The standard 3 phase electrical symbol on schematics is a sine wave paired with the number three and a tilde (3~), while physical conductor identification relies on strict regional color codes. Whether you are reading a schematic or terminating a VFD, misinterpreting these markers can lead to catastrophic equipment failure. Below is the complete reference for schematic symbols and physical wire colors.
3 Phase Electrical Symbol & Schematic Reference
On single-line diagrams and schematics, 3-phase components are represented by specific geometric markers and IEC 81346 designator letters. The universal marker for a 3-phase AC source or connection is the 3~ symbol (indicating three alternating current phases).
| Component | Schematic Symbol Description | Standard Designator | Terminal Markings |
|---|---|---|---|
| 3-Phase Source / Bus | Three parallel horizontal lines with '3~' above, or three overlapping sine waves. | L1, L2, L3 | R, S, T (Legacy) or U, V, W |
| 3-Phase Motor | Circle containing 'M' and '3~'. Three lines exiting the circle representing stator windings. | -M | U, V, W (IEC) or T1, T2, T3 (NEMA) |
| 3-Phase Transformer | Two sets of three overlapping coils (primary/secondary). Often includes vector group text (e.g., Dyn11). | -T | 1U, 1V, 1W / 2U, 2V, 2W |
| 3-Phase Circuit Breaker | Three parallel lines interrupted by a switch symbol, tied together by a horizontal mechanical linkage bar. | -Q or -CB | Line (In) / Load (Out) |
| 3-Phase Receptacle | Circle with 3 angled inner lines (phases) and 1 straight line (ground/neutral). | -X or -P | L1, L2, L3, PE, N |
3-Phase Wire Color Codes by Region
Physical wire colors dictate phase rotation and safety grounding. The colors change drastically depending on whether you are working under North American NEC standards, European IEC 60446 standards, or legacy UK wiring. Always verify the local standard before assuming a wire's function based on its jacket color.
| Conductor | US / Canada (NEC 2020+) | EU / IEC 60446 | Old UK (Pre-2004) |
|---|---|---|---|
| Phase 1 (L1) | Black | Brown | Red |
| Phase 2 (L2) | Red (Orange for High-Leg) | Black | Yellow |
| Phase 3 (L3) | Blue | Grey | Blue |
| Neutral (N) | White or Grey | Blue | Black |
| Protective Earth (PE) | Green, Green/Yellow, or Bare | Green/Yellow | Green/Yellow |
For deeper reading on international harmonization of these colors, the IET Wiring Regulations provide the historical context for why the UK shifted from red/yellow/blue to brown/black/grey to align with mainland Europe.
Rows People Get Wrong (And How to Fix Them)
The High-Leg Delta (Wild Leg) Trap
In North America, a 240V 3-phase delta system with a center-tapped neutral is common in older manufacturing. L1 and L3 will yield 120V to neutral. However, L2 (the 'high leg' or 'wild leg') yields 208V to neutral. If you mistakenly wire a standard 120V control circuit to the red L2 wire instead of the mandated orange wire, you will instantly destroy the 120V load. NEC Article 110.15 requires this high-leg to be durably marked, usually with orange tape or an orange jacket.
Faded Wires and Phase Rotation
When colors are faded or missing, junior technicians often guess the phase rotation. Guessing wrong will run 3-phase motors in reverse, potentially destroying pumps or compressors. To safely interpret missing markings:
- Set your multimeter to AC Voltage (V~), minimum CAT III 600V rating.
- Measure phase-to-phase (L1-L2, L2-L3, L1-L3). You should read a balanced ~208V, ~400V, or ~480V across all three pairs.
- Measure phase-to-ground. In a Wye system, all three will read line-to-neutral voltage (e.g., 277V on a 480V system). In a corner-grounded Delta, one phase will read 0V to ground.
- Use a dedicated phase rotation meter (like the Fluke 87V with phase rotation add-on or a dedicated Fluke 9040) to confirm L1-L2-L3 sequence before energizing the motor.
For a comprehensive breakdown of testing procedures, Fluke's guide on 3-phase power details the exact voltage matrices you should expect on healthy systems.
3 Phase Electrical Symbol FAQ
What does the 3 phase electrical symbol look like on a motor nameplate?
On a physical motor nameplate, the 3 phase electrical symbol is rarely just '3~'. Instead, you will see a wiring diagram showing either a Wye (Star) symbol (three lines meeting at a central point, resembling a 'Y') or a Delta symbol (a triangle). The nameplate will map these symbols to the physical terminal block pins. If you are wiring an IEC motor, look for terminals marked U1, V1, W1 and U2, V2, W2. If you are wiring a NEMA motor, the terminals will be marked T1 through T9. Confusing IEC and NEMA pinouts when wiring a Variable Frequency Drive (VFD) is a leading cause of blown drive IGBTs.
How do I identify 3 phase wires when the insulation colors are faded or painted over?
When visual identification fails, you must build a voltage matrix. Using a properly rated digital multimeter, measure the voltage between every possible wire pair and between each wire and the ground bus. Record the results in a grid. The three wires that show full line-to-line voltage (e.g., 480V) between each other, and equal line-to-neutral voltage (e.g., 277V) to ground, are your three phases. The wire showing 0V to ground but 277V to the phases is your neutral. The wire showing 0V to everything is your ground. Once identified, immediately apply color-coded heat shrink or phase tape (Brown, Black, Grey for IEC; Black, Red, Blue for NEC) to the ends of the wires.
What is the schematic symbol for a 3 phase circuit breaker?
The schematic symbol for a 3-phase breaker consists of three parallel lines, each interrupted by a diagonal or hinged switch blade. Crucially, a horizontal dashed or solid line connects all three switch blades. This horizontal line represents the mechanical tie bar. It indicates that if an overcurrent event or short circuit occurs on any single phase, the mechanical linkage forces all three poles to trip simultaneously, completely isolating the 3-phase load. If you see three parallel switches without this horizontal tie line, it represents three separate single-pole breakers, which is a dangerous and code-violating way to protect a 3-phase motor.
