When you need to determine the maximum safe current for a copper conductor, the definitive reference is the electrical wire size chart derived from NEC Table 310.16. For standard residential branch circuits, the baseline rules are simple: 14 AWG handles 15 amps, 12 AWG handles 20 amps, 10 AWG handles 30 amps, and 6 AWG handles 55 amps (commonly used for 50-amp circuits). However, simply matching a breaker size to a wire gauge without understanding temperature columns and derating factors is a fast track to tripped breakers, melted insulation, or failed inspections.
How to Read the Electrical Wire Size Chart
The NEC ampacity tables are divided into temperature columns—typically 60°C (140°F), 75°C (167°F), and 90°C (194°F). These columns represent the maximum temperature the wire's insulation can safely withstand before degrading. To use the chart correctly, you must know which column applies to your specific installation.
According to NEC 110.14(C), for circuits rated 100A or less, you must use the 60°C column unless the equipment (breakers, lugs, receptacles) is explicitly rated for 75°C. Most modern residential breakers and terminals are rated 75°C, allowing you to use the 75°C column for THHN/THWN wire in conduit. However, if you are using NM-B (Romex) cable, the outer jacket limits the entire assembly to the 60°C column, regardless of the fact that the individual THHN wires inside the jacket have a 90°C rating.
Another critical rule is NEC 240.4(D), which imposes strict overcurrent protection limits on small conductors. Even if the chart shows a higher ampacity for 14, 12, or 10 AWG wire in the 75°C or 90°C columns, the maximum breaker size you can use is 15A, 20A, and 30A respectively. These hard limits override the chart's base ampacity for branch circuit protection.
Complete Copper Wire Ampacity Chart (NEC Table 310.16)
Below is the complete reference chart for copper conductors with common insulation types. We have included anchor links for the most frequently queried breaker sizes so you can bookmark this section for quick jobsite lookups.
Quick Jumps: 15A (14 AWG) | 20A (12 AWG) | 30A (10 AWG) | 40A/50A (8 AWG) | 50A/60A (6 AWG) | 70A/85A (4 AWG) | 100A (2 AWG)
| AWG / kcmil | 60°C Column (NM-B / TW / UF) | 75°C Column (THHW / THWN / XHHW) | 90°C Column (THHN / THWN-2) |
|---|---|---|---|
| 14 | 15A* | 20A* | 25A* |
| 12 | 20A* | 25A* | 30A* |
| 10 | 30A* | 35A* | 40A* |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 110A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
Derating Factors and What the Chart Cannot Tell You
The electrical wire size chart above assumes ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When real-world conditions deviate from this baseline, you must apply derating factors.
How Derating Modifies the Base Value:
Derating is calculated using the 90°C column, even if your termination limits you to the 75°C column. For example, if you pull four current-carrying 10 AWG THHN wires through a single conduit, NEC Table 310.15(C)(1) requires an 80% adjustment factor. You take the 90°C base ampacity for 10 AWG (40A) and multiply it by 0.80, resulting in a derated ampacity of 32A. Because 32A is less than the 75°C column value (35A), your final allowable ampacity is 32A. You cannot put this on a standard 35A breaker (which doesn't exist), so you must protect it at 30A.
What the Table Cannot Tell You:
The ampacity chart is completely blind to voltage drop. It only tells you the current required to melt the insulation or start a fire; it does not guarantee that your equipment will receive adequate voltage at the end of the run. According to Southwire's engineering guidelines and NEC informational notes, a voltage drop exceeding 3% on a branch circuit (or 5% total from service to load) can cause motors to overheat and electronics to malfunction. If you are running a 30-amp circuit to a detached garage 150 feet away, the chart says 10 AWG is fine for ampacity, but voltage drop calculations will force you to upsize to 6 AWG or 4 AWG to maintain usable voltage at the receptacle. Furthermore, the chart cannot tell you if a 2 AWG wire will physically fit into the lug of a specific 100-amp breaker; always verify terminal wire-range specifications on the equipment label.
Electrical Wire Size Chart FAQs
What size wire do I need for a 50 amp breaker according to the chart?
You need 6 AWG copper wire. Looking at the 75°C column, 6 AWG has an ampacity of 65A, which safely accommodates a 50A breaker. While 8 AWG wire has an ampacity of exactly 50A in the 75°C column, NEC 210.19(A)(1) requires conductors to be sized at 125% of continuous loads (loads expected to run for 3 hours or more). Because many 50A loads (like EV chargers or large heaters) are continuous, the wire must be rated for 62.5A (50A x 1.25). Therefore, 8 AWG is insufficient for continuous 50A loads, making 6 AWG the standard, code-compliant choice.
Why does the electrical wire size chart show higher amps for 90°C wire?
The 90°C column exists primarily to give you a higher baseline for derating calculations, not for direct termination. You are almost never allowed to use the 90°C ampacity as your final circuit rating because standard breakers, receptacles, and disconnects are not rated to withstand 90°C heat at their terminals. The workflow is to start with the 90°C value, apply your ambient temperature and conduit fill derating factors, and then compare that result to the 75°C or 60°C column. Your final allowable ampacity is the lowest number produced by this comparison.
Does the wire size chart apply to aluminum conductors?
No, the chart provided above is strictly for copper. Aluminum has a higher electrical resistance than copper, meaning it generates more heat at the same current level and requires a larger physical cross-section to carry the same load safely. For example, while 3 AWG copper is rated for 100A in the 75°C column, you would need 1 AWG aluminum to achieve the same 100A rating. If you are sizing aluminum wire (commonly used for service entrance feeders or long underground runs to save money), you must consult the aluminum-specific columns in NEC Table 310.16 and ensure your terminals are explicitly rated for aluminum (ALR) or use appropriate bi-metallic lugs to prevent galvanic corrosion.
