What the tool does
Most voltage drop calculators take one circuit at a time and give a number without saying which limit applies or how it was worked out. The tool checks a whole schedule and shows the working.
- Circuits: DC, single-phase two-wire and three-wire, three-phase three-wire and four-wire; load in A, kW or kVA with cos φ; copper or aluminium; parallel conductors; mm² (IEC or JIS sizes) or AWG and kcmil; length in m or ft.
- Feeders and circuits: set which feeder a circuit hangs on, and the drop is added from the origin to every load.
- Limits with the clause: KEC 232.3.9, IEC 60364-5-52 Annex G, IS 732 Table 47, NEC informational notes, AS/NZS 3000 3.6.2 and NBR 5410 6.2.7, for lighting and other uses and for supply from the network or your own transformer. For 内線規程 1310 and other documents you enter the limits yourself.
- Three methods: R and X (K × I × L × (R cos φ + X sin φ)), the simplified coefficients 35.6, 30.8 and 17.8 used in Korea and Japan, and mV/A/m values from your tables.
- Size and protection: with size "Automatic" the smallest size that passes is chosen; with your ampacity table the tool also checks Ib ≤ In ≤ Iz and I2 ≤ 1.45 Iz with the correction factors you enter, and gives the longest run within the limit.
- Report: a PDF with the settings, the clause, one line per circuit and the formula with the values for each circuit, a workbook whose drop, percentage, running total and result are live formulas, and CSV.
How to use it
- Choose the standard and how the installation is supplied.
- Enter or paste the circuits, set "Fed from" for circuits on a sub-board, and leave the size on "Automatic" or choose one.
- In "Cable table", enter the ampacity for your installation method from your standard or the cable maker, with R, X or mV/A/m if you have them.
- Read the checks per circuit and change sizes, lengths or devices.
- Export the report PDF or the workbook.
What is built in and what you enter
Built in: the formulas, the conductor resistance of IEC 60228 class 2 conductors at 20 °C, the temperature coefficients of copper and aluminium, and the limit percentages of public documents with their clause. Not built in: the limits of 内線規程, and ampacity and correction factor tables. They belong to the standards bodies, so you enter the values from the edition you work to; the report names the table you used.
How it was checked
Before every release the engine is run on published worked examples: a three-phase 200 V, 40 A, 100 m run on 38 mm² cable with R 0.626 and X 0.0955 Ω/km at cos φ 0.85 gives 4.0 V, about 2.0 % (Fujikura-Dia); 17.8 × 200 m × 250 A / (1000 × 150 mm²) gives 5.93 V; 35.6 × 30 m × 20 A / (1000 × 2 mm²) gives 10.68 V; and 0.61 mV/A/m at 250 A over 100 m stays within 4 % of 415 V (Prysmian). The limits are tested clause by clause, and the protection checks with a small table.
Limits
The tool is for low-voltage circuits. It does not compute short-circuit currents, earth fault loop impedance, disconnection times, motor starting drop or harmonics, and it does not derive ampacity from the installation method. Check the design against the standard that applies and the cable maker's data.
Last checked 2026-10-20