Wire-Sizing & DC Voltage-Drop Reference (ASIC Miners & Solar)

Wire sizing for a mining circuit comes down to two questions that have to be answered together: can the conductor safely carry the current without overheating (ampacity), and will it deliver usable voltage at the far end of the run (voltage drop)? This reference pairs the published ampacity figures from NEC 2023 Table 310.16 with the DC resistance values from Chapter 9, Table 8, so you can check both at once for copper and aluminum from 14 AWG up to 4/0. The numbers are the code values, not estimates — but they are a starting point for planning, not a substitute for a licensed electrician signing off on your install.

How to read the ampacity columns

Every conductor in the table shows three ampacities — the 60 °C, 75 °C, and 90 °C insulation columns. The temperature does not describe how hot your room is; it describes the insulation rating of the wire and, more importantly, the rating of the terminals it lands on. You must size to the lowest temperature rating in the path. Most breakers, lugs, and equipment terminals are rated 75 °C, so the 75 °C column is the realistic limit for the majority of installs even when the wire itself is rated 90 °C THHN.

Two further rules trim the headline numbers down. For small conductors, NEC 240.4(D) caps the overcurrent device regardless of the ampacity column: 14 AWG copper is limited to 15 A, 12 AWG copper to 20 A, and 10 AWG copper to 30 A. And before you commit to a size, the ampacity must still be derated for ambient heat and for bundling several current-carrying conductors together, per NEC 310.15. A run inside a hot, crowded conduit behind a row of machines carries less than the table suggests.

Working the DC voltage-drop math

The resistance column is the second half of the calculation. For a DC run, voltage drop across the pair of conductors is Vdrop = 2 × L × I × R / 1000, where L is the one-way length of the run in feet, I is the current in amps, and R is the DC resistance in ohms per 1000 feet from the table. The factor of two accounts for current travelling out on one conductor and back on the other.

A common planning target is to keep any single branch circuit at or below a 3% drop and the whole path — feeder plus branch — at or below 5%. On a long DC home-run to a low-voltage device, voltage drop, not ampacity, is usually what forces you up to a heavier conductor. If your calculated drop creeps past target, step up one wire size and recompute rather than accepting marginal voltage at the load. The resistance figures shown are taken at 75 °C; a warmer conductor has slightly higher resistance and a touch more drop, which is a sensible direction to err.

Copper, aluminum, and the Canadian context

Aluminum carries roughly the same job at a lighter weight and lower cost, but at any given size it has lower ampacity and higher resistance than copper — so an aluminum run typically lands one or two sizes larger than the copper equivalent for the same load and length. Aluminum also demands proper terminations: listed connectors, an anti-oxidant where specified, and torque to the marked value. Note that NEC Table 310.16 does not list aluminum smaller than 12 AWG, so for the smallest circuits copper is the practical choice.

If you are wiring in Canada, the Canadian Electrical Code governs: Table 2 for copper and Table 4 for aluminum. The CEC ampacities are comparable to the NEC figures with minor differences, but the CEC and your local authority having jurisdiction always take precedence over any table reproduced here. Treat this page as a way to plan and sanity-check a run, then have a licensed electrician verify the final conductor size, overcurrent protection, derating, and terminations for your specific installation.