.

  1. NCVEC 2026-2030 Technician Question Pool, T6A08 ncvec.org/downloads/2026-2030%20Technician%20Pool%20and%20Syllabus%20Public%20Release%20Feb%2019%202026.pdf
    C. A single circuit is switched between one of two other circuits
    Checked 2026-10-09.

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