DC String Voltage Drop and Cross-Section Sizer

Voltage drop on the direct-current side is decided by string current, one-way run length and conductor area, and it is the number that most often forces a cross-section change after a layout is drawn. Enter your run and this calculator returns the drop in volts and percent, then names the smallest cross-section in our certified series that meets your target.

String current, A

One-way length, m

Cross-section, mm²

System voltage, V

Target drop, %

—Voltage drop, percent of system voltage

—Voltage drop, volts over the loop

—Smallest certified cross-section meeting your target, mm²

Enter a run and press calculate. Nothing is sent anywhere; the arithmetic happens in your browser.

The same run across the certified series

Bars are scaled against your target. Green means the cross-section meets it on this run.

What this model assumes

Conductor resistivity is taken from our own published figure, a maximum conductor resistance of 5.09 Ω/km at 20 °C on a 4 mm² Class 5 tin-plated copper conductor, which works out at 0.02036 Ω·mm²/m.
Using a published maximum rather than a nominal value makes the answer conservative: a real conductor will normally drop slightly less than this.
Resistance is taken at 20 °C. A hot conductor has higher resistance, so a run close to your limit at 20 °C will exceed it in service.
The length you enter is one way. The calculation doubles it, because the current returns.
This is a resistance calculation only. It is not an ampacity check and it does not tell you whether the cross-section can carry the current safely.

Send your run length and current with an enquiry

Our certified cross-section range on the H1Z2Z2-K line is 1.5 to 240 mm². Ampacity, grouping and installation-method corrections belong with your installation designer, not with a cable supplier’s web page.