Cable cross-section calculator for solar installations (DC and AC)

Calculate the minimum cable cross-section Copper cable for the section between the panels and the regulator, the battery and the inverter, or the inverter and the control box, depending on the current, length and voltage drop it can handle. It returns the standard cross-section, the actual voltage drop, the approximate maximum current and the recommended fuse.

Section details

How is it calculated?

The cross-sectional area due to voltage drop is S = 2 · L · I · ρ / ΔV in continuous, single-phase (forward and return) mode and S = √3 · L · I · ρ / ΔV in three-phase, where ρ is the resistivity of copper at operating temperature. The next higher standardised cross-section is then selected, and it is verified that the cable’s permissible current exceeds the design current. In photovoltaic systems, the current from the panels is increased by 25 % (as irradiance may exceed 1000 W/m²).

Rule Victron for battery cables

For the battery–inverter/charger section of up to 5 m, Victron applies a simple rule: the maximum permissible current is twice the cross-sectional area in mm² (35 mm² → 70 A, 50 mm² → 100 A, 70 mm² → 140 A, 95 mm² → 190 A). This is based on the inverter’s rated current (power in VA ÷ battery voltage), without the 1.25 photovoltaic factor, and corresponds to the table in the MultiPlus-II manual: 48/3000 → 35 mm², 48/5000 → 70 mm², 48/8000 → 2×50 mm², 48/15000 → 2×95 mm². The calculator automatically applies this to DC circuits of up to 5 m and selects the larger of the two cross-sections (Victron rule or voltage drop). At 12 V and high power levels, the voltage drop takes precedence, not the rule. The fuse must be as specified in the equipment manual (≈ 2.9 A per mm² of cable).

Typical values

• 48 V / 5000 W battery-inverter at 2 m: 35–50 mm² with a voltage drop of 1 %.
• 12 V / 3000 W battery-inverter at 1.5 m: 70–95 mm². At 12 V, the cables are enormous: that is why large systems operate at 24 or 48 V.
• String of panels (10 A, 600 V) at 30 m: 4–6 mm² of H1Z2Z2-K solar cable.
• 5 kW single-phase inverter connected to the distribution board at a distance of 15 m: 6 mm² (voltage drop ≈1 %).

For the battery cable cross-section in Victron units, please also refer to the table of recommended cross-sections in the manual for each MultiPlus unit, and read how to calculate the cross-sectional area of a cable.