PV DC cable

PV direct-current circuits use cables made for photovoltaic systems. DBN V.2.5-23:2025 lists DSTU EN 50618:2018, the standard for such cables (typically marked H1Z2Z2-K). They withstand UV and the high temperature under the panels.

Three conditions decide the section. First, temperature: for cables heated directly from the underside of the modules, DSTU HD 60364-7-712:2022 (cl. 712.523.101) requires an ambient temperature of at least 70 °C. Second, current: with one or two strings in parallel the cable rating I_z must be at least the string’s I_{SC MAX} (cl. 712.433.101). Third, voltage drop.

Copper resistance at 70 °C is about 20 % higher than at 20 °C: ρ₇₀ = 0.0175·(1 + 0.00393·50) ≈ 0.0209 Ω·mm²/m. We found no voltage-drop limit for PV DC circuits in the norms we hold, so the 1.5 % in Solispec is an app target, not a requirement.

A few practical points. Fix the cable under the panels so that it neither lies on the roof nor sags. Run the plus and minus of a string side by side to keep the loop area small, since a nearby lightning strike induces surges in that loop. Over a combustible roof the cable runs in metal trays or conduit. For long runs on a ground plant, compute the voltage drop for 6 and 10 mm² and weigh the cost of copper against the yearly energy loss. The section required by current stays the lower bound, and it may not be reduced to save money.

The Solispec engine picks 4, 6 or 10 mm² for a 1.5 % voltage drop with resistance at 70 °C, then checks the current. It takes the rating I_z from the maker’s H1Z2Z2-K datasheet (two cables side by side on a surface) with a 0.91 factor for 70 °C; we did not obtain the text of the standard’s annex, so the engine says plainly that this is datasheet data. If I_z is below the cable current, the section goes up to 16 mm². Parallel strings on one MPPT input are treated as joined before a common cable that carries their sum.

Solispec constructor