How to Read the NEC Cable Amps Rating Chart

For standard residential and commercial branch circuits using copper wire, the direct answer for sizing relies on NEC Table 310.16. However, picking the right number isn't just about matching the breaker size to the ampacity column. You must select the correct temperature column based on your circuit's amperage and the equipment's terminal ratings.

Here is the golden rule for which column applies to your installation per NFPA 70 (NEC) 110.14(C)(1):

  • Use the 60°C column for circuits rated 100A or less, or for wire sizes 14 AWG through 1 AWG. This applies even if your wire insulation is rated for 90°C (like THHN), because standard residential breakers and receptacles are rarely tested or listed for higher temperature terminations at these sizes.
  • Use the 75°C column for circuits rated over 100A, or for wire sizes larger than 1 AWG. Most commercial panels and subpanel lugs are rated for 75°C terminations.
  • Use the 90°C column strictly as your starting base for derating calculations (adjusting for high ambient heat or bundling multiple wires in a conduit). You almost never use the 90°C column for final breaker sizing.
Bench Tip: If you are running NM-B (Romex) cable, the ampacity is permanently capped at the 60°C column regardless of wire size, because the overall cable jacket assembly is only rated to 60°C.

The Master Copper Cable Amps Rating Chart (NEC Table 310.16)

The following table provides the allowable ampacities for insulated copper conductors rated up to 2000 volts, assuming an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway or cable. Data is sourced directly from the Copper Development Association and NEC Table 310.16.

AWG / kcmil 60°C (140°F)
TW, UF, NM-B		 75°C (167°F)
THW, THWN, XHHW		 90°C (194°F)
THHN, THWN-2
14152025
12202530
10303540
8405055
6556575
4708595
385100110
295115130
1110130145
1/0125150170
2/0145175195
3/0165200225
4/0195230260

Quick-Jump: Most Queried Wire Sizes & Breaker Pairs

Bookmark this section for the most common residential and light-commercial branch circuits. These assume copper wire, standard 30°C ambient conditions, and standard equipment terminations.

  • 15A Breaker: 14 AWG Copper (60°C column = 15A). Minimum for general lighting.
  • 20A Breaker: 12 AWG Copper (60°C column = 20A). Standard for kitchen/bath receptacles.
  • 30A Breaker: 10 AWG Copper (60°C column = 30A). Standard for dryers and RV outlets.
  • 40A Breaker: 8 AWG Copper (60°C column = 40A). Standard for electric ranges and EV Level 2 chargers.
  • 50A Breaker: 6 AWG Copper. Edge case: The 60°C column lists 6 AWG at 55A. Per NEC 240.4(B) (the 'next size up' rule), because 55A does not correspond to a standard breaker size, you are legally permitted to use the next standard breaker size, which is 60A. However, for a strict 50A load, 6 AWG is the correct physical wire.
  • 100A Subpanel Feeder: 3 AWG Copper (75°C column = 100A). Because this is over 100A (or larger than 1 AWG if you used 1 AWG), you are permitted to use the 75°C column if your panel lugs are rated for it.

Derating: When Your Base Ampacity Drops

The ampacities in the chart above assume perfect conditions: 30°C ambient air and no more than three current-carrying conductors bundled together. When you deviate from this, how derating rows modify the base value becomes critical to prevent melting insulation inside conduit.

Ambient Temperature Correction (NEC 310.15(B)(1)):
If your conduit runs across a 110°F (43°C) garage ceiling, you cannot use the 30°C base. You must multiply the 90°C column base value by the correction factor. For 41-45°C ambient, the factor is 0.87.

Conductor Bundling (NEC 310.15(C)(1)):
If you pull two separate 120V circuits (4 current-carrying conductors total: 2 hots, 2 neutrals) through the same EMT conduit, the wires heat each other up. You must multiply the 90°C column base value by 80%.

Worked Numeric Example:
You are pulling 10 AWG THHN for two circuits (4 current-carrying conductors) in a standard 75°F basement.
1. Base ampacity from 90°C column for 10 AWG = 40A.
2. Bundling derating for 4 conductors = 80%.
3. 40A × 0.80 = 32A derated ampacity.
4. Final check: 32A is greater than your 30A breaker. The installation is safe and code-compliant.

Decision Tree: Picking Your Exact Wire and Breaker

Use this if-then path to terminate your sizing process with a concrete pick. Do not guess; follow the logic.

Installation Scenario Condition / Constraint Concrete Pick (Wire & Breaker)
Standard 120V wall receptacle (bedroom/living room) 15A or 20A circuit, NM-B cable in walls 14 AWG NM-B on 15A OR 12 AWG NM-B on 20A
240V EV Charger (Hardwired) 40A continuous load (requires 125% sizing = 50A capacity), THHN in conduit 6 AWG THHN Copper on 50A breaker (6 AWG 75°C col is 65A, easily handles the 50A requirement)
100A Subpanel Feeder (Under 50 feet) 4 wires in conduit, standard 75°C panel lugs 3 AWG THHN Copper on 100A breaker (Using 75°C column: 100A)
100A Subpanel Feeder (Over 100 feet) Voltage drop becomes the limiting factor, not thermal ampacity 1/0 AWG THHN Copper on 100A breaker (Upsized strictly to maintain <3% voltage drop)

What This Chart Cannot Tell You

While NEC Table 310.16 is the bible for thermal limits, relying on it blindly will lead to three specific field failures:

  1. Voltage Drop: The NEC does not strictly enforce voltage drop for most branch circuits (it's an informational note, not a mandatory rule, except for specific feeders). However, running 14 AWG wire 150 feet to a 10A landscape lighting transformer will result in a massive voltage drop, causing lights to dim and motors to overheat. For runs over 75 feet, always calculate voltage drop and upsize the wire by at least one AWG step.
  2. Physical Lug Fitment: The chart might tell you that 2 AWG copper is perfect for a 115A load. But if the 100A main breaker lug in your panel is only physically rated to accept a maximum of 4 AWG wire, you cannot force the 2 AWG into it. You must either use a lug extender or downsize to aluminum (which has a larger diameter for the same ampacity, but requires different anti-oxidant paste and torque specs).
  3. Aluminum vs. Copper: This chart is exclusively for copper. If you are using aluminum SER cable for a subpanel feeder (which is highly recommended for cost savings on large gauges), you must look at the aluminum section of Table 310.16. As a rough rule of thumb, aluminum requires a wire size two AWG steps larger than copper for the same ampacity (e.g., 2 AWG Aluminum replaces 4 AWG Copper for an 85A-90A range).