If you need a quick wire chart for amps to size your next branch circuit or feeder, the table below provides the exact ampacities for copper and aluminum conductors based on NEC Table 310.16. For standard residential branch circuits under 40 amps, use the 60°C or 75°C column depending on your cable type. For larger feeders or individual THHN wires in conduit, the 75°C column is your baseline for sizing, while the 90°C column is used strictly for derating calculations.
How to Read This Wire Chart for Amps
Before pulling wire, you must understand which column applies to your specific installation. The National Electrical Code (NEC) dictates that the allowable ampacity of a circuit is limited by the lowest temperature rating of any connected device, termination, or conductor in the loop. This is known as the 'weakest link' rule.
Most standard residential breakers and receptacles are rated for 75°C terminations. Even if you pull 90°C THHN wire through your conduit, you must size your overcurrent protection based on the 75°C column. You only use the 90°C column to apply derating factors before checking the final ampacity against the 75°C column.
Here is how to navigate the columns:
- 60°C Column (TW/UF): Used for non-metallic sheathed cable (NM-B/Romex) and UF-B direct burial cable, as NEC 334.80 restricts these to the 60°C ampacity regardless of the wire's actual insulation rating.
- 75°C Column (THHW/THWN/XHHW): The standard baseline for sizing most feeders and branch circuits using individual conductors in conduit, assuming 75°C terminations.
- 90°C Column (THHN/THWN-2): Used exclusively as the starting point for ambient temperature corrections and bundling derating calculations.
Master AWG Wire Chart for Amps (NEC Table 310.16)
The following data is extracted from NEC Table 310.16 (applicable through the 2023 and upcoming 2026 code cycles). It assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.
| AWG / kcmil | Copper 60°C (TW/UF) | Copper 75°C (THWN) | Copper 90°C (THHN) | Aluminum 75°C (XHHW) | Aluminum 90°C (THHN) |
|---|---|---|---|---|---|
| 14 | 15A* | 20A* | 25A* | - | - |
| 12 | 20A* | 25A* | 30A* | - | - |
| 10 | 30A | 35A | 40A | - | - |
| 8 | 40A | 50A | 55A | 40A | 45A |
| 6 | 55A | 65A | 75A | 50A | 60A |
| 4 | 70A | 85A | 95A | 65A | 75A |
| 3 | 85A | 100A | 110A | 75A | 85A |
| 2 | 95A | 115A | 130A | 90A | 100A |
| 1 | 110A | 130A | 145A | 100A | 120A |
| 1/0 | 125A | 150A | 170A | 120A | 135A |
| 2/0 | 145A | 175A | 195A | 135A | 150A |
| 3/0 | 165A | 200A | 225A | 155A | 170A |
| 4/0 | 195A | 230A | 260A | 180A | 205A |
*Note: While the table lists higher ampacities for 14, 12, and 10 AWG in the 75°C and 90°C columns, NEC 240.4(D) strictly limits overcurrent protection for these small conductors to 15A, 20A, and 30A respectively, unless specific motor or welding exceptions apply.
Bookmark-Friendly Quick-Jump Rows
- 20 Amp Circuit: 12 AWG Copper (NM-B or THHN). Do not use 14 AWG.
- 30 Amp Circuit: 10 AWG Copper. Common for dryers and RV receptacles.
- 50 Amp Circuit: 6 AWG Copper (NM-B) or 8 AWG Copper (THHN in conduit with 75°C terminations). For aluminum, use 4 AWG.
- 100 Amp Subpanel Feeder: 3 AWG Copper or 1 AWG Aluminum (SER cable or THHN in conduit).
- 200 Amp Service Entrance: 2/0 AWG Copper or 4/0 AWG Aluminum.
Derating and Edge Cases: What the Table Cannot Tell You
A base wire chart for amps assumes ideal conditions: 86°F (30°C) ambient temperature and no more than three current-carrying conductors bundled together. When real-world conditions deviate, you must apply derating factors. This is where the 90°C column becomes critical.
How derating rows modify the base value:
If you pull four current-carrying conductors through a single conduit, NEC Table 310.15(C)(1) requires you to multiply the base ampacity by 80%. You always start this math using the 90°C column.
You are pulling four 10 AWG THHN copper wires in a conduit for a multi-wire branch circuit.
1. Base 90°C ampacity for 10 AWG = 40A.
2. Derating factor for 4 conductors = 80%.
3. 40A × 0.80 = 32A adjusted ampacity.
4. Because 32A is still greater than the 75°C column limit (35A) and standard breaker sizes, you can still protect this wire with a standard 30A breaker. If you had six conductors (derated to 50%, yielding 20A), you would be forced to upsize to 8 AWG wire.
What the table cannot tell you:
The ampacity table completely ignores voltage drop. If you are running a 120V circuit 150 feet to a detached garage, a 12 AWG wire might safely carry 20A without melting, but the voltage at the far end will drop below 114V, causing motors to overheat and lights to dim. For runs over 100 feet, always calculate voltage drop (aiming for <3% on branch circuits) and upsize the wire accordingly, regardless of what the ampacity chart dictates. Tools like the EC&M voltage drop calculators are essential for long feeder runs.
Wire Sizing FAQ
What wire size do I need for a 50 amp breaker according to a standard wire chart for amps?
For a 50-amp breaker, you need 6 AWG copper wire if you are using NM-B (Romex) cable, because you must use the 60°C column (which rates 6 AWG at 55A, sufficient for a 50A load). If you are pulling individual THHN conductors in conduit and your terminations are rated 75°C, you can use 8 AWG copper (rated 50A in the 75°C column). If using aluminum SER cable, you must step up to 4 AWG.
Why does my wire chart for amps show different values for THHN and NM-B cable?
THHN is an individual wire insulation rated for 90°C, while NM-B is a multi-conductor cable jacketed in PVC. The NEC restricts NM-B cable to the 60°C ampacity column (NEC 334.80) because the heat generated by multiple current-carrying conductors bundled tightly inside a non-metallic sheath cannot dissipate as efficiently as individual wires spaced apart inside an open conduit. Therefore, 8 AWG NM-B is limited to 40A, while 8 AWG THHN in conduit can handle 50A or 55A depending on the termination rating.
How do I adjust my wire chart for amps when running conductors through a hot attic?
If your attic reaches 110°F (43°C) in the summer, you must apply an ambient temperature correction factor. Using the 90°C column for THHN wire, the correction factor for 105°F-113°F is 87%. If you are using 10 AWG THHN (base 40A), the adjusted ampacity becomes 34.8A (40 × 0.87). You then compare this derated value to the 75°C column to ensure it still meets your breaker size requirements. If the attic exceeds 122°F (50°C), the derating becomes severe (82%), and you will likely need to upsize your wire.
Can I use the 90°C column on the wire chart for amps to size my circuit breaker?
No. Almost no standard residential breakers, lugs, or receptacles are rated for 90°C terminations. The 90°C column is strictly a mathematical starting point for derating (adjusting for heat and bundling). Once you have calculated your derated ampacity using the 90°C column, you must verify that the final number is equal to or greater than the ampacity listed in the 75°C (or 60°C) column for your chosen breaker size. You cannot use the raw 90°C number to justify a larger breaker.
