Calculate cross-section and voltage drop
Enter your circuit data—the result is calculated on the fly. The starting fields contain sample values; replace them with your installation data.
Complete the data on the left to see the result.
A reference tool for preliminary selection. The calculator calculates voltage drop only, using the formulas shown below. The final cross-section selection—including long-term current carrying capacity, installation method, ambient temperature, and protection—is performed by the designer or installation company in accordance with the design documentation and applicable regulations.
How We Count - Formulas and Constants
The calculator doesn't use any hidden factors. Below is a complete set of formulas and values used by the website's code.
Voltage Drop - DC and AC 1-Phase
ΔU = (2 · ρ · L · I) / S
Mnożnik 2 takes into account the current path back and forth (two circuit wires) with the length of the route L given in one direction.
Voltage Drop - AC 3 Phase
ΔU = (√3 · ρ · L · I · cosφ) / S
For a symmetrically loaded 3-phase system, instead of the multiplier 2 apply √3 ≈ 1,73, and the formula includes the power factor cosφ (in the calculator by default 1,0).
Resistivity ρ
Copper: ρ = 0,0175 Ω·mm²/m aluminum: ρ = 0,028 Ω·mm²/mBoth are textbook values for temperature 20 °C — at higher temperatures the resistance of the wire is greater, which this calculator does not take into account.
Type series of cross-sections
We round the result up to the standard commercial series of core cross-sections: 1,5 / 2,5 / 4 / 6 / 10 / 16 / 25 / 35 / 50 / 70 / 95 mm²Designations in formulas: ΔU — voltage drop [V], L — one-way route length [m], I - current [A], S — cross-section of the vein [mm²].
How to choose input data
The following guidelines are design practice—we'll state it explicitly. Always use calculation values from your project documentation and device data sheets.
Electricity - DC page
In design practice, the short circuit current of the module is often assumed to be the design current of the string. Isc (from the catalog card) multiplied by 1,25 — Allowance for solar radiation conditions above STC. This is a design practice, not a requirement of this calculator.
Electricity - AC page
For an AC circuit, the starting point is usually the inverter's maximum output current, as listed in its datasheet. For three-phase systems, enter the current for one phase.
Operating voltage
On the DC side, this is the operating voltage of the string at the operating point (dependent on the number of modules) - default 600 V is just an example for editing. On the AC side: 230 V (1-phase) or 400 V (3-phase).
Voltage drop limit
The calculator doesn't impose a limit - you choose 1%, 2% or 3%The voltage drop limit for a specific circuit is determined by the installation design. A smaller voltage drop also means less energy loss throughout the installation's operating life.
Frequently asked questions about PV cable cross-section
What is the difference in selecting the cross-section for the DC side and the AC side?
The physics are the same—we calculate the voltage drop across the resistance of the wires—but the input data and the formula differ. On the DC side, the current and voltage result from the string configuration, and the formula uses a multiplier. 2 (two wires). A single-phase AC circuit is calculated using the same formula with a voltage 230 V; for a symmetrical 3-phase circuit the multiplier is √3 and the power factor comes in cosφFor the same current and same path, a lower circuit voltage means a larger percentage drop.
Why do I provide a one-way route when the formula uses ×2?
Current flows to the receiver through one wire and returns through the other—the circuit resistance is the sum of the resistances of both wires. Therefore, the formula uses twice the path length: you enter the one-way distance. L, and the multiplier 2 (or √3 for a symmetrical 3-phase system) is already in the formula.
What to do if the result falls between the cross-sections of the type series?
The calculated cross-section almost never accurately matches the commercial value. In such cases, the next larger cross-section in the series is selected, and that's what the calculator recommends. The results table also shows the next smaller and larger cross-sections, along with their voltage drops, so you can assess the margin.
Does the calculator replace the installation design?
No. This is a preliminary selection tool only—it calculates voltage drop using the formulas shown above. It does not check long-term current carrying capacity, installation method, ambient temperature, or fuse selection. The final cross-section selection is made by the designer or installation company in accordance with the design documentation and applicable regulations.
Select cabling and protection for your project
At the wholesaler PVGroup.pl You'll find accessories, cabling, and protection for PV installations, and practical technical solutions in our knowledge base. If you need help choosing, please contact us.