Wire size for 175 A over 15 ft on a 12 V system
| Circuit power175 A × 12 V | 2,100W |
|---|---|
| Conductor length15 ft out and 15 ft back | 30ft |
| Ampacity alone would allow4.23% drop — legal on heat, not acceptable on drop | 2/0 AWG |
| Power lost in the cable2.66% of what you are sending | 55.9W |
| — Voltage drop by size — | |
| 14 AWGnot rated for 175 A — 15 A max | — |
| 12 AWGnot rated for 175 A — 20 A max | — |
| 10 AWGnot rated for 175 A — 30 A max | — |
| 8 AWGnot rated for 175 A — 50 A max | — |
| 6 AWGnot rated for 175 A — 65 A max | — |
| 4 AWGnot rated for 175 A — 85 A max | — |
| 2 AWGnot rated for 175 A — 115 A max | — |
| 1/0 AWGnot rated for 175 A — 150 A max | — |
| 2/0 AWG175 A rated, drop too high | 4.23%0.51 V |
| 4/0 AWG230 A rated | 2.66%0.32 V |
- Current
- 175 A
- One-way distance
- 15 ft
- System voltage
- 12 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 175 A over 15 ft at 12 V, ampacity alone would allow 2/0 AWG. Voltage drop says 4/0 AWG — 2.66%, or 0.32 V of the 12 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 30 ft, not 15 ft. Forgetting the return leg is how people arrive at exactly half the real drop.
Why it matters more than it sounds
2,100 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. 2/0 AWG carries 175 A without overheating, but it drops 4.23% over this distance. You need 4/0 AWG — sized by voltage drop, not by heat.
- 3% is the NEC informational recommendation for a branch circuit, not a hard rule. On a 12 V DC system it is already generous: 0.36 V of the 12 V you started with.
- 12 V is what makes this expensive. The same 2,100 W at 24 V halves the current and quarters the loss — the cheapest way out of a big cable bill is almost always a higher system voltage.
- 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 150 A over 15 ft on a 12 V system
- Wire size for 200 A over 15 ft on a 12 V system
- Wire size for 125 A over 15 ft on a 12 V system
- Wire size for 175 A over 10 ft on a 12 V system
- Wire size for 175 A over 20 ft on a 12 V system
- Wire size for 175 A over 5 ft on a 12 V system
- Wire size for 175 A over 25 ft on a 12 V system
- Wire size for 175 A over 15 ft on a 24 V system
- Wire size for 175 A over 15 ft on a 48 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.