When electricians and engineers search for a 'circuit 3 phase wire color chart up to # 100', they are almost always looking for the standard color codes and American Wire Gauge (AWG) sizing for a 100-amp 3-phase circuit. (There is no #100 AWG power wire; 1/0 AWG is roughly 150A, and 3 AWG is exactly 100A). For a standard US 208Y/120V 3-phase circuit up to 100 amps, the NEC mandates Black (Phase A), Red (Phase B), and Blue (Phase C). For 480Y/277V systems, the colors shift to Brown, Orange, and Yellow. The minimum wire size for a non-continuous 100A load is 3 AWG Copper in the 75°C column, but if the load is continuous (3 hours or more), you must upsize to 1 AWG or 1/0 AWG to satisfy the 125% continuous load rule.
The NEC 3-Phase Wire Color & Sizing Chart (Up to 100A)
The table below maps standard 3-phase breaker sizes to their required copper wire gauges and mandated insulation colors. This chart assumes standard 3-phase, 4-wire (plus ground) wye configurations.
| Breaker Size | Cu Wire Size (75°C) | 208V Colors (A, B, C) | 480V Colors (A, B, C) | Neutral | Equipment Ground |
|---|---|---|---|---|---|
| 15A | 14 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 20A | 12 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 30A | 10 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 40A | 8 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 50A | 8 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 60A | 6 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 70A | 4 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 80A | 4 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 90A | 3 AWG | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
| 100A | 3 AWG (or 1 AWG)* | Black, Red, Blue | Brown, Orange, Yellow | White / Gray | Green / Bare |
How to Read This Chart: Columns, Temperature, and Derating
A wire color chart is only half the battle; picking the right column for your ampacity is where most DIYers and junior techs fail. Here is how to interpret the data above.
Which Column Applies to Your Installation?
The wire sizes listed above use the 75°C column of NEC Table 310.16. Why? Because while modern THHN wire is rated for 90°C, the termination lugs on almost all standard breakers, panelboards, and disconnects rated 100A or less are only tested and listed for 75°C (per NEC 110.14(C)). You must size the wire based on the weakest link in the chain, which is the terminal lug. Always use the 75°C column for final sizing.
How Derating Rows Modify the Base Value
The chart above assumes you have three current-carrying conductors in a raceway. But a 3-phase, 4-wire wye system pulling a neutral means you have four current-carrying conductors in the conduit. According to NEC 310.15(C)(1), 4 to 6 current-carrying conductors require an 80% derating factor.
Here is where the 90°C column saves you. You cannot use the 90°C column for final termination sizing, but you can use it for derating math:
- 3 AWG THHN (90°C column): 115 Amps × 0.80 derating = 92 Amps. (This fails a 100A breaker).
- 2 AWG THHN (90°C column): 130 Amps × 0.80 derating = 104 Amps. (This passes).
The Takeaway: If you are pulling a neutral in the same conduit as your three 100A phase wires, you must step up to 2 AWG Copper to survive the derating penalty, even though the breaker lugs are 75°C rated.
Quick-Jump Reference: Most Queried 3-Phase Sizes
Bookmark this section for the three most common 3-phase commercial and heavy-residential feeder sizes.
Wire: 10 AWG Copper. Colors: Black, Red, Blue. Ground: 10 AWG Green. No neutral required for pure 3-phase motors.
Wire: 6 AWG Copper. Colors: Black, Red, Blue. Neutral: 6 AWG White (if 120V loads exist). Ground: 8 AWG Green/Bare.
Wire: 3 AWG Copper (non-continuous) or 1 AWG (continuous). Colors: Black, Red, Blue. Neutral: 3 AWG or 1 AWG White. Ground: 8 AWG Green.
Decision Tree: Picking Your Exact Wire and Color for 100A
Use this decision path to terminate your 100-amp 3-phase circuit selection. Follow the logic down to your concrete pick.
| Condition | Decision / Action |
|---|---|
| Is the system 208Y/120V? | Use Black (A), Red (B), Blue (C). Proceed to load type. |
| Is the system 480Y/277V? | Use Brown (A), Orange (B), Yellow (C). Proceed to load type. |
| Is it a 240V High-Leg Delta? | Use Black (A), Orange (B - High Leg), Blue (C). The wild leg must be Orange per NEC 230.56. |
| Is the 100A load continuous (3+ hrs)? | Multiply 100A × 1.25 = 125A. Select 1 AWG Copper. |
| Is the load non-continuous? | Select 3 AWG Copper. |
| Are you pulling a neutral in the same conduit? | Apply 80% derating. Step up to 2 AWG Copper minimum. |
| Is the run over 100 feet? | Calculate voltage drop. Typically requires stepping up one more AWG size (e.g., to 1/0 AWG). |
What This Table Cannot Tell You (And When to Call an Engineer)
While this chart covers 95% of standard 3-phase installations up to 100 amps, reference tables have hard limits. Here is what the data above cannot account for:
- Voltage Drop Over Distance: NEC Table 310.16 dictates ampacity (heat dissipation), not voltage drop. If your 100A panel is 250 feet from the transformer, 3 AWG wire will experience severe voltage drop, potentially damaging 3-phase motors. For runs over 100 feet, use a voltage drop calculator and expect to upsize to 1/0 AWG or 2/0 AWG. The NEC recommends a maximum 3% drop for feeders (OSHA and NEC informational notes provide further guidance on power quality).
- High-Leg Delta Nuances: If you are working on an older 240V Delta system, Phase B (the high leg) will measure 208V to ground instead of 120V. The chart above assumes standard Wye systems. Never land the Orange high-leg on a standard 120V breaker or neutral bus; it will cause an immediate, violent fault.
- Ambient Temperature Corrections: The 75°C and 90°C columns assume an ambient temperature of 30°C (86°F). If your conduit runs across a roof or through a boiler room where ambient temps exceed 86°F, you must apply the temperature correction factors in NEC Table 310.15(B)(1), which will further reduce your wire's ampacity.
- Local AHJ Amendments: Some municipalities ban specific wire types (like NM-B inside commercial drop ceilings) or require aluminum wire for feeders over 60A to prevent copper theft. Always verify with your local Authority Having Jurisdiction (AHJ) before pulling wire.
By defaulting to 2 AWG Copper THHN for a 100A 3-phase, 4-wire circuit, you build in a safety margin that satisfies termination ratings, conduit derating, and minor voltage drop over standard commercial distances. Always verify dead with a tested multimeter before terminating, and torque all lugs to the manufacturer's exact inch-pound specifications.
