8 AWG Wire — Ampacity & Voltage Drop
Complete specifications for 8 AWG conductors including ampacity ratings from NEC Table 310.16, resistance values from NEC Chapter 9 Table 8, and pre-computed voltage drop tables at multiple distances. The 8 AWG conductor has a cross-sectional area of 16,510 circular mils and a diameter of 0.1285 inches. Use the tables below for quick reference, or use the wire size calculator for custom parameters.
8 AWG Specifications
Ampacity Ratings (NEC Table 310.16)
| Material | 60°C | 75°C | 90°C |
|---|---|---|---|
| Copper | 40 A | 50 A | 55 A |
| Aluminum | 32 A | 40 A | 44 A |
Voltage Drop Table — 8 AWG Copper at 120V
The table below shows the voltage drop in volts and percentage for 8 AWG copper conductors at 120 volts, single-phase, at various distances and amperages. Cells highlighted in red exceed the NEC recommended 3% voltage drop limit for branch circuits. Use these values to quickly determine if 8 AWG is adequate for your 120-volt circuit at the planned distance, or if you need to upsize to a larger gauge.
| Distance | 15A | 20A | 30A | 40A | 50A | 60A |
|---|---|---|---|---|---|---|
| 25 ft | 0.6V 0.5% | 0.8V 0.7% | 1.2V 1.0% | 1.6V 1.3% | 1.9V 1.6% | 2.3V 1.9% |
| 50 ft | 1.2V 1.0% | 1.6V 1.3% | 2.3V 1.9% | 3.1V 2.6% | 3.9V 3.2% | 4.7V 3.9% |
| 75 ft | 1.8V 1.5% | 2.3V 1.9% | 3.5V 2.9% | 4.7V 3.9% | 5.8V 4.9% | 7.0V 5.8% |
| 100 ft | 2.3V 1.9% | 3.1V 2.6% | 4.7V 3.9% | 6.2V 5.2% | 7.8V 6.5% | 9.3V 7.8% |
| 125 ft | 2.9V 2.4% | 3.9V 3.2% | 5.8V 4.9% | 7.8V 6.5% | 9.7V 8.1% | 11.7V 9.7% |
| 150 ft | 3.5V 2.9% | 4.7V 3.9% | 7.0V 5.8% | 9.3V 7.8% | 11.7V 9.7% | 14.0V 11.7% |
| 200 ft | 4.7V 3.9% | 6.2V 5.2% | 9.3V 7.8% | 12.4V 10.4% | 15.6V 13.0% | 18.7V 15.6% |
| 250 ft | 5.8V 4.9% | 7.8V 6.5% | 11.7V 9.7% | 15.6V 13.0% | 19.4V 16.2% | 23.3V 19.4% |
| 300 ft | 7.0V 5.8% | 9.3V 7.8% | 14.0V 11.7% | 18.7V 15.6% | 23.3V 19.4% | 28.0V 23.3% |
| 400 ft | 9.3V 7.8% | 12.4V 10.4% | 18.7V 15.6% | 24.9V 20.8% | 31.1V 25.9% | 37.3V 31.1% |
| 500 ft | 11.7V 9.7% | 15.6V 13.0% | 23.3V 19.4% | 31.1V 25.9% | 38.9V 32.4% | 46.7V 38.9% |
Voltage Drop Table — 8 AWG Copper at 240V
The following table shows voltage drop for 8 AWG copper conductors at 240 volts, single-phase. Because 240-volt circuits have a higher supply voltage, the percentage voltage drop is lower for the same absolute voltage loss. This means 8 AWG wire can run longer distances on a 240-volt circuit before exceeding the 3% limit compared to a 120-volt circuit carrying the same current.
| Distance | 15A | 20A | 30A | 40A | 50A | 60A |
|---|---|---|---|---|---|---|
| 25 ft | 0.6V 0.2% | 0.8V 0.3% | 1.2V 0.5% | 1.6V 0.7% | 1.9V 0.8% | 2.3V 1.0% |
| 50 ft | 1.2V 0.5% | 1.6V 0.7% | 2.3V 1.0% | 3.1V 1.3% | 3.9V 1.6% | 4.7V 1.9% |
| 75 ft | 1.8V 0.7% | 2.3V 1.0% | 3.5V 1.5% | 4.7V 1.9% | 5.8V 2.4% | 7.0V 2.9% |
| 100 ft | 2.3V 1.0% | 3.1V 1.3% | 4.7V 1.9% | 6.2V 2.6% | 7.8V 3.2% | 9.3V 3.9% |
| 125 ft | 2.9V 1.2% | 3.9V 1.6% | 5.8V 2.4% | 7.8V 3.2% | 9.7V 4.0% | 11.7V 4.9% |
| 150 ft | 3.5V 1.5% | 4.7V 1.9% | 7.0V 2.9% | 9.3V 3.9% | 11.7V 4.9% | 14.0V 5.8% |
| 200 ft | 4.7V 1.9% | 6.2V 2.6% | 9.3V 3.9% | 12.4V 5.2% | 15.6V 6.5% | 18.7V 7.8% |
| 250 ft | 5.8V 2.4% | 7.8V 3.2% | 11.7V 4.9% | 15.6V 6.5% | 19.4V 8.1% | 23.3V 9.7% |
| 300 ft | 7.0V 2.9% | 9.3V 3.9% | 14.0V 5.8% | 18.7V 7.8% | 23.3V 9.7% | 28.0V 11.7% |
| 400 ft | 9.3V 3.9% | 12.4V 5.2% | 18.7V 7.8% | 24.9V 10.4% | 31.1V 13.0% | 37.3V 15.6% |
| 500 ft | 11.7V 4.9% | 15.6V 6.5% | 23.3V 9.7% | 31.1V 13.0% | 38.9V 16.2% | 46.7V 19.4% |
How Far Can You Run 8 AWG?
One of the most common questions electricians and homeowners ask is how far a particular wire gauge can run before exceeding the NEC voltage drop recommendation. The answer depends on the circuit voltage, the current draw, and whether you are using the 3% branch circuit limit or the 5% feeder-plus-branch limit. Below are maximum one-way distances for 8 AWG copper at 3% voltage drop:
| Load | 120V Max Distance | 240V Max Distance |
|---|---|---|
| 15 Amps | 154 ft | 308 ft |
| 20 Amps | 115 ft | 231 ft |
| 30 Amps | 77 ft | 154 ft |
| 40 Amps | 57 ft | 115 ft |
| 50 Amps | 46 ft | 92 ft |
These distances represent the maximum one-way run from the breaker panel to the load. If your run exceeds these limits, you must use a larger wire gauge to keep the voltage drop within acceptable limits. For feeder circuits where the 5% combined limit applies, you can extend the run by approximately 67% beyond the 3% distances shown above, but only if the branch circuit portion stays within its own 3% allowance.
Common Uses for 8 AWG
8 AWG is rated for 40-50 amp circuits depending on the temperature rating and is commonly used for electric range circuits (40-amp), air conditioning compressor circuits, and larger workshop circuits. It is a stranded conductor in most applications, making it more flexible than solid 10-12 AWG wire but requiring ring terminals or proper torquing at connections.
When selecting 8 AWG for your installation, always verify that the ampacity meets or exceeds the circuit breaker rating, the voltage drop is within NEC recommendations for the run distance, and the terminations at both ends are rated for the conductor material and size. For circuits serving continuous loads (operating 3 hours or more), the conductor must be sized at 125% of the continuous load current. Consult NEC Article 210 for branch circuit requirements and Article 215 for feeder circuit requirements.
Other Wire Sizes
Browse specifications and voltage drop tables for other wire gauges. Selecting the correct wire size requires balancing ampacity, voltage drop, cost, and installation practicality.