Three-way switch
One of a pair of switches that control the same light from two places. Plans mark it S3.
Easily confused with
How to read it
The Army's print-reading manual describes a three-way switch circuit as one that controls a single outlet from two locations, and says the switch appears on an electrical plan as the symbol S3. NECA 100 lists the three-way switch after the single and double pole switches and before the four-way switch. The Navy's Engineering Aid course gives the typical case: one switch at the head of a stairway and the other at the foot.
Also searched as: 3-way switch, S3.
This explains what a symbol represents on a drawing. Conventions vary between firms and standards, and a drawing's own legend takes precedence.
Look-alikes
A plain S is a single-pole switch, which controls a light from one place.
Read next
- Next in Blueprint symbolsCeiling lightA light fixture on the ceiling. The circle marks where it goes; letters and numbers beside it can give the fixture type and circuit.
- The same shape in US state flagsFlag of IndianaIndiana’s flag is a gold torch on blue inside a circle of 19 gold stars, with INDIANA arched over the largest star. Under the state law, the 13 outer stars are the original states, the five inner stars the states admitted before Indiana, and the large star above the flame Indiana itself; the Indiana Historical Bureau says the torch stands for liberty.
More blueprint symbols
The same shape elsewhere
Browse symbols drawn with letters and numbers.
Sources
- Symbols for Electrical Construction Drawings, NECA 100-2013 (ANSI), National Electrical Contractors Association (Internet Archive copy), sec. 4.0, symbol 4.003
- Construction Print Reading in the Field, TM 5-704 / AFM 85-27, Departments of the Army and the Air Force, para. 3-27c
- Engineering Aid 3 (NAVEDTRA 14069), Nonresident training course, April 1995, Naval Education and Training Command (copy hosted by Navy Tribe), Ch. 9, switches
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 24, 2026. How we research
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