For standard residential and commercial copper wiring, the baseline AWG amperage matches are: 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, 8 AWG for 40A, and 6 AWG for 55A (often protected at 60A per specific NEC exceptions). These values are derived directly from NEC Table 310.16, the definitive standard for conductor ampacity in the United States. However, blindly matching a wire gauge to a breaker without checking the temperature column or derating factors is how terminals melt and insulation fails. This guide gives you the exact chart, explains which temperature column actually applies to your installation, and provides a concrete decision path to lock in your wire and breaker size.
How to Read the NEC AWG Amperage Table
The most common mistake DIYers and junior apprentices make is looking at the highest number in the table and sizing the breaker to it. The NEC Table 310.16 is divided into three temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). Here is exactly which column applies to your installation:
- The 60°C Column: You must use this column if you are using NM-B (Romex) cable, or if the wire is 14, 12, or 10 AWG, regardless of the insulation type. NEC 240.4(D) strictly limits these small conductors to 15A, 20A, and 30A respectively. Furthermore, NEC 334.80 dictates that NM-B cable ampacity is limited to the 60°C column, even though the individual wires inside are rated for 90°C.
- The 75°C Column: Use this column for individual THHN/THWN-2 conductors in conduit (sizes 8 AWG and larger) when terminating on standard modern breakers and lugs, which are almost universally rated for 75°C.
- The 90°C Column: Never use this column to size your breaker. The 90°C column is used exclusively as the starting baseline for derating calculations (adjusting for heat and bundling) before you apply the final breaker size.
Complete AWG Amperage Chart (NEC Table 310.16 Copper)
Below is the complete ampacity table for copper conductors with an ambient temperature of 30°C (86°F).
• 15 Amp Circuit: 14 AWG (60°C col)
• 20 Amp Circuit: 12 AWG (60°C col)
• 30 Amp Circuit: 10 AWG (60°C col)
• 50 Amp Circuit: 6 AWG (75°C col - 55A base, protected at 60A via 240.4(B) or sized to 50A standard breaker)
| AWG or kcmil | 60°C (140°F) NM-B & Small Wire |
75°C (167°F) THHN in Conduit |
90°C (194°F) Derating Baseline |
Standard Max Breaker |
|---|---|---|---|---|
| 14 | 15A | 20A | 25A | 15A |
| 12 | 20A | 25A | 30A | 20A |
| 10 | 30A | 35A | 40A | 30A |
| 8 | 40A | 50A | 55A | 40A |
| 6 | 55A | 65A | 75A | 60A* |
| 4 | 70A | 85A | 95A | 80A |
| 3 | 85A | 100A | 110A | 100A |
| 2 | 95A | 115A | 130A | 110A |
| 1 | 110A | 130A | 145A | 125A |
| 1/0 | 125A | 150A | 170A | 150A |
| 2/0 | 145A | 175A | 195A | 175A |
| 3/0 | 165A | 200A | 225A | 200A |
| 4/0 | 195A | 230A | 260A | 225A |
*Note on 6 AWG: While the 75°C ampacity is 65A, standard breaker sizes jump from 50A to 60A. NEC 240.4(B) allows you to round up to the next standard breaker size (60A) if the exact ampacity doesn't match a standard breaker, provided the load is not a multi-outlet branch circuit.
Derating: When Your Base Amperage Drops
The ampacities in the table above assume you have no more than three current-carrying conductors in a raceway and an ambient temperature of 30°C (86°F). When you bundle wires together in a conduit, they cannot dissipate heat effectively. This is where the 90°C column saves you, but it also reduces your final allowable amperage.
1. Count current-carrying conductors: The ground does not count. You have 3 current-carrying conductors. No derating required.
2. Add a second circuit: Now you have 6 current-carrying conductors (4 hots, 2 neutrals).
3. Apply NEC Table 310.15(C)(1): For 4 to 6 conductors, the adjustment factor is 80%.
4. Calculate: Start with the 90°C column for 12 AWG (30A). Multiply 30A × 0.80 = 24A.
5. Result: Your derated ampacity is 24A. Because this is still above the 20A breaker limit, you can safely use 12 AWG wire on a 20A breaker. If you added a third circuit (9 conductors, 70% derating: 30A × 0.70 = 21A), you would still pass, but you are getting dangerously close to the limit.
Decision Path: Pick Your Wire and Breaker in 4 Steps
Do not guess. Follow this exact decision tree to terminate your wire and breaker selection.
| Step | Action | Rule / Formula |
|---|---|---|
| 1. Determine Load Type | Is the load continuous (on for 3+ hours)? | If YES, multiply total amps by 1.25. If NO, use raw amps. |
| 2. Size the Breaker | Select the standard breaker size equal to or greater than Step 1. | Standard sizes: 15, 20, 30, 40, 50, 60, 70, 80, 90, 100A. |
| 3. Check Terminal Temp | Identify your cable type and breaker terminal rating. | NM-B = 60°C col. THHN in standard breaker = 75°C col. |
| 4. Pick the Wire | Find the AWG where the table value ≥ your breaker size. | Apply derating if >3 current-carrying wires in conduit. |
Concrete Pick Scenario: You are wiring a 16A continuous load (like a large window AC unit or a server rack) using individual THHN wires in conduit.
• Step 1: 16A × 1.25 = 20A.
• Step 2: The next standard breaker size is 20A.
• Step 3: THHN in a standard 75°C rated breaker means we use the 75°C column.
• Step 4: Looking at the 75°C column, 14 AWG is only 20A, but NEC 240.4(D) forbids 14 AWG on a 20A breaker. 12 AWG is rated 25A in the 75°C column, which easily covers the 20A breaker.
Final Result: Use 12 AWG copper THHN wire on a 20A breaker.
What This Table Cannot Tell You (Voltage Drop)
The AWG amperage chart dictates how much current a wire can carry before the insulation melts. It tells you absolutely nothing about whether the voltage will successfully reach the other end of the wire. According to copper conductivity standards, pushing 55A through 150 feet of 6 AWG wire will result in a massive voltage drop, starving your equipment and causing motors to overheat and fail.
As a hard rule for branch circuits: if your one-way wire distance exceeds 50 feet, you must calculate voltage drop. The NEC recommends a maximum 3% voltage drop on branch circuits and a 5% total drop from the service entrance to the furthest outlet. If your distance is long, you will need to upsizing your wire gauge (e.g., moving from 10 AWG to 8 AWG) purely to maintain voltage, even if the 10 AWG is perfectly safe from an ampacity and thermal standpoint. Always check distance before finalizing your wire purchase.
