Electrician symbols are the standardized shorthand for electrical schematics, governed primarily by ANSI/IEEE 315 in North America and IEC 60617 internationally. If you are reading a blueprint, troubleshooting a motor control center, or tracing a PLC ladder logic circuit, you must instantly recognize whether a circle with a diagonal line means a motor or a generator, and whether a square box represents a contactor or an auxiliary relay. Here is the complete reference to get you oriented on the print.
The Master Electrician Symbols Reference Table
The following table maps the most common control and power components across the two dominant global standards. Use this to cross-reference your physical panel with the schematic in your hand.
| Component | ANSI/NEMA Symbol Description | IEC 60617 Symbol Description | Practical Field Meaning |
|---|---|---|---|
| Circuit Breaker | Square with a manual toggle line and trip curve marker | Rectangle with 'Q' or 'QF' prefix designation | Main overcurrent protection; trips on thermal/magnetic fault. Must be manually reset. |
| Contactor Coil | Circle with 'M' (Motor) or 'CR' (Control Relay) | Rectangle with 'KM' (Contactor) or 'KA' (Aux Relay) | Electromagnetic switch. NEMA uses generic terminal numbers; IEC strictly uses A1/A2 for the coil. |
| Thermal Overload | Heater element symbol (zigzag or box) with 'OL' text | Rectangle with 'F' or 'FR' and a thermal curve line | Protects motor from sustained overcurrent. Trips the control circuit, not the main power line directly. |
| Pushbutton (NO) | Gap with a horizontal line above, labeled 'PB' | Gap with 'S' prefix and '13/14' terminal designations | Normally Open. Closes the circuit only when physically pressed. |
| Pushbutton (NC) | Overlapping lines with an 'X', labeled 'PB' | Overlap with 'S' prefix and '11/12' terminal designations | Normally Closed. Opens the circuit when pressed (common for E-Stop and stop buttons). |
| Transformer | Two overlapping circles (core type) or parallel lines | Two overlapping circles with 'T' prefix and phase dots | Steps voltage up or down. Dots indicate instantaneous polarity (critical for paralleling). |
| Ground / Earth | Three descending horizontal lines (decreasing width) | Three descending lines, or a circle with 'PE' text | Safety earth. 'PE' denotes Protective Earth; 'TE' denotes Technical/Functional Earth (shielding). |
Regional Variants: NEC (NEMA) vs. IEC vs. Old UK
Assuming a single global standard is a fast track to miswiring an imported machine. The physical hardware and the schematic symbols differ significantly based on the region of manufacture.
NEMA (North America)
NEMA (National Electrical Manufacturers Association) symbols are highly abstract and standardized by physical device size (e.g., Size 00 through Size 6). A NEMA schematic focuses on the physical layout of the ladder logic. Power rails are strictly vertical (L1 on the left, L2 on the right), and symbols are drawn exactly as they appear in the physical panel. Coil designations are simple: 'M' for motor starters, 'CR' for control relays.
IEC 60617 (Europe and Global)
IEC symbols prioritize function over physical location. They are modular and rely heavily on alphanumeric cross-referencing. For example, a contactor coil labeled '-KM1' on page 2 of the schematic will control auxiliary contacts also labeled '-KM1' scattered across pages 4, 5, and 6. IEC also mandates specific terminal numbering: coils are always A1/A2, NO contacts are 13/14, and NC contacts are 11/12. This makes tracing circuits on massive 200-page PLC prints vastly easier once you learn the numbering system.
Old UK (BS 3939)
Largely obsolete since the adoption of BS EN 60617 in the late 1990s, you will still encounter BS 3939 symbols in legacy British chemical plants and older marine vessels. It used distinct cross-hatching to denote different phases and a completely different earth symbol (a solid black triangle pointing down). If you are working on a pre-2000 UK facility, request the original BS 3939 legend from the site engineering office before tracing circuits.
The "Rows People Get Wrong" Field Notes
Even experienced journeyman electricians misread specific symbols when fatigued or working under poor lighting. Here are the most common traps and how to avoid them.
- NO vs. NC Contacts: The most frequent error. Remember the visual mnemonic: the 'X' means the contacts are crossed (closed), so current can flow through the X. The gap means the contacts are separated (open). If you wire an E-Stop as NO instead of NC, the machine will fail to stop when the button is pressed.
- Thermal Overload vs. Magnetic Breaker: A thermal overload (heater element) only opens the control circuit (usually terminals 95/96 on IEC blocks) to drop out the contactor coil. It does not physically interrupt the main 480V power line. A circuit breaker symbol indicates it physically interrupts the main power. Confusing the two leads to dangerous assumptions about isolation during LOTO (Lockout/Tagout).
- Faded or Sun-bleached Prints: UV exposure in outdoor control enclosures turns black ink brown, making the 'X' of an NC contact look like a simple overlapping line. Never guess the state of a faded contact based on visual inspection of the paper.
- Transformer Polarity Dots: Ignoring the phase dots on a transformer symbol. If you parallel two control transformers without respecting the dot notation (instantaneous polarity), you will create a dead short across the secondary windings, instantly destroying the transformers and potentially causing an arc flash.
Decision Tree: Identifying Unknown or Faded Symbols
When you are standing in front of a panel with a torn, faded, or poorly translated schematic, do not rely on visual guesswork. Follow this decision path to definitively identify the circuit state.
| Condition / Symptom | Action Step | Expected Result / Concrete Pick |
|---|---|---|
| Print is faded; cannot tell if contact is NO or NC. | 1. Perform LOTO. Verify zero energy. 2. Locate the physical component. 3. Read the terminal block numbers. |
If terminals are 13/14 (IEC) or marked NO, it is Normally Open. If 11/12 or marked NC, it is Normally Closed. |
| Terminal numbers are rubbed off the physical component. | 1. Disconnect the wires from the suspect contact. 2. Set multimeter to Continuity/Ohms. 3. Probe the two terminals. |
Pick: Use a Fluke 87V True-RMS meter. If it beeps (reads < 1.0 Ω), it is an NC contact. If it reads 'OL' (Open Loop), it is an NO contact. |
| Symbol is completely unrecognized (legacy or custom OEM). | 1. Trace the physical wire destination. 2. Identify if it routes to a PLC input card, a neutral bar, or another coil. |
Map the physical wire to the PLC I/O address (e.g., I:0/04) and cross-reference the PLC logic software to determine the symbol's logical function. |
Standard References and Code Compliance
While this guide provides practical field translations, legal and safety compliance always defaults to your local Authority Having Jurisdiction (AHJ). When designing or modifying schematics, ensure your symbol library complies with the governing standard for your region.
In North America, schematic drafting and symbol usage are guided by NFPA 70 (National Electrical Code) for installation rules, and ANSI/IEEE 315 for the actual graphic symbols. NEMA standards (specifically NEMA ICS 1) dictate the physical and schematic representation of industrial control equipment.
For international projects, or when integrating imported machinery, refer to the IEC 60617 database for the definitive, legally binding symbol set recognized across the EU, UK, and most of Asia. Remember that while symbols tell you how a circuit functions, they do not override the physical ampacity, wire sizing, and torque requirements mandated by your local electrical code.
