The universal "On" symbol is a vertical line (| or binary 1), and the "Off" symbol is a circle (O or binary 0). These derive directly from the IEC 60417 standard, representing a closed circuit (continuity) and an open circuit (break), respectively. Below is the definitive reference for identifying, applying, and troubleshooting these markings on the bench and in the field.
The Master On vs Off Symbol Reference Table
This table covers the four primary power state symbols defined by the International Electrotechnical Commission. Use this as your baseline for panel design, schematic review, and equipment labeling.
| Symbol | IEC Designation | Unicode | Circuit State | Practical Meaning & Application |
|---|---|---|---|---|
| | (Line) | IEC 60417-5007 | U+23FD | Closed (Continuity) | Power is fully applied to the load. Used on hard-disconnect rockers, toggle switches, and industrial motor starters. |
| O (Circle) | IEC 60417-5008 | U+23FE | Open (Break) | Power is physically disconnected from the load. The circuit is dead downstream of the switch contacts. |
| ⏻ (Broken Circle w/ Line) | IEC 60417-5009 | U+23FB | Standby (Quiescent) | Low-power state. Main loads are off, but control circuitry, power supplies, or microcontrollers remain energized. |
| ⏼ (Circle w/ Line Through) | IEC 60417-5010 | U+23FC | Push-Push Toggle | Indicates a mechanical latching switch (like a classic TV button) that physically alternates between On and Off states. |
Regional Standards: IEC, IEEE, and Legacy Markings
While the IEC 60417 symbols are globally dominant on physical hardware, regional engineering standards dictate how these concepts are represented in schematics and legacy installations.
IEC 60417 (Global / Consumer / Industrial)
This is the standard printed on 95% of modern hardware, from laptop power bricks to 480V industrial disconnects. If you are designing a PCB for global export or wiring a commercial panel in the EU, Asia, or modern North American facilities, IEC 60417 is your mandatory baseline. The IEC Graphical Symbols Database strictly governs the exact line thickness and proportions of these glyphs to ensure visibility at a distance.
IEEE 315 (US Schematic Standard)
In the United States, electrical schematics often follow IEEE 315 (and its military equivalent, MIL-STD-806). While physical switches on US equipment still use the IEC | and O symbols, the schematic representation differs. IEEE schematics rarely draw the | or O symbols; instead, they use standard SPST/SPDT switch contact symbols (a hinged line breaking a dot) annotated with textual logic states (e.g., 'PB1-NO' for Pushbutton 1 Normally Open). Do not expect to see IEC power glyphs on a US-designed wiring diagram.
Legacy UK / Australian Markings
Older installations in the UK and Australia (pre-1990s) frequently bypassed symbols entirely in favor of text. You will often find "MAINS" (On) and "STANDBY" (Off/Standby), or "I" and "II" on rotary cam switches. If you are retrofitting a legacy control panel, do not assume "II" means off; trace the common and load terminals with a meter to verify the mechanical cam sequence.
The "Rows People Get Wrong" Field Notes
Misinterpreting power symbols leads to energized circuits during maintenance and blown microcontrollers on the bench. Here are the most common errors I see in the field:
The broken circle with a line (⏻) does not mean the device is safe to touch. It indicates a "soft off" state. In a PC power supply or modern appliance, the ⏻ symbol means the high-voltage DC bus or the 5V standby rail is still live. If you are doing internal component-level repair, a switch set to ⏻ will still shock you. You must physically unplug the device or trip the upstream breaker.
Makers often mistake the ⏼ symbol for a "sleep" or "standby" mode. It actually designates a mechanical latching action. If you see ⏼ on a switch datasheet (like a Carling V-series rocker), it means the switch is a push-push alternate-action type. Press it once to latch On (|), press again to latch Off (O). It has no electronic standby logic.
Schematic vs. Physical Mismatch: On a schematic, a switch drawn in the "Off" position (contacts open) might be physically labeled with the "|" symbol on the panel if the panel label indicates the function of the button rather than its current state. Always verify the physical state with a multimeter, never rely solely on the painted panel glyph.
Decision Path: Choosing the Right Switch Symbol for Your Panel
Use this decision tree to select the correct symbol and physical switch type for your next enclosure or PCB design. Follow the logic down to your concrete part selection.
| Your Application Scenario | Required Circuit Behavior | Correct Symbol to Print | Concrete Switch Pick (Part/Type) |
|---|---|---|---|
| Mains Disconnect: Cutting power to a motor, heater, or main distribution board. | Physical air-gap break. Zero current flow. Must meet LOTO (Lockout/Tagout) requirements. | | and O (On/Off) | Eaton or ABB Rotary Isolator Switch (e.g., ABB OT16F3). Hard mechanical detent. |
| Consumer Electronics: TV, monitor, or smart home hub powered by an external brick. | Microcontroller sleep mode. Low quiescent draw, instant wake via IR or network. | ⏻ (Standby) | Tactile momentary switch (e.g., C&K PTS645 series) wired to a GPIO interrupt pin. |
| Battery Tool / Portable: Drill, flashlight, or benchtop 12V tool. | Operator needs to turn it on and walk away without holding the button. | ⏼ (Toggle) | Carling V-Series Contura II rocker switch (maintained/latching SPST). |
| Industrial E-Stop: Emergency halt for CNC or conveyor. | Forces open circuit. Must require a twist or pull to reset. Cannot be accidentally bumped to "On". | O (Often red mushroom head, no "On" symbol printed) | Siemens 3SU1 Emergency Stop push-pull/twist-release (NC contacts). |
Default Recommendation: If you are building a general-purpose DIY enclosure or custom control panel and are unsure which to use, default to the standard | and O printed on a maintained (latching) DPST rocker switch (like the standard SPST/DPST rockers referenced in circuit literature). It provides a hard physical disconnect, is universally understood, and prevents phantom voltage issues.
Safe Interpretation When Markings Are Faded or Missing
In harsh environments—UV exposure, chemical washing, or high-heat industrial ovens—the silk-screened | and O symbols wear off rockers and toggles. Guessing the state of a faded switch is a severe safety hazard.
Before probing any switch with missing markings, de-energize the circuit at the main breaker. Follow OSHA Lockout/Tagout (LOTO) guidelines if working in a commercial facility. Verify the circuit is dead using a known-working non-contact voltage tester or a CAT III/IV multimeter before touching the switch terminals.
Once the circuit is verified dead, use your digital multimeter (DMM) in continuity or resistance mode to map the switch logic:
- Identify the Terminals: A standard SPST rocker has two terminals. A DPST has four (two pairs). A 3-way (ON-OFF-ON) has three terminals per pole (Common, L1, L2).
- Probe for Continuity: Set your DMM to the continuity setting (the diode/sound wave icon). Place one probe on the line feed terminal and the other on the load terminal.
- Map the Positions: Flip the switch to Position A. If the meter reads < 1 ohm (or beeps), Position A is your On (|) state. If the meter reads OL (Over Limit / infinite resistance), Position A is your Off (O) state.
- Permanently Relabel: Do not rely on memory or a sharpie mark that will rub off. Use a Brady or Brother industrial label maker to print high-contrast, adhesive-backed | and O vinyl labels, or use a center punch to create a tactile physical dent next to the "On" position for gloved operators.
By strictly adhering to IEC 60417 definitions and verifying physical continuity rather than trusting faded panel art, you eliminate the most common point of failure in equipment maintenance and custom enclosure wiring.
