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The expected current carried by the PV circuit conductor.
Use the module or string's rated operating current (or short-circuit current with the appropriate NEC factor applied), whichever your circuit is sized against.
The nominal DC system voltage of the PV circuit.
The array's nominal DC voltage — the string, not the inverter's AC output and not a single module's rating. Nominal is what this sizing works from, but it is not the number the equipment must survive: string voltage RISES as temperature falls, so the open-circuit voltage on the coldest morning of the year is what decides insulation and disconnect ratings. Size the conductor here, then check that cold figure separately.
The one-way distance from the source (e.g. array/combiner box) to the load (e.g. inverter/battery).
Don't double it for the return path — the formula already accounts for both directions.
The target maximum percentage of system voltage lost to conductor resistance.
PV designers commonly target 1-3% voltage drop on source/output circuits to limit energy loss.
The resistivity of the conductor material at its expected operating temperature.
Copper rises about four tenths of a percent per kelvin, so the figure at a conductor's rated temperature is materially higher than the 20 °C value printed in tables: roughly 0.0213 at 75 °C and 0.0223 at 90 °C. Sizing on the cold number understates the drop a loaded circuit will actually see. The field accepted nothing above 0.02 until this was corrected, which refused the very condition this help text asks you to use. This field wants the PER-METRE figure even when the distance box above has switched to US units: the distance carries a dimension and follows the unit toggle, while this rate carries none and stays exactly as typed. US practice quotes the same property per foot instead, as ohm-circular-mil per foot — the K of the per-foot voltage-drop method — and that number is not this one. Divide it by 601.5 to land in this field's unit: a square millimetre is 1973.5 circular mils and a foot is 0.3048 m, and 1973.5 × 0.3048 = 601.5. So 10.5 per foot is the 0.0175 above, and 12.8 per foot is the 0.0213. Typed in raw, any per-foot figure sits far above the 0.025 maximum here and is pulled back to 0.025 — you are told the highest accepted value was used, but not that the unit was wrong — and the defaults on this page (10 A, 48 V, 15 m one-way, 2%) then report 7.81 mm² where the truth is 5.47 mm², 43% more copper than the drop target asks for. Worse, 10.5 and 12.8 both clamp to that same 0.025, so the operating temperature you chose disappears with them; this field's entire 0.015-0.025 range spans only 9.0 to 15.0 per foot.
Minimum conductor cross-sectional area
0.00844 in²
Convert the resulting minimum cross-sectional area to the next larger standard wire gauge (AWG) or metric conductor size — do not round down. Also verify the selected conductor's ampacity rating (NEC Table 310.16, with appropriate temperature/conduit fill derating) independently meets or exceeds the circuit current.
They open the calculator with your figures already in it
Solar Panel PV Wire Sizing Calculator: 0.0084 in² — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Conductor area = (2 x resistivity x one-way distance x current) ÷ maximum allowable voltage drop, the standard DC circuit voltage-drop sizing method applied to a solar PV source/output circuit run (the factor of 2 accounts for the round-trip conductor length)
Inputs used
- Circuit Current (A)
- 10
- System Voltage (V)
- 48
- One-Way Conductor Distance
- 49 ft
- Maximum Allowable Voltage Drop (%)
- 2
- Copper Resistivity (Ω·mm²/m, ~0.0175 at 20°C, ~0.0213 at 75°C)
- 0.02
Confidence note: Convert the resulting minimum cross-sectional area to the next larger standard wire gauge (AWG) or metric conductor size — do not round down. Also verify the selected conductor's ampacity rating (NEC Table 310.16, with appropriate temperature/conduit fill derating) independently meets or exceeds the circuit current.
What this calculation does not cover
- Voltage drop is not ampacity, and none of the code side of the job is done here. The current is used exactly as typed, with no PV multiplier applied to it, no fuse or breaker sized, and no account taken of the temperature rating of the terminals the conductor lands in. A size that meets this drop target can still be thermally inadequate and non-compliant.
- Copper only. The resistivity field spans copper from cold to a conductor at its rated temperature; aluminium is about 1.6 times as resistive and does not fit inside that range, so an aluminium run has to be sized against the aluminium figure and comes out roughly two AWG sizes larger for the same drop.
- Nothing raises the resistivity for how hot the conductor actually gets. The figure is whatever you enter, so leaving the 20 °C (68 °F) table value in place understates the drop of a loaded circuit sitting in conduit on a sunlit roof by around a fifth against the 75 °C (167 °F) figure.
- Conductor metal only. MC4 connectors, fuse holders, breakers, combiner busbars and every termination in the run add resistance the formula never sees, so an assembled circuit drops more than the copper alone accounts for.
- This models a two-wire DC circuit carrying its full current over the whole run. It does not describe the inverter's AC output circuit, where reactance, power factor and the three-phase multiplier replace the factor of two, and it does not describe a home run that picks up further strings along its length.
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This result is a specification — 0.00844 in² — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-05 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Conductor area = (2 x resistivity x one-way distance x current) ÷ maximum allowable voltage drop, the standard DC circuit voltage-drop sizing method applied to a solar PV source/output circuit run (the factor of 2 accounts for the round-trip conductor length)
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