S2W
Two-way light switch plan mark
Plan mark for a two-way switch used in pairs so one lighting group can be switched from two places.
IEC
IEEE / ANSI · S3
ANSI three-way switch plan symbol
US plan symbol S3 for a three-way switch, used in pairs to control lights from two locations.
In plain English
What does ANSI three-way switch plan mean?
The US three-way switch is drawn as S with subscript 3. Two S3 symbols appear on the plan at different entries, connected by switch legs to the same lighting group, and the installer runs travellers between them.
A simple example
Despite the name, a three-way switch has a single changeover contact. The name refers to its three terminals. The equivalent IEC term is a two-way switch. The symbol does not show traveller routing or box fill; the installer plans this from the pair.
What the drawings help you do
Expect S3 symbols in pairs. Look for S4 symbols between them on long runs. S4 is a four-way intermediate device; S3 is the changeover switch used at the ends.
This particular reference
US plan symbol S3 for a three-way switch, used in pairs to control lights from two locations. S4 is a four-way intermediate device; S3 is the changeover switch used at the ends.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
- Terminal
- An identified point where a conductor connects.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
IEEE / ANSI · Three-way switch, S3
US architectural electrical plan practice in the ANSI Y32.9 lineage, read alongside IEEE 315 context; independently drawn, not a certified IEEE or ANSI graphic.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
GA · S3
What it represents
The US three-way switch is drawn as S with subscript 3. Two S3 symbols appear on the plan at different entries, connected by switch legs to the same lighting group, and the installer runs travellers between them.
Despite the name, a three-way switch has a single changeover contact. The name refers to its three terminals. The equivalent IEC term is a two-way switch. The symbol does not show traveller routing or box fill; the installer plans this from the pair.
How to read it
- Expect S3 symbols in pairs.
- Look for S4 symbols between them on long runs.
Information to show or reference
- Show both S3 locations.
- Link to the same fixtures.
- Allow for travellers in conduit fill.
A distinction that matters
S4 is a four-way intermediate device; S3 is the changeover switch used at the ends.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
Graphic-symbol standards context; not a source of reproduced artwork.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
Explore related references
S4
ANSI four-way switch plan symbol
US plan symbol S4 for a four-way switch placed between two three-way switches to add control points.
IEEE / ANSI
S
ANSI single-pole switch plan symbol
US-style plan symbol for a single-pole wall switch: the letter S at the switch position with a switch leg to the lights.
IEEE / ANSI
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