Apprentice path · Stage 10: Devices and terminations · Lesson 34

Switches control paths

A switch does one thing: it opens or closes a conductive path. It does not make electricity.

Why this matters on the job

Beginners talk about a switch "turning the power on", and that mental picture leads straight to assuming a switch in the OFF position means nothing downstream is live.

How to think about it

  1. A switch opens or closes a conductive path -- that is its entire job.
  2. Pole and throw describe its connections: how many paths it controls, and how many positions each can take.
  3. The device rating has to suit the application it is used in.

Worked through

Picture a source, a switch and a lamp in a loop. Close the switch and the loop is complete, so current flows and the lamp lights. Open it and the loop is broken, so it does not. The source voltage was there the whole time, before and after -- the switch never created it and never removed it. All that changed was whether there was a path.

Check yourself: A switch is open and the lamp is off. Is the source voltage gone?

Answer: No. A closed switch can complete a path; it does not create the source voltage, and an open one does not remove it.

The switch controls the path, not the source. Breaking the path stops current flowing through the load, but the supply is still sitting there on the line side of the switch.

Watch out for: Reading "off" as "dead". An open switch means no current through the load. It says nothing about what is live on the other side of that switch.
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Written from the owner's poster for this lesson. Nothing added beyond what the poster states.

Written for Texas apprentices as free study material. The Texas apprentice licence is an application, not an exam (Occupations Code 1305.161), and nothing here counts as apprenticeship hours or continuing-education credit. VoltMark is not affiliated with, endorsed by, or sponsored by NFPA, PSI, TDLR, or any state or local licensing authority. Always follow your employer's safety programme and your supervising electrician.