# ANSI three-way switch plan symbol

Canonical URL: https://eloragrid.ai/symbols/ansi-three-way-switch
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: S3
Drawing use: GA
Reference families: IEEE / ANSI

## Symbol convention

Convention: IEEE / ANSI
Form: 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.

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.

### Terms

- 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.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/)


## 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.

## Important distinction

S4 is a four-way intermediate device; S3 is the changeover switch used at the ends.

## Facts

- Contact: Single changeover, three terminals
- IEC equivalent term: Two-way switch
- Artwork scope: Original educational illustration; the exact ANSI or IEEE graphic and compliance are not certified

## Public references

- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. Graphic-symbol standards context; not a source of reproduced artwork.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.