The "on off symbols circle line" system is rooted in binary logic and globally standardized under IEC 60417. A vertical line (|) represents binary 1 (ON / circuit closed), a circle (O) represents binary 0 (OFF / circuit open), and a circle intersected by a line (⏻) indicates a soft-power or standby state. When designing control panels, wiring appliances, or debugging custom PCBs, misinterpreting these symbols can lead to working on energized circuits when you expect a hard disconnect.
The Complete On Off Symbols Reference Table
Use this spec-sheet table to identify the exact symbol, its binary origin, and its physical application in electrical design. This table covers the primary IEC 60417 identifiers you will encounter on bezels, silkscreens, and schematics.
| Symbol | Name | Binary Origin | IEC 60417 ID | Practical Meaning | Typical Application |
|---|---|---|---|---|---|
| | | Line | 1 (True) | 5007 | ON: Power is applied, circuit is closed. | Mains rocker switches, toggle switches, heavy machinery. |
| O | Circle | 0 (False) | 5008 | OFF: Power is removed, circuit is open. | Mains rocker switches, toggle switches, heavy machinery. |
| ⏻ | Power / Standby | N/A | 5009 | Soft Power: Device is in standby; logic is active but main loads are off. | Consumer electronics, PC motherboards, custom PCBs. |
| ⏼ | Power On/Off | N/A | 5010 | Hard Power: Completely disconnects the device from the power source. | Desktop PC PSU rear switches, industrial control cabinets. |
| ▷ | Play / Run | N/A | 5538 | Start: Initiates motor run or process cycle. | Motor starters, VFD keypads, conveyor controls. |
Regional Standards and Interpreting Faded Markings
While the IEC 60417 symbols are universally recognized on consumer electronics and PCB silkscreens, the physical switches and pushbuttons that carry these symbols are governed by regional industrial standards. If you are wiring a control panel, the symbol is only half the battle; the color of the actuator matters just as much.
IEC 60204-1 vs. NFPA 79: In the EU and globally, IEC 60204-1 dictates that a START (ON) pushbutton must be Green, White, or Grey, while a STOP (OFF) pushbutton must be Red. In the US, NFPA 79 (the Electrical Standard for Industrial Machinery) largely harmonizes with this, but you will frequently encounter legacy US panels where Red is used for START (indicating "danger/motion") and Green for STOP. Always verify the panel's specific schematic rather than relying solely on button color in older US installations.
Safe Interpretation When Markings are Faded or Missing
On older machinery or heavily used bench equipment, the painted O and | symbols often wear off. Never guess the switch state based on the physical toggle position (up/down or left/right), as internal wiring may have been modified.
- De-energize the panel if possible, or use a Non-Contact Voltage Tester (NCVT) to verify the enclosure is safe to open.
- Set your multimeter to Continuity (the diode/sound icon).
- Probe the switch terminals. If you read less than 1 ohm across the line and load terminals, the circuit is closed (ON), regardless of the toggle position.
- Check for failed internals: If the switch is physically in the suspected "O" (OFF) position but you still read continuity, the internal contacts have welded together. The switch must be replaced immediately; it is a severe fire hazard.
Rows People Get Wrong: Common Symbol Confusions
Even experienced makers and electricians trip up on the nuances between the standby and hard-disconnect symbols. Here are the most common misinterpretations:
- The Standby Trap (⏻): The IEC 5009 standby symbol does not mean the device is safe to work on. In a standard ATX computer power supply or a modern TV, pressing the ⏻ button leaves the primary side of the Switch Mode Power Supply (SMPS) fully energized at mains voltage. The 5V standby rail remains live to listen for the "wake" signal. Treat any device showing only a ⏻ symbol as electrically live until unplugged.
- Circle with Line Inside (⏼) vs. Broken Circle (⏻): The ⏼ symbol (IEC 5010) features a line inside an unbroken circle. This designates a hard power toggle that physically breaks the mains connection (like the switch on the back of a PC power supply). The ⏻ symbol features a line breaking the top of the circle, designating a logic-level soft switch.
- Momentary vs. Latching Schematics: On a schematic, a switch symbol with a dashed line connecting multiple poles indicates a mechanically linked latching switch. A switch symbol with a curved line and an arrow pointing away indicates a momentary pushbutton (returns to off when released). Do not confuse the physical bezel icon (| or O) with the schematic switching action.
Decision Path: Selecting the Right Switch and Symbol
Use this decision tree to terminate your design process with a concrete component pick. Do not mix soft-power logic switches with hard mains disconnects.
| Application Scenario | Required Symbol | Switch Action | Concrete Part Pick |
|---|---|---|---|
| Hard mains disconnect for a 120V/240V appliance or custom enclosure. | | / O (IEC 5007/5008) | Maintained (Latching) DPST | Carling V-Series DPST Rocker (Rated 20A 125VAC, features integrated neon indicator). |
| Logic-level soft start / sleep wake for an ESP32 or Arduino custom PCB. | ⏻ (IEC 5009) | Momentary (Normally Open) | C&K PTS645 Series 12mm tactile switch (Use with an ESP32 deep-wake GPIO interrupt). |
| Total hard kill switch for a desktop PC or server rack PDU. | ⏼ (IEC 5010) | Maintained DPST or 3PST | Schurter 48x48 Series rocker with IP65 bezel protection. |
| Industrial motor start/stop station on a factory floor. | ▷ / O (Run/Stop) | Momentary NO (Start) / NC (Stop) | Eaton FAZ-R or Siemens 3SU1 22mm flush pushbutton series. |
Wiring the Physical Switches Behind the Icons
When you select a physical rocker switch bearing the | and O symbols, wiring the integrated indicator LED correctly is crucial for safety and user feedback. The most common mistake is wiring the LED in parallel with the load without a current-limiting resistor, or wiring it so the LED illuminates when the switch is in the O (OFF) position.
Mains Voltage Warning: The following wiring procedure involves 120V/240V AC mains. De-energize the circuit at the breaker, lock out the panel, and verify dead with a tested CAT III or CAT IV multimeter before touching any terminals. If you are not comfortable with mains wiring, hire a licensed electrician.
Correct SPST Rocker Wiring (with Neon/LED Indicator):
- Identify the Terminals: A standard illuminated rocker has three terminals. Terminal 1 is Line (Mains Hot input). Terminal 2 is Load (Output to your device). Terminal 3 is Neutral (or the second Hot leg in a 240V split-phase setup) to complete the indicator circuit.
- Connect the Mains Hot: Wire your black (or brown) mains hot wire to Terminal 1.
- Connect the Load: Wire the black (or brown) load wire going to your device to Terminal 2.
- Connect the Indicator Return: Wire the white (or blue) neutral wire to Terminal 3.
When the rocker is pressed to the | (ON) position, internal contacts bridge Terminal 1 to Terminal 2 (powering the load) AND Terminal 1 to Terminal 3 (powering the internal LED). When pressed to O (OFF), both circuits open simultaneously. If your LED lights up when the switch is in the O position, you have swapped Terminal 1 and Terminal 2. While the device will still function, this creates a confusing user interface and violates standard electrical design practices.
