Explanation of Multiple Motor Cable Color Standards

During motor installation, maintenance, and commissioning, cable colors are not just visual differences—they represent a language of safety and standardization. Clear and unified color identification helps technicians quickly determine the function of conductors, reducing the risk of miswiring and electric shock.
Because motor applications involve different national standards and industry practices, it is common to encounter inconsistent cable colors in real projects. Below is a systematic explanation of the meanings and application scenarios of common motor cable color standards.

I. Why Motor Cable Colors Differ

Motor cable colors are not globally unified. The main reasons include:

• Different national or regional electrical standards (IEC, GB, NEC, etc.)

• Industry-specific practices (industrial, power, mining, construction, etc.)

• Differences in equipment age, with old and new standards used in parallel

• Manufacturer internal standards or customer-specific requirements

Therefore, cable color alone should never be the sole basis for identifying circuit functions on site. Terminal markings, drawings, and measurements must always be used for verification.

II. Common Three-Phase Motor Power Cable Color Standards

1. China / IEC Common Practice

In three-phase systems complying with IEC or commonly used domestic industrial standards, the usual color assignments are:

• L1 (U phase): Yellow

• L2 (V phase): Green

• L3 (W phase): Red

• N (Neutral): Light blue

• PE (Protective earth): Yellow-green bi-color

This color scheme is widely seen in domestic factories, motor control cabinets, and packaged equipment.

2. Old National Standards or Traditional Practice

In older equipment or early projects, the following may be encountered:

• Phase A: Yellow

• Phase B: Green

• Phase C: Red

• Neutral: Black

• Earth: Yellow-green bi-color or bare copper

When interfacing new and old systems, special attention must be paid to unified identification.

III. Common International Motor Cable Color References

1. IEC / European Standard (Newer Version)

Under newer IEC standards, three-phase conductors are typically:

• L1: Brown

• L2: Black

• L3: Grey

• N: Blue

• PE: Yellow-green bi-color

This is currently the most common configuration in Europe and many export-oriented machines.

2. North American NEC (USA / Canada)

In North America, color usage is more flexible, but common conventions include:

• Three-phase power: Black / Red / Blue (or Black / Red / Orange)

• Neutral: White or grey

• Ground: Green or bare copper

Since NEC allows multiple combinations, on-site confirmation is especially important.

IV. Motor Internal Lead and Winding Color Identification

1. Stator Winding Lead Colors

Inside motors, winding lead colors are primarily for manufacturer identification and are not governed by a unified national standard. Typical examples include:

• U phase: Red

• V phase: White

• W phase: Blue

The corresponding winding ends may use different colors or numbered sleeves.
Therefore, terminal markings (U1, U2, V1, V2, W1, W2) are more reliable than color when wiring inside a motor.

2. Auxiliary Circuit Colors

Common conventions include:

• Temperature sensors (PT100, thermistors): White or shielded cables

• Brake coils: Black or brown

• Encoders / speed feedback: Multicore color-coded or shielded cables

These circuits are usually clearly identified in drawings or inside the terminal box.

V. Special Importance of the Ground (PE) Conductor Color

Regardless of the standard used, the protective earth (PE) conductor color is almost universally defined as:

• Yellow-green bi-color (must not be used for any other purpose)

In motor installation, the grounding conductor must:

• Be connected independently and reliably

• Never be combined with the neutral conductor

• Use anti-loosening and corrosion-resistant connections

This is a critical circuit for both personal safety and equipment protection.

VI. Practical On-Site Recommendations

• Use color only as an auxiliary reference
  Never rely solely on cable color for wiring decisions.

• Follow drawings and terminal markings
  Always verify motor nameplates, wiring diagrams, and terminal numbers first.

• Re-identify when mixing new and old systems
  Use number sleeves, labels, or heat-shrink tubing to unify identification and avoid confusion during future maintenance.

• Perform electrical verification before commissioning
  Use a multimeter or phase-sequence tester to confirm phases and circuit status.

• Unify standards in export or cross-border projects in advance
  This helps prevent rework and potential safety hazards caused by color differences.

The coexistence of multiple motor cable color standards is a normal reality in industrial environments. Truly safe and reliable practice is not memorizing a specific color, but understanding standard differences, respecting drawings and markings, and confirming through testing. Only in this way can correct wiring, safe operation, and efficient maintenance be ensured in complex engineering projects.