Stranded Wire Amperage Chart: NEC Table 310.16 Copper Ratings

The ampacity of stranded copper wire depends strictly on its gauge, insulation temperature rating, and installation conditions, as governed by the National Electrical Code (NEC). For standard residential and commercial branch circuits, you will almost always reference the 60°C or 75°C column, while the 90°C column is reserved for derating calculations. The chart below provides the baseline thermal limits before any environmental adjustments are applied.

Stranded Wire Amperage Chart (NEC Table 310.16 Copper)

How to read this table: This data is extracted directly from NFPA 70 (NEC) Table 310.16 for copper conductors. The columns represent the maximum temperature rating of the wire's insulation. Common stranded insulations like THHN and THWN-2 are rated for 90°C in dry locations and 75°C in wet locations. XHHW-2 is similarly rated. Older or specific-use insulations like TW or UF-B are limited to 60°C. The values below assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single raceway.

* Note on small conductors: NEC Section 240.4(D) strictly limits the overcurrent protection for 14, 12, and 10 AWG copper wire to 15A, 20A, and 30A respectively. You cannot use the higher values in the 75°C or 90°C columns to protect these specific gauges with larger breakers, regardless of the insulation rating.

Which Column Applies and How Derating Modifies Base Values

The most common mistake when using a stranded wire amperage chart is defaulting to the 90°C column simply because modern THHN wire is stamped with a 90°C rating. To determine which column legally dictates your final ampacity, you must apply the weakest link rule.

The Weakest Link Rule (Termination Provisions)

NEC 110.14(C) requires that the ampacity of a conductor be selected based on the lowest temperature rating of any connected device, terminal, or splice. Most standard residential and commercial circuit breakers up to 100A are only tested and rated for 75°C terminations. Therefore, even if you pull 90°C THHN stranded wire through your conduit, your baseline ampacity is capped at the 75°C column. If you are connecting to older equipment or specific lighting dimmers rated only for 60°C, you must drop down to the 60°C column.

How Derating Rows Modify the Base Value

If the 75°C column is the legal limit for terminations, why does the 90°C column exist? It serves as your mathematical starting point for ampacity derating. When you bundle more than three current-carrying conductors in a single conduit, or when ambient temperatures exceed 86°F (30°C), the wires cannot dissipate heat effectively. You must reduce the wire's allowable ampacity.

According to NEC Table 310.15(C)(1), if you pull 4 to 6 current-carrying conductors in one conduit, you must apply an 80% derating factor. The code allows you to apply this percentage to the 90°C column value, provided the final derated number does not exceed the 75°C column limit for termination purposes.

In the bundled scenario above, the derated ampacity is 32A. Because 32A is still greater than the 30A baseline required for a 10 AWG circuit, you are legally permitted to use a 30A breaker. However, if you pull 7 to 9 wires, the derated value drops to 28A, forcing you to drop to a 25A or 20A breaker, or upsize the wire to 8 AWG.

What This Chart Cannot Tell You (Voltage Drop & Physical Limits)

An amperage chart only defines the thermal limit of the wire's insulation. It assumes a relatively short run where resistance is negligible. It does not account for voltage drop over distance, nor does it address the physical mechanics of installing stranded wire.

Voltage Drop: The Hidden Ampacity Killer

If you are feeding a 50A subpanel located 150 feet away from your main breaker, 6 AWG stranded copper (rated for 65A at 75°C) appears perfectly adequate on the chart. However, pushing 50A through 150 feet of 6 AWG wire results in unacceptable voltage drop.

Using the standard single-phase voltage drop formula VD = (2 × K × I × L) / CM:

• K (Copper resistance constant) = 12.9 ohms-cmil/ft
• I (Current) = 50A
• L (One-way length) = 150 ft
• CM (Circular mils for 6 AWG) = 26,240

VD = (2 × 12.9 × 50 × 150) / 26,240 = 7.37 Volts

On a 240V circuit, a 7.37V drop is 3.07%—marginally over the 3% recommended limit for feeders outlined in Copper Development Association (CDA) guidelines. But if that subpanel is supplying a 120V branch circuit, the drop represents a massive 6.14%, which will cause lights to dim, motors to overheat, and sensitive electronics to brownout. For a 150-foot, 50A run, you must ignore the thermal chart and upsize to 4 AWG or 2 AWG stranded copper purely to mitigate voltage drop.

Physical Pulling Tension and Bend Radius

Stranded wire is chosen over solid wire for its flexibility, but it is not immune to physical damage during installation. When pulling long runs of large-gauge stranded wire (like 4/0 AWG for a 200A service), you must calculate the maximum pulling tension to avoid stretching the copper strands. Stretching reduces the cross-sectional area, which increases resistance and creates a localized hot spot that the amperage chart cannot predict.

The industry standard maximum pulling tension for copper conductors is 0.008 pounds per circular mil. For 4/0 AWG (211,600 circular mils), the absolute maximum pulling force at the pulling eye is 1,692 pounds. Exceeding this requires upsizing the wire or using a mid-point pull box. Furthermore, you must use a wire-pulling compound (lubricant) rated for the specific insulation type, and strictly observe NEC 300.34 bend radius limits to prevent kinking the stranded bundles inside the conduit.