The Complete Power Symbol Reference Table
Before wiring a panel or debugging a PCB, you must identify exactly which power state a symbol represents. The table below covers the primary IEC 60417 power symbols you will encounter on modern electrical equipment, consumer electronics, and industrial controls.
| Symbol | Official Name | Standard Reference | Circuit State | Practical Application |
|---|---|---|---|---|
| | (Line) | Power On | IEC 60417-5007 | Hard Closed (Energized) | Basic toggles, heavy machinery, hardwired disconnects. |
| O (Circle) | Power Off | IEC 60417-5008 | Hard Open (De-energized) | Basic toggles, emergency stops (when combined with color). |
| ⏻ (Line in broken circle) | Standby / Soft Power | IEC 60417-5009 | Partial Open (Logic Live) | PC power buttons, TVs, modern appliance soft-touch controls. |
| ⏼ (Line in full circle) | On/Off Toggle | IEC 60417-5010 | Alternating State | Single-press pushbuttons that toggle between hard on and hard off. |
Regional and Standard Variants (IEC vs. ANSI vs. Legacy)
While the line and circle symbols are nearly universal today, the surrounding context—such as switch colors and physical orientation—varies by region and governing body.
The Global Baseline: IEC 60417
The International Electrotechnical Commission (IEC) maintains the graphical symbols for use on equipment. If you are working in the EU, UK, Australia, or on modern equipment imported into the US, IEC 60417 is the governing standard. It strictly defines the geometry of the line and circle to ensure language barriers do not compromise safety.
North American Color Codes: ANSI/NEMA vs. OSHA
In the US, the National Electrical Code (NEC) does not dictate the color of the physical switch actuator, but OSHA and ANSI Z535 standards heavily regulate industrial control colors. Under OSHA 1910.145 and ANSI Z535, Green universally indicates START/ON, and Red indicates STOP/OFF.
If you are restoring older US military, aviation, or vintage amateur radio equipment (pre-1980s), you may encounter reversed color coding where Red meant 'Armed/Hot' (ON) and Green meant 'Safe' (OFF). Always verify vintage panels with a multimeter before applying power.
Old UK and Legacy Text Markings
Before the widespread adoption of IEC symbols in the late 1970s, many British and American appliances relied on embossed text ('ON'/'OFF') or simple Roman numerals ('I' and 'O'). While 'I' and 'O' look identical to the modern line and circle, older switches lacked the strict geometric proportions required by modern IEC standards, sometimes leading to confusion in low-light environments.
Rows People Get Wrong and Faded Marking Safety
Even experienced technicians misinterpret specific symbols or make dangerous assumptions when switch markings wear off. Here is how to handle the most common pitfalls.
The 'Standby' Symbol Trap (Row 3)
The most frequently misunderstood row in the reference table is the Standby symbol (⏻). Many users assume this symbol means the device is completely disconnected from mains voltage. It does not. In practice, a standby symbol indicates that the primary high-voltage load is switched off, but a low-voltage secondary circuit remains energized.
For example, in an ATX computer power supply, pressing a standby button cuts the 12V and 5V main rails, but the 5VSB (5V Standby) rail remains live to power the motherboard's wake-on-LAN circuitry and listen for the CMOS power button signal. If you are working inside a chassis marked with the standby symbol, you must physically unplug the IEC C13/C14 power cord to achieve a zero-energy state.
Safe Interpretation When Markings are Faded or Missing
Rocker switches on workshop tools, 3D printers, and bench power supplies frequently lose their painted line and circle markings due to UV exposure and friction. Never guess the switch state based on physical position alone, as internal fulcrum designs vary by manufacturer.
The Multimeter Verification Protocol:
- De-energize: Unplug the device or lock out the breaker. Verify dead with a non-contact voltage tester.
- Set Meter: Switch your multimeter to Continuity mode (the diode/soundwave icon).
- Probe: Place one probe on the line-side terminal and the other on the load-side terminal of the switch.
- Test: Flip the switch. The position that yields a reading of < 1 ohm (and triggers the audible beep) is the | (ON) state. The position that reads 'OL' (Open Loop) is the O (OFF) state.
- Mark: Use a silver paint pen or a piece of colored heat-shrink tubing to permanently re-mark the actuator.
Frequently Asked Questions
Why is the symbol for on and off a line and circle instead of text?
The line and circle symbols were adopted globally to eliminate language barriers in international equipment manufacturing and operation. Following World War II, as electronics and heavy machinery were exported globally, text-based 'ON/OFF' labels proved hazardous for operators who did not read English. The line (representing the binary number 1, or a closed logic gate) and the circle (representing the binary number 0, or an open logic gate) provided a mathematically universal shorthand that transcended spoken language. The IEC formalized this in the 1970s to standardize global switch types and schematics.
Does the line and circle power symbol mean the device is completely disconnected from mains?
Not necessarily. The symbol only tells you the state of the switch mechanism, not the internal wiring topology. Most standard rocker switches are Single-Pole, Single-Throw (SPST), meaning they only break the 'Line' (Hot) conductor. The 'Neutral' conductor remains physically connected to the device's internal circuitry. While the device will not operate, touching internal components can still be lethal if the neutral is floating or if a wiring fault exists. For true, safe isolation (a completely disconnected state), the equipment must use a Double-Pole switch (breaking both Line and Neutral) or be physically unplugged from the receptacle.
Which way does a rocker switch go when the line and circle are oriented vertically?
Under standard IEC and UL design guidelines for vertical rocker switches, pressing the top half inward (depressing the Line / | side) turns the device ON. Pressing the bottom half inward (depressing the Circle / O side) turns the device OFF. This orientation is a deliberate gravity fail-safe: if the internal plastic actuator snaps off or the spring fails, gravity will pull the top of the rocker outward and the bottom inward, defaulting the switch to the safe OFF (O) position rather than leaving a machine unexpectedly energized.
