300 kcmil Voltage Drop at 208V 3-Phase
This page provides detailed voltage drop analysis for 300 kcmil conductors operating at 208V 3-Phase (three-phase). The 300 kcmil copper conductor has a resistance of 0.0429 ohms per 1000 feet and an ampacity of 285 amps at 75 degrees C per NEC Table 310.16. Use the tables below to determine the voltage drop at any distance and amperage combination, or to find the maximum distance you can run 300 kcmil wire while staying within the NEC recommended voltage drop limits.
Maximum Distance for 300 kcmil at 208V 3-Phase
The table below shows the maximum one-way distance you can run 300 kcmil copper conductor at 208V 3-Phase for each amperage level while maintaining voltage drop at or below 3% (branch circuit) and 5% (feeder + branch combined). If your planned run exceeds these distances, you must use a larger wire gauge. These values assume three-phase power with a 1.732 multiplier in the voltage drop formula.
| Amperage | Max Distance (3%) | Max Distance (5%) | 3% Drop = 6.2V |
|---|---|---|---|
| 5A | 16796 ft | 27993 ft | 6.2 V |
| 10A | 8398 ft | 13996 ft | 6.2 V |
| 15A | 5598 ft | 9331 ft | 6.2 V |
| 20A | 4199 ft | 6998 ft | 6.2 V |
| 25A | 3359 ft | 5598 ft | 6.2 V |
| 30A | 2799 ft | 4665 ft | 6.2 V |
| 40A | 2099 ft | 3499 ft | 6.2 V |
| 50A | 1679 ft | 2799 ft | 6.2 V |
| 60A | 1399 ft | 2332 ft | 6.2 V |
| 80A | 1049 ft | 1749 ft | 6.2 V |
| 100A | 839 ft | 1399 ft | 6.2 V |
Voltage Drop Table — 300 kcmil Copper at 208V 3-Phase
Complete voltage drop matrix for 300 kcmil copper conductor at 208V 3-Phase. Each cell shows the voltage drop in volts and percentage. Cells in red exceed the 3% NEC recommendation for branch circuits. Cells within the green range are NEC compliant. This table uses the three-phase voltage drop formula with a conductor resistance of 0.0429 ohms per 1000 feet.
| Distance | 5A | 10A | 15A | 20A | 25A | 30A | 40A | 50A | 60A | 80A | 100A |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 25 ft | 0.0V 0.0% | 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% | 0.1V 0.1% | 0.2V 0.1% |
| 50 ft | 0.0V 0.0% | 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% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% |
| 75 ft | 0.0V 0.0% | 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% | 0.3V 0.2% | 0.5V 0.2% | 0.6V 0.3% |
| 100 ft | 0.0V 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% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.4% |
| 125 ft | 0.1V 0.0% | 0.1V 0.0% | 0.1V 0.1% | 0.2V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.4% | 0.9V 0.5% |
| 150 ft | 0.1V 0.0% | 0.1V 0.1% | 0.2V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.3V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.3% | 0.9V 0.4% | 1.1V 0.5% |
| 200 ft | 0.1V 0.0% | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.4% | 0.9V 0.4% | 1.2V 0.6% | 1.5V 0.7% |
| 250 ft | 0.1V 0.0% | 0.2V 0.1% | 0.3V 0.1% | 0.4V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.4% | 0.9V 0.5% | 1.1V 0.5% | 1.5V 0.7% | 1.9V 0.9% |
| 300 ft | 0.1V 0.1% | 0.2V 0.1% | 0.3V 0.2% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.3% | 0.9V 0.4% | 1.1V 0.5% | 1.3V 0.6% | 1.8V 0.9% | 2.2V 1.1% |
| 400 ft | 0.1V 0.1% | 0.3V 0.1% | 0.5V 0.2% | 0.6V 0.3% | 0.7V 0.4% | 0.9V 0.4% | 1.2V 0.6% | 1.5V 0.7% | 1.8V 0.9% | 2.4V 1.1% | 3.0V 1.4% |
| 500 ft | 0.2V 0.1% | 0.4V 0.2% | 0.6V 0.3% | 0.7V 0.4% | 0.9V 0.5% | 1.1V 0.5% | 1.5V 0.7% | 1.9V 0.9% | 2.2V 1.1% | 3.0V 1.4% | 3.7V 1.8% |
When to Use 300 kcmil at 208V 3-Phase
300 kcmil wire at 208V 3-Phase is appropriate for circuits where the amperage does not exceed 285 amps (copper, 75 degrees C) and the voltage drop at the planned distance stays within NEC recommendations. At short distances under 50 feet, 300 kcmil handles 228-amp loads with comfortable voltage drop margin. As the distance increases, the voltage drop grows proportionally, and at some point a larger gauge becomes necessary.
If 300 kcmil does not provide adequate voltage drop performance for your run distance, consider the next larger gauge. Each step up in wire size roughly doubles the maximum distance for the same voltage drop percentage. Alternatively, if the circuit operates at 120 volts and the distance is problematic, consider whether the load can be served by a 240-volt circuit instead, which halves the percentage voltage drop and doubles the effective run distance for the same wire gauge.
For aluminum conductors, 300 kcmil has an ampacity of 228 amps at 75 degrees C and a resistance of 0.0707 ohms per 1000 feet. The higher resistance means aluminum requires approximately 65% more distance correction compared to copper, often requiring an increase of one or two gauge sizes to match copper's voltage drop performance at the same distance.
Related Wire Sizes at 208V 3-Phase
Compare voltage drop performance across different wire gauges at 208V 3-Phase. Larger gauges have lower resistance and can run longer distances with less voltage drop.
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