Power Symbol Electrical Reference: IEC Codes, Schematics, and Pinouts

The universal electrical power symbols on physical switches are defined by the IEC 60417 standard: a vertical line (|) means Power On, a circle (O) means Power Off, and a circle broken by a line (⏻) indicates Standby or soft-power. In circuit schematics, DC power is represented by long and short parallel lines, while AC power is denoted by a sine wave inside a circle. This guide provides the exact standard references, schematic variants, and a decision path for interpreting or specifying these symbols in your next build.

The Master Power Symbol Reference Table

The following table covers both physical switch markings (IEC 60417) and schematic source symbols (IEEE/IEC). Use this as your bench-side cheat sheet.

Symbol / Graphic	Standard Ref	Name	Meaning in Practice
| (Vertical Line)	IEC 60417-5008	Power On	Hard connection to mains or primary DC rail. Circuit is fully energized.
O (Circle)	IEC 60417-5009	Power Off	Physical disconnection of the circuit. Zero current flow (excluding leakage).
⏻ (Circle + Line)	IEC 60417-5010	Standby / Soft Power	Primary load is off, but auxiliary logic (e.g., 5VSB) remains energized to listen for a wake signal.
—| |— (Long/Short Lines)	IEEE 315 / IEC 60617	DC Voltage Source	Long line is always positive (+), short line is negative (-). Indicates a battery or DC supply.
~ (Sine Wave in Circle)	IEEE 315 / IEC 60617	AC Voltage Source	Alternating current source. Nominal voltage (e.g., 120V RMS) is usually written adjacent to the symbol.
⏚ (Three descending lines)	IEEE 315	Earth Ground	Physical connection to earth via a grounding rod. Used for safety and fault current clearing.

Regional Standards and Schematic Variants

While physical switch symbols (the |, O, and ⏻) are globally harmonized under IEC 60417, schematic symbols for power and ground split depending on your region and the governing standard body.

US (IEEE / MIL-STD) vs. Global (IEC)

If you are designing schematics for a US-based firm or adhering to IEEE 315, you will use the traditional ground symbols: Earth (three descending horizontal lines), Chassis (three diagonal lines branching from a horizontal bus), and Signal/Common (an empty or filled triangle).

In the EU and regions strictly following IEC 60617, ground symbols are often simplified to a single line with three downward branches, or a simple downward-pointing arrow for signal ground. Assumption for this guide: We default to IEEE 315 for schematic symbols as it remains the dominant standard in North American EDA tools like Altium and KiCad, while defaulting to IEC 60417 for physical hardware silkscreen and switch markings.

Rows People Get Wrong (and How to Fix Them)

Misinterpreting a power symbol on the bench can lead to bricked microcontrollers or shocked fingers. Here are the most common errors.

• DC Source Polarity Reversal: Hobbyists frequently draw the short line as positive because it looks like the 'plus' sign's vertical bar. Correction: The long line represents the larger physical plate of a voltaic cell, which is historically and universally the positive terminal.
• Earth vs. Chassis Ground: Connecting a noisy motor return to Earth Ground instead of Chassis Ground will inject EMI directly into your safety ground path, potentially causing GFCI nuisance trips. Correction: Use Chassis ground for shielding and motor returns; reserve Earth ground strictly for fault clearing and safety bonding.
• Faded Rocker Switches: Assuming the top of a DPST rocker switch is always 'On'. Correction: Switch orientation depends on the panel cutout and internal pivot. Never trust the physical orientation without a continuity test.

Decision Tree: Which Power Symbol to Specify

Use this decision path to select the exact symbol for your PCB silkscreen, front panel design, or schematic documentation.

If your application is...	Then specify...	Concrete Pick / Standard
A hard-switched mains device (e.g., bench power supply, lamp)	Line and Circle symbols side-by-side or on a rocker	IEC 60417-5008 & 5009
A microcontroller-driven soft-latch power button	The broken circle symbol	IEC 60417-5010 (⏻)
Drawing a schematic for a US-manufactured product	IEEE standard ground symbols (Earth, Chassis, Signal)	IEEE 315 / ANSI Y32.2
Indicating a primary AC mains input on a block diagram	Sine wave inside a circle with RMS voltage noted	IEC 60617-S15

Safe Interpretation When Markings are Faded or Missing

On older industrial equipment or cheap imported power strips, the | and O markings often wear off, or the switch is an unmarked DPDT (Double Pole, Double Throw) toggle. Here is the exact procedure to safely map the pinout.

1. De-energize and Isolate: Unplug the device from mains voltage. If hardwired, turn off the branch breaker, apply a lockout/tagout (LOTO) device, and verify zero voltage at the terminals with a known-working CAT III multimeter.
2. Set DMM to Continuity: Switch your multimeter to the continuity/diode test mode (the setting that beeps when probes touch).
3. Map the Pivot: For a standard 4-pin rocker switch (DPST), the two pins on one side are the Line/Load pairs, and the two on the other side are the mating pairs. Place one probe on Pin 1 and the other on Pin 3.
4. Toggle and Test: Flip the switch. If the meter beeps, that physical direction is your | (Power On / IEC 60417-5008). If it reads 'OL' (Open Loop), that direction is your O (Power Off / IEC 60417-5009).
5. Label Permanently: Use a paint pen or engrave the panel with the correct IEC symbol. Do not rely on tape or marker, which will degrade in high-heat environments like amplifier racks or motor control centers.

By strictly adhering to IEC 60417 for physical interfaces and IEEE 315 for schematic documentation, you eliminate ambiguity. When in doubt, default to the hard-disconnect (| / O) symbols for any circuit carrying over 50V AC or 120V DC, as local electrical codes (such as the NEC) frequently mandate a visible, physical disconnecting means for safety compliance.