Wire size for 70 A over 75 ft on a 48 V system
| Circuit power70 A × 48 V | 3,360W |
|---|---|
| Conductor length75 ft out and 75 ft back | 150ft |
| Ampacity alone would allow6.74% drop — legal on heat, not acceptable on drop | 4 AWG |
| Power lost in the cable2.67% of what you are sending | 89.7W |
| — Voltage drop by size — | |
| 14 AWGnot rated for 70 A — 15 A max | — |
| 12 AWGnot rated for 70 A — 20 A max | — |
| 10 AWGnot rated for 70 A — 30 A max | — |
| 8 AWGnot rated for 70 A — 50 A max | — |
| 6 AWGnot rated for 70 A — 65 A max | — |
| 4 AWG85 A rated, drop too high | 6.74%3.23 V |
| 2 AWG115 A rated, drop too high | 4.24%2.04 V |
| 1/0 AWG150 A rated | 2.67%1.28 V |
| 2/0 AWG175 A rated | 2.12%1.02 V |
| 4/0 AWG230 A rated | 1.33%0.64 V |
- Current
- 70 A
- One-way distance
- 75 ft
- System voltage
- 48 V
Ampacity and voltage drop are two different questions
Ampacity asks whether the wire gets hot enough to be dangerous. Voltage drop asks whether enough of the power arrives at the other end. On a low-voltage DC run they almost never give the same answer, and the bigger one wins.
For 70 A over 75 ft at 48 V, ampacity alone would allow 4 AWG. Voltage drop says 1/0 AWG — 2.67%, or 1.28 V of the 48 V you started with.
Why the distance doubles
Current goes out on one conductor and comes back on the other. The copper in the circuit is 150 ft, not 75 ft. Forgetting the return leg is how people arrive at exactly half the real drop.
Why it matters more than it sounds
3,360 W leaves the source. Undersized cable does not just waste a few percent — on a solar charge controller it means the battery never sees absorption voltage, never finishes a charge cycle, and sulphates its way to an early death while every meter in the system reads normal.
What is not in the table
Copper at 75 °C. Aluminium conducts about 60% as well — go up two sizes. Conduit fill, ambient temperature above 30 °C and bundled conductors all derate ampacity further.
Notes
- Two different answers, and the bigger one wins. 4 AWG carries 70 A without overheating, but it drops 6.74% over this distance. You need 1/0 AWG — sized by voltage drop, not by heat.
- 3% is the NEC informational recommendation for a branch circuit, not a hard rule. On a 48 V DC system it is already generous: 1.44 V of the 48 V you started with.
- Running at 48 V is doing a lot of work here. The same 3,360 W at 12 V would draw 280 A and need a far heavier cable.
- Figures are copper at 75 °C. Aluminium runs about 60% of copper conductivity — go up two sizes. Conduit fill, ambient temperature above 30 °C and bundling all derate ampacity further, and none of that is in this table.
Nearby sizes
- Wire size for 60 A over 75 ft on a 48 V system
- Wire size for 80 A over 75 ft on a 48 V system
- Wire size for 50 A over 75 ft on a 48 V system
- Wire size for 100 A over 75 ft on a 48 V system
- Wire size for 70 A over 60 ft on a 48 V system
- Wire size for 70 A over 100 ft on a 48 V system
- Wire size for 70 A over 50 ft on a 48 V system
- Wire size for 70 A over 125 ft on a 48 V system
- Wire size for 70 A over 75 ft on a 24 V system
- Wire size for 70 A over 75 ft on a 12 V system
Read more
- Roof Space for a 10 kW Array: Panel Area Is Not Roof AreaTwenty-five panels cover about 525 square feet. The roof they need is closer to 680, and the gap is mostly required by code rather than by geometry.
- Daily Solar Output by Region, and the Seasonal Swing Behind the AverageAn annual average tells you what the system produces over a year. It tells you almost nothing about December, and December is where the sizing arguments happen.
- How Many Panels for 1,000 kWh a MonthThe answer ranges from fifteen panels to thirty-four, for the same house using the same electricity. Location does most of that, panel wattage does the rest.
- Converting kW to Panels, and the Three Ratings That Get ConfusedThree different numbers on a solar quote are all measured in kilowatts and none of them mean the same thing. Knowing which is which makes quotes comparable.