When you are sizing branch circuits or feeders pulled through a raceway, the 75°C column of the NEC AWG ampacity copper in conduit 75C table is your baseline. Sourced directly from NEC Table 310.16 (formerly 310.15(B)(16)), this chart dictates the maximum continuous current a copper conductor can carry before its insulation begins to degrade.
The values below assume copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors bundled in the conduit. If your jobsite exceeds these parameters, you must apply derating factors, which we will cover below.
How to Read the NEC 310.16 Copper Ampacity Table (75°C Column)
The NEC provides three temperature columns for copper: 60°C, 75°C, and 90°C. Here is how to choose the right one for your installation:
- 60°C Column: Used primarily for NM-B (Romex) cable and older equipment where the termination rating is unknown or explicitly marked 60°C.
- 75°C Column: The standard for almost all modern THHN/THWN-2 wire pulled in conduit. Most circuit breakers and lugs rated 100A or less are tested and listed for 75°C terminations.
- 90°C Column: Rarely used for final ampacity sizing. It exists almost exclusively as the starting point for calculating derating adjustments (bundling and high ambient temperatures).
Below is the data-dense reference chart for the most commonly queried AWG sizes. Bookmark this section for quick bench lookups.
| AWG / kcmil | 60°C (NM-B) | 75°C (Conduit/THHN) | 90°C (Derating Base) |
|---|---|---|---|
| 14 AWG | 15A | 20A* | 25A |
| 12 AWG | 20A | 25A* | 30A |
| 10 AWG | 30A | 35A* | 40A |
| 8 AWG | 40A | 50A | 55A |
| 6 AWG | 55A | 65A | 75A |
| 4 AWG | 70A | 85A | 95A |
| 3 AWG | 85A | 100A | 115A |
| 2 AWG | 95A | 115A | 130A |
| 1 AWG | 110A | 130A | 145A |
| 1/0 AWG | 125A | 150A | 170A |
| 2/0 AWG | 145A | 175A | 195A |
| 3/0 AWG | 165A | 200A | 225A |
| 4/0 AWG | 195A | 230A | 260A |
Derating Rules: When Your Base Ampacity Drops
The numbers in the table above assume you have a maximum of three current-carrying conductors (e.g., one hot, one neutral, one ground) in your conduit. The moment you pull a fourth current-carrying conductor into that same raceway, the wires heat each other up, and the base ampacity drops. This is governed by NEC 310.15(C)(1).
Here is the adjustment factor schedule for bundling:
- 4 to 6 conductors: Multiply base ampacity by 80%
- 7 to 9 conductors: Multiply base ampacity by 70%
- 10 to 20 conductors: Multiply base ampacity by 50%
When calculating derating, you are allowed to use the 90°C column as your starting baseline, provided your wire insulation is rated for it (like THHN). However, the final derated number cannot exceed the 75°C column value for termination purposes.
Worked Example: You are pulling four current-carrying 8 AWG THHN copper wires through a single PVC conduit to feed a subpanel. What is your final ampacity and breaker size?
- Find the 90°C base: Table 310.16 lists 8 AWG at 55A in the 90°C column.
- Apply the adjustment factor: Four conductors require an 80% multiplier. (55A × 0.80 = 44A).
- Check the termination limit: The 75°C column for 8 AWG is 50A. Since our derated value (44A) is less than the termination limit (50A), the final allowable ampacity is 44A.
- Select the breaker: Per NEC 240.4(B), you can round up to the next standard breaker size, which is 45A.
If you had incorrectly used the 75°C column (50A) as your derating baseline, you would have calculated 40A (50A × 0.80), forcing you to use a 40A breaker and wasting the thermal headroom of your THHN insulation.
What This Table Cannot Tell You (And How to Compensate)
Relying solely on the AWG ampacity copper in conduit 75C table will lead to failed inspections or melted wires if you ignore the physical realities of your installation. The table is blind to three critical factors:
1. Terminal Temperature Limits (NEC 110.14(C))
Wire insulation might be rated for 90°C, but the lugs on your breaker and the bus bars in your panel likely are not. For equipment rated 100A or less, NEC 110.14(C) mandates that you must use the 60°C or 75°C column for your final sizing, regardless of the wire's insulation rating. You can only use the 90°C column for the derating math shown above; the final result must always be capped by the termination rating.
2. Voltage Drop Over Distance
Table 310.16 assumes the wire is short enough that resistance is negligible. If you are pulling a 6 AWG feeder 150 feet to a detached garage workshop, the wire might safely handle 65A thermally, but the voltage drop at the far end will starve your power tools. The NEC recommends (via Informational Note to 310.15) a maximum 3% voltage drop on branch circuits and 5% total from service to outlet. For long runs, use a voltage drop calculator and expect to upsize your wire by one or two AWG sizes beyond what the ampacity table demands.
3. Conduit Fill Capacity (NEC Chapter 9)
Just because four 4 AWG wires fit the ampacity requirements doesn't mean they will physically fit inside a 3/4-inch EMT conduit. NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. Jamming wires into an undersized conduit damages the THHN insulation during the pull and traps heat, effectively invalidating the 30°C ambient assumption of the ampacity table. Always cross-reference your wire count and AWG against the conduit fill tables in Chapter 9, Table 5 before buying your PVC or EMT.
For the most current updates on code cycles and specific local amendments, always consult the official NFPA 70 documentation and verify with your local Authority Having Jurisdiction (AHJ).
