500 kcmil Wire — Ampacity & Voltage Drop
Complete specifications for 500 kcmil 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 500 kcmil conductor has a cross-sectional area of 500,000 circular mils and a diameter of 0.707 inches. Use the tables below for quick reference, or use the wire size calculator for custom parameters.
500 kcmil Specifications
Ampacity Ratings (NEC Table 310.16)
| Material | 60°C | 75°C | 90°C |
|---|---|---|---|
| Copper | 320 A | 380 A | 430 A |
| Aluminum | 256 A | 304 A | 344 A |
Voltage Drop Table — 500 kcmil Copper at 120V
The table below shows the voltage drop in volts and percentage for 500 kcmil 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 500 kcmil 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 | 80A | 100A |
|---|---|---|---|---|---|---|---|---|
| 25 ft | 0.0V 0.0% | 0.0V 0.0% | 0.0V 0.0% | 0.1V 0.0% | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% |
| 50 ft | 0.0V 0.0% | 0.1V 0.0% | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.2% | 0.3V 0.2% |
| 75 ft | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.2% | 0.2V 0.2% | 0.3V 0.3% | 0.4V 0.3% |
| 100 ft | 0.1V 0.1% | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.2% | 0.3V 0.2% | 0.3V 0.3% | 0.4V 0.3% | 0.5V 0.4% |
| 125 ft | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.2% | 0.3V 0.2% | 0.3V 0.3% | 0.4V 0.3% | 0.5V 0.4% | 0.7V 0.5% |
| 150 ft | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.2% | 0.3V 0.3% | 0.4V 0.3% | 0.5V 0.4% | 0.6V 0.5% | 0.8V 0.7% |
| 200 ft | 0.1V 0.1% | 0.2V 0.2% | 0.3V 0.3% | 0.4V 0.3% | 0.5V 0.4% | 0.6V 0.5% | 0.8V 0.7% | 1.0V 0.9% |
| 250 ft | 0.2V 0.2% | 0.3V 0.2% | 0.4V 0.3% | 0.5V 0.4% | 0.7V 0.5% | 0.8V 0.7% | 1.0V 0.9% | 1.3V 1.1% |
| 300 ft | 0.2V 0.2% | 0.3V 0.3% | 0.5V 0.4% | 0.6V 0.5% | 0.8V 0.7% | 0.9V 0.8% | 1.2V 1.0% | 1.6V 1.3% |
| 400 ft | 0.3V 0.3% | 0.4V 0.3% | 0.6V 0.5% | 0.8V 0.7% | 1.0V 0.9% | 1.2V 1.0% | 1.6V 1.4% | 2.1V 1.7% |
| 500 ft | 0.4V 0.3% | 0.5V 0.4% | 0.8V 0.7% | 1.0V 0.9% | 1.3V 1.1% | 1.6V 1.3% | 2.1V 1.7% | 2.6V 2.1% |
Voltage Drop Table — 500 kcmil Copper at 240V
The following table shows voltage drop for 500 kcmil 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 500 kcmil 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 | 80A | 100A |
|---|---|---|---|---|---|---|---|---|
| 25 ft | 0.0V 0.0% | 0.0V 0.0% | 0.0V 0.0% | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.1% |
| 50 ft | 0.0V 0.0% | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.1% |
| 75 ft | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% |
| 100 ft | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% |
| 125 ft | 0.1V 0.0% | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.7V 0.3% |
| 150 ft | 0.1V 0.1% | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.8V 0.3% |
| 200 ft | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.8V 0.3% | 1.0V 0.4% |
| 250 ft | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.7V 0.3% | 0.8V 0.3% | 1.0V 0.4% | 1.3V 0.5% |
| 300 ft | 0.2V 0.1% | 0.3V 0.1% | 0.5V 0.2% | 0.6V 0.3% | 0.8V 0.3% | 0.9V 0.4% | 1.2V 0.5% | 1.6V 0.7% |
| 400 ft | 0.3V 0.1% | 0.4V 0.2% | 0.6V 0.3% | 0.8V 0.3% | 1.0V 0.4% | 1.2V 0.5% | 1.6V 0.7% | 2.1V 0.9% |
| 500 ft | 0.4V 0.2% | 0.5V 0.2% | 0.8V 0.3% | 1.0V 0.4% | 1.3V 0.5% | 1.6V 0.7% | 2.1V 0.9% | 2.6V 1.1% |
How Far Can You Run 500 kcmil?
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 500 kcmil copper at 3% voltage drop:
| Load | 120V Max Distance | 240V Max Distance |
|---|---|---|
| 15 Amps | 4651 ft | 9302 ft |
| 20 Amps | 3488 ft | 6976 ft |
| 30 Amps | 2325 ft | 4651 ft |
| 40 Amps | 1744 ft | 3488 ft |
| 50 Amps | 1395 ft | 2790 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 500 kcmil
500 kcmil copper is rated for 320-430 amps and is the largest standard conductor size covered in this reference. It is used for the largest commercial and industrial service entrances, main switchgear feeders, and utility-to-building service connections. Conductors of this size are nearly always installed using mechanical pulling equipment, and parallel runs of smaller conductors are often considered as an alternative for practical installation.
When selecting 500 kcmil 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.