| What | Source, and its limits |
|---|---|
| Wire resistance | NEC Chapter 9, Table 8: DC resistance of stranded, uncoated copper and of aluminum at 75 °C. Real wire runs cooler most of the time, so real drop is usually a little lower. On AC, large conductors in steel conduit add reactance (NEC Table 9) that this tool does not include. |
| Voltage-drop formula | Single-phase and DC: 2 × one-way length × amps × resistance per foot. Three-phase: √3 × length × amps × resistance. The 3% and 5% targets are the NEC's informational-note recommendations, not code requirements. |
| Ampacity | NEC Table 310.16, 60 °C and 75 °C columns, for not more than three current-carrying conductors at 30 °C ambient. More conductors together, higher temperatures, and the temperature rating of the breaker and device terminals all reduce what a wire may carry. The 15, 20 and 30 A breaker limits on 14, 12 and 10 AWG copper are NEC 240.4(D). |
| Continuous loads | NEC 210.19 and 210.20: a load expected to run 3 hours or more is counted at 125% when sizing the breaker and wire (the 80% rule). |
| Battery runtime | Simple energy arithmetic (Wh = Ah × V, runtime = usable Wh ÷ watts drawn). It does not model Peukert loss, temperature, battery age, or a battery management system cutting out early, all of which shorten real runtime. |
| Appliance watts | The quick-add values are typical nameplate figures, not measurements of your appliance. Check the label; motor start-up current is not included. |
Results are rounded for display. The underlying math is done in full double precision.
This tool is provided free, as-is, without warranty of any kind, express or implied. It is offered for general information and convenience. The author is not liable for any loss, damage or injury arising from its use.
Nothing here constitutes electrical engineering, legal or other professional advice.