Calculate voltage drop

Unlike the wire-sizing calculator, the cross-section here is an input, not a result: the calculator returns the drop in volts and percent, the power loss, and a comparison against both your own limit and the applicable standard's limit. For the DC two-wire case it additionally answers the three reverse questions: maximum length, maximum current and minimum cross-section.

For AC the drop is ΔU = 2 (or √3) · I · L · (R′ · cos φ + X′ · sin φ), so the reactance term is mandatory. It is found in the cable datasheet, not in the standard, and varies by more than a factor of two depending on construction. Assuming a typical value would be exactly the kind of silent guess this engine refuses to make.

No — this calculator checks voltage drop only. A cross-section can meet the drop limit and still be thermally impermissible; ampacity is a separate check, which the result explicitly flags. Harmonics, contact resistance at terminals and connectors, short-circuit withstand and skin effect at very large cross-sections are also outside the scope.

The direction: the wire-size calculator recommends a size for given requirements; this one checks an EXISTING or planned run — and additionally answers the three reverse questions: how much longer may the run get at this cross-section, how much current does it carry, what cross-section would be minimal? That is the question you actually have on site with the cable drum in hand.

Your design limit (e.g. 3%) is a quality decision — for module-controller runs 1–2% often pays, since every point directly costs yield. The code limit is binding independently. The calculator shows both lines in the bar and warns separately: breaching your limit means inefficient, breaching the code limit means impermissible.

Copper resistance rises ~0.4% per kelvin: between a 20 °C workshop measurement and 60 °C in a sun-exposed cable duct lie 16% more resistance — and thus 16% more voltage drop. The calculator corrects resistance to your conductor temperature; the 30 °C default is conservative indoors, too low for roof runs in summer.

Yes — since 5 August 2026 through the interface too: single-phase (230 V) and three-phase (400 V), with power factor and reactance. The AC half previously existed only in the calculation core; the form had no switch for it. For three-phase the formula uses √3 instead of factor 2 — 16 A over 25 m in 2.5 mm² gives 1.24 %.

From the NYY catalogue dataset for the chosen cross-section — sourced, not guessed, and named as a note. The engine itself deliberately refuses to guess it: it lives in the cable datasheet, not the standard, and varies by construction by more than a factor of two. If you have your datasheet, enter the value via the switch — it then wins.

Because that is exactly the calculator's question: “I have 6 mm² lying around — is that enough?” For 30 A over 5 m at 12 V the answer is no — 7.47 % against the permitted 3 %. An example that always “passes” would hide the calculator's warning side. The three reverse questions beside it show the ways out: shorter run, less current, or 16 mm².

They solve the same equation for one variable each: how long may the run be at most? How much current does it take within the limit? What cross-section would be needed? For the DC two-wire case all three solve in closed form; in the AC case with reactance they are omitted, because the equation no longer solves for a single variable — the page says so openly.

Loss power times operating hours times electricity price — both factors are adjustable since 5 August 2026. The 6 mm² example burns 27 W; at 1,000 operating hours and 31.1 ct that is about €8 a year, a continuous runner would exceed €70. Set against the extra cost of 16 mm², the thicker cable often pays for itself in the first year.