The two way one gang switch symbol on an electrical schematic represents a Single Pole, Double Throw (SPDT) mechanism. In practical terms, it is a single physical switch rocker (one gang) that allows you to control a single lighting circuit from two separate locations (two way). Before reading any diagram, you must resolve the transatlantic terminology trap: what the UK, Australia, and Europe call a 'two-way' switch, North America calls a '3-way' switch. Conversely, a US '2-way' switch is a standard single-pole (SPST) switch.
Getting this terminology wrong leads to buying the incorrect hardware and misinterpreting schematic symbols. Below is the definitive reference for identifying, interpreting, and wiring this component across global standards.
The Two Way One Gang Switch Symbol Reference Table
This table maps the schematic symbol elements to their physical terminal equivalents on the back of the switch mechanism. Use this to translate paper diagrams to real-world wiring.
| Symbol Element | IEC 60617 (UK/EU/AU) | ANSI/IEEE 315 (US/CA) | Physical Terminal Label | Function in Circuit |
|---|---|---|---|---|
| Common / Pole | Line entering the pivot point | Line entering the hinged arm | COM (or C) | Connects to the permanent live feed OR the switched live drop to the light fixture. |
| Throw 1 / Strapper | Upper diagonal exit line | Upper traveler line | L1 (or T1) | First traveler wire connecting to the matching terminal on the second switch. |
| Throw 2 / Strapper | Lower diagonal exit line | Lower traveler line | L2 (or T2) | Second traveler wire connecting to the matching terminal on the second switch. |
| Gang Indicator | Single switch symbol drawn | Single switch symbol drawn | One physical rocker | Denotes a single control paddle on the faceplate (one gang). |
| Mechanical Link | Dashed line linking gangs (if multi) | Dashed line linking gangs (if multi) | N/A (Internal) | Shows physical linkage; absent on a true one-gang switch. |
Regional Variants: IEC, ANSI, and Legacy Standards
The visual representation of the SPDT symbol changes depending on the drafting standard used by the engineer or electrician who drew your schematic.
- IEC 60617 (International / UK / AU / EU): The symbol typically features a circle at the pivot point with a solid diagonal line representing the moving contact, branching into two distinct dots or short perpendicular lines for L1 and L2. Terminals on the physical switch are stamped COM, L1, and L2. The traveler wires are colloquially called 'strappers'.
- ANSI/IEEE 315 (North America): The symbol shows a break in the main circuit line with a hinged, swinging arm that can bridge to either of two upper/lower contact points. Physical switches (sold as '3-way' switches) typically use a black screw for the Common (C) terminal, and two brass-colored screws for the Travelers (T1, T2). IEEE 315 governs these graphic symbols for electrical diagrams in the US.
- BS 3939 (Legacy UK): Obsolete since the late 1990s but still found in as-built drawings for older properties. It used a more stylized, hand-drawn aesthetic with a distinct 'knife switch' look. The terminal logic remains identical to modern IEC.
Never mix US and UK/AU terminology when ordering parts internationally. If you are in the US and need to control a light from two locations, you must buy a 3-way switch. If you ask for a '2-way switch' in a North American hardware store, they will hand you a standard single-pole switch, which lacks the L1/L2 traveler terminals required for your circuit.
Rows People Get Wrong: Faded Markings and Miswired Terminals
Even experienced DIYers make critical errors when interpreting these symbols and mapping them to physical terminals. Here are the most common failure modes:
- Swapping COM and L1/L2: The schematic shows the permanent live (or switched live drop) going to the Common terminal. If you wire the live feed into L1, the circuit will only work when the switch is in one specific position, and the travelers will remain permanently energized, creating a shock hazard at the second switch.
- Confusing Travelers with Neutral: The symbol shows two parallel lines (L1 and L2) running between switches. Beginners often assume one is a traveler and the other is a neutral. Neither is a neutral. Both travelers carry switched live voltage. The neutral wire bypasses the switches entirely and runs directly to the light fixture.
- The 'One Gang' Jumper Assumption: If you are upgrading to a 2-gang plate where both switches are 2-way, the schematic will show two independent SPDT symbols. However, on many physical UK/AU plates (like standard Crabtree or MK Logic ranges), the two COM terminals are internally isolated. You must install a physical jumper wire between the two COM terminals to share the live feed, a detail rarely shown on simplified schematics.
Decision Path: Selecting the Right Switch and Terminal Mapping
Use this decision tree to select the exact hardware and terminal mapping required for your specific region and application. Do not guess; follow the path to the concrete part number.
| Your Region / Scenario | Standard Required | Concrete Part Recommendation | Terminal Wiring Map |
|---|---|---|---|
| US / Canada (Standard Residential) | ANSI / UL Listed | Leviton Decora 3-Way (5603-W) | Black Screw = COM (Feed or Load) Brass Screws = Travelers Green = Ground |
| UK / AU / NZ (Standard Residential) | IEC / BS EN 60669 | MK Logic Plus 2-Way (K4922WHI) | COM = Permanent Live or Switched Live L1 = Strapper 1 L2 = Strapper 2 |
| Smart Home Upgrade (US - No Neutral at Switch) | ANSI / FCC | Lutron Caseta 3-Way (PD-5S-DV) | Requires Lutron Pico remote at the second location. Main switch wires to Line, Load, and Ground. Travelers are capped off. |
| Smart Home Upgrade (UK/EU - 2-Wire Lighting) | IEC / CE / UKCA | Shelly Plus 1PM (at the light fixture) | Keep existing mechanical 2-way switches. Wire Shelly at the ceiling rose. Switches act as signal inputs (SW1/SW2) to toggle the relay. |
Safe Verification When Markings Are Missing
If you are troubleshooting an existing installation where the physical terminal stamps (COM, L1, L2) are faded, painted over, or missing, do not guess based on screw position. Manufacturers change terminal layouts between production runs. You must electrically verify the Common terminal using a digital multimeter.
- Isolate and Remove: Turn off the breaker, verify dead, and remove the switch from the wall. Disconnect all wires from the back of the switch.
- Set Multimeter to Continuity: Set your multimeter to the continuity/diode test mode (the setting that beeps when probes touch).
- Find the Common (COM): Place one probe on Terminal A and the other on Terminal B. Toggle the switch. If it beeps in one position but not the other, move the second probe to Terminal C. If it now beeps in the opposite toggle position, Terminal A is your Common (COM).
- Verify the Travelers: The Common terminal will show continuity to either Terminal B or Terminal C depending on the rocker position. Terminals B and C will never show continuity to each other. These are your L1 and L2 travelers.
- Tag and Reconnect: Wrap a piece of red electrical tape around the wire that belongs on the COM terminal (usually the permanent live feed or the drop to the light) to ensure it goes back to the verified Common terminal.
For further reading on safe isolation procedures and standard wiring colors, consult the guidance provided by Electrical Safety First (UK) or your local Authority Having Jurisdiction (AHJ). Always remember that while schematic symbols are universal within their standard, the physical execution must strictly adhere to local electrical codes.
