The universal on and off button symbol you see on almost all modern electronics is officially IEC 60417-5009 (a circle broken at the top by a vertical line). However, this is technically a "standby" or "soft power" indicator. A true hardwired "On" is a simple vertical line (IEC 5007), and a true "Off" is an empty circle (IEC 5008). Understanding the exact distinction between these engravings is critical for bench testing, industrial wiring, and preventing parasitic battery drain in DC systems.
The Master On and Off Button Symbol Reference Table
The International Electrotechnical Commission (IEC) maintains the definitive registry for physical hardware markings under the IEC 60417 standard. Below is the complete reference for physical switch and button engravings.
| Symbol Name | IEC 60417 Ref | Visual Description | Binary Origin | Practical Application |
|---|---|---|---|---|
| On (Power) | 5007 | A single vertical line ( | ) | 1 (Closed Circuit) | Hardwired toggle switches, industrial disconnects, heavy machinery. |
| Off (Power) | 5008 | A single circle ( O ) | 0 (Open Circuit) | Hardwired toggle switches, industrial disconnects, heavy machinery. |
| Standby / Soft Power | 5009 | Circle broken at top, line entering ( ⏻ ) | 1 and 0 combined | Consumer electronics, PC power supplies, TVs, microcontroller dev boards. |
| On/Off Toggle (Hard) | 5010 | Circle with line completely through it ( ⏼ ) | 1 inside 0 | Push-button hard power cuts, power strips, battery disconnects. |
How to read this table: The binary origin column explains the physical shape. In early computing and telecommunications, a binary '1' represented a closed circuit (current flowing), and '0' represented an open circuit (current stopped). When the IEEE introduced standard IEEE 1621 in the 1970s to replace the ambiguous English words "On" and "Off" (which caused translation errors on exported machinery), they formalized these binary shapes into the physical engravings we use today.
Regional and Standard Variants: IEC vs. ANSI/NEMA vs. BS
While IEC 60417 dictates what is physically printed on the button, regional electrical codes and engineering bodies dictate how the switch is drawn on a schematic. Never confuse a physical button marking with a schematic symbol.
| Standard Body | Region / Scope | Physical Markings | Schematic Symbols (Paper/CAD) |
|---|---|---|---|
| IEC 60417 | Global (EU, UK, AU, Modern US Electronics) | 5007, 5008, 5009, 5010 engravings on hardware. | Standard IEC switch symbols (e.g., SPST represented by a simple angled line breaking a gap). |
| ANSI / NEMA | United States (Industrial & Commercial) | Adopts IEC for physical consumer goods, but industrial panels may still use text ('START' / 'STOP'). | NEMA schematic symbols (e.g., momentary normally-open contacts drawn with specific limit-switch arrows). |
| BS 3939 (Legacy) | United Kingdom (Pre-1990s) | Largely obsolete. You may find old 'crossed circle' or specific graphic indicators on legacy marine panels. | Superseded by IEC 60617. Old BS symbols used different graphical representations for relays and contacts. |
If you are wiring a control panel in the US, your physical buttons will likely feature IEC 5007/5008 engravings (or green/red color coding per NFPA 79 / ANSI standards), but your CAD drawings must use NEMA/ANSI Y32.2 schematic symbols. Mixing these up during a panel build will cause your wiring to fail inspection.
Rows People Get Wrong (and Faded Marking Protocols)
Even experienced makers and journeymen misinterpret specific rows in the IEC table, leading to phantom loads, bricked microcontrollers, or failed safety inspections.
1. Confusing Standby (5009) with True Off (5008)
The 5009 symbol (the classic "power button" on your PC or TV) does not mean the device is fully disconnected from mains voltage. It indicates a "soft switch." The button triggers a logic gate or a relay that puts the primary power supply into a low-power standby mode.
The Fix: If you are designing a battery-powered ESP32 or Arduino project, never use a 5009-marked switch to cut power to the board. The parasitic draw from the standby circuit will drain a 18650 lithium cell in weeks. Always use a physical SPST toggle switch or a 5010-marked hard disconnect.
2. The 5010 vs. 5009 Visual Trap
Look closely at the difference:
• 5009 (Standby): The vertical line breaks the circle and does not touch the bottom edge.
• 5010 (Hard On/Off): The vertical line goes completely through the circle, touching both the top and bottom edges.
Manufacturers of cheap power strips often lazily mold the 5009 symbol onto a switch that actually performs a hard disconnect, or vice versa. Never trust the molding on unbranded hardware.
On legacy industrial equipment or sun-baked outdoor control panels, the IEC engravings often wear off. If you cannot visually confirm whether a pushbutton is a 5009 (standby) or 5010 (hard disconnect), assume it is 5009 (standby). Do not rely on it for lockout/tagout (LOTO) procedures.
Verification Step: Set your multimeter to continuity mode. Place probes across the load-side terminals of the switch. Press the button to the 'Off' state. If you read < 1 ohm (or hear a beep), the switch is merely routing a logic signal and the main contactor is still closed. You must physically open the upstream breaker to de-energize the circuit.
Frequently Asked Questions
Why does the standard on and off button symbol look like a 1 and 0?
The symbols are a direct visual representation of binary machine code. During World War II, engineers needed a universal way to label toggle switches on radar and sonar equipment that could be understood by Allied forces speaking different languages. A '1' represented a closed circuit (current flowing / On), and a '0' represented an open circuit (current stopped / Off). In 1973, the International Electrotechnical Commission formalized this into IEC 60417, and later, the IEEE 1621 standard specifically mapped these binary shapes to physical power button engravings to eliminate translation errors in global electronics manufacturing.
Is the circle with a line through it an on and off button symbol or just standby?
It depends entirely on whether the line touches the bottom of the circle. If the line breaks the top of the circle and floats in the middle (IEC 5009), it is a standby symbol. It means the button controls a logic circuit that leaves a parasitic draw on the mains. If the line passes completely through the circle and touches both the top and bottom edges (IEC 5010), it is a hard on/off toggle symbol. This indicates a physical mechanical break in the circuit, meaning zero current flows when switched off. Always check the device datasheet (from manufacturers like Schurter or Carling Technologies) to confirm the internal switching mechanism if the engraving is ambiguous.
How do I identify an on and off button symbol on a faded industrial panel?
When physical IEC 5007/5008 engravings are faded, you must identify the switch type by its electrical behavior, not its visual markings. First, de-energize the panel and verify it is dead with a tested voltage meter. Next, use a multimeter in continuity mode across the switch terminals. If the switch is a maintained toggle (stays in the physical On or Off position) and shows infinite resistance (OL) in one position and near-zero resistance in the other, it is functioning as a hardwired IEC 5007/5008 disconnect. If the switch is a momentary pushbutton (springs back when released) and only shows continuity while held down, it is likely triggering a logic relay or contactor coil, functioning as a soft-standby (5009) control. Never assume a faded button provides a safe hard-disconnect for servicing machinery.
