Copper Wire Amp Chart: NEC 310.16 Sizing & Derating Guide

For standard residential branch circuits, 14 AWG copper wire is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps. For larger 240V feeders, 6 AWG copper handles up to 65 amps (commonly used on 60A circuits), and 2 AWG handles 115 amps. These baseline numbers assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway.

How to Read the NEC Copper Wire Amp Chart

The table below is derived directly from Table 310.16 of the National Electrical Code (NFPA 70). It lists the allowable ampacities for insulated copper conductors rated up to 2000 volts.

Quick-Jump to Most Queried Sizes: 14 AWG (15A) | 12 AWG (20A) | 10 AWG (30A) | 8 AWG (40A/50A) | 6 AWG (55A/65A) | 4 AWG (70A/85A) | 2 AWG (95A/115A)

* Note on Small Conductors: Per NEC 240.4(D), the overcurrent protection for 14, 12, and 10 AWG copper is strictly capped at 15A, 20A, and 30A respectively, regardless of the higher values shown in the 75°C and 90°C columns. These asterisked values are primarily used for derating calculations, not for selecting breaker sizes.

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is looking at a spool of THHN wire, seeing it is rated for 90°C, and immediately using the 90°C column to size their breaker. This is a code violation waiting to happen.

To determine which column applies, you must follow the "weakest link" rule outlined in NEC 110.14(C). The ampacity of your circuit is limited by the lowest temperature rating of any connected termination, device, or conductor in the entire run.

• The 60°C Column: Applies to older equipment, non-metallic sheathed cable (NM-B / Romex) regardless of the internal wire's insulation rating, and circuits rated 100A or less where the termination temperature is unmarked.
• The 75°C Column: The modern standard. Most breakers, lugs, and terminal blocks manufactured in the last two decades are rated for 75°C. If you are pulling individual THHN/THWN wires in conduit to a standard modern breaker panel, you will almost always use this column for your final breaker sizing.
• The 90°C Column: Used almost exclusively as the starting point for derating calculations (ambient temperature adjustments and conduit fill bundling). You can use the 90°C ampacity to apply your derating math, but your final adjusted ampacity cannot exceed the 75°C or 60°C limit of your terminations.

Derating Rules and What the Chart Cannot Tell You

Table 310.16 assumes ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When real-world jobsite conditions deviate from this, you must apply derating factors.

How Derating Modifies the Base Value

If you pull multiple circuits through a single conduit, the wires heat each other up. NEC Table 310.15(C)(1) requires you to reduce the base ampacity.

Worked Example: You are pulling four current-carrying 10 AWG THHN conductors through a single EMT conduit to feed a multi-wire branch circuit.
1. Base ampacity from the 90°C column: 40A.
2. Derating factor for 4-6 conductors: 80%.
3. Adjusted ampacity: 40A × 0.80 = 32A.
Because 32A is greater than the 30A limit imposed by NEC 240.4(D) for 10 AWG, you can still safely protect this wire with a 30A breaker. However, if you had 10 conductors in that pipe (derated to 50%), your adjusted ampacity would drop to 20A, forcing you to upsize to 8 AWG wire to maintain a 30A circuit.

What the Table Cannot Tell You

An amp chart is a thermal limit guide, not a comprehensive engineering tool. It will not tell you:

1. Voltage Drop: A 14 AWG wire can safely carry 15A indefinitely without melting, but if you run it 150 feet to a shed, the voltage drop will starve your tools and cause motor burnout. You must calculate voltage drop using the circular mil area found in NEC Chapter 9, Table 8.
2. Physical Lug Fitment: Table 310.16 might tell you that 1/0 AWG is required for a 150A feeder based on your derating math. However, the physical lugs on a standard 150A breaker might only accept up to #2 AWG. You must check the manufacturer's datasheet for termination torque and wire range limits.
3. Short-Circuit Withstand: Ampacity dictates continuous heat dissipation. It does not tell you if the wire will survive the magnetic and thermal forces of a 10,000A short circuit before the breaker trips.

Copper Wire Ampacity FAQ