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Professional calculator for computing voltage drop in low-voltage electrical circuits. Calculations comply with PN-HD 60364-5-52 (Table G.52.1) — accounting for conductor conductivity at operating insulation temperature, power factor cos φ, and for large cross-sections (above 50 mm² Cu / 70 mm² Al) cable reactance.
Tool for electrical installation designers, licensed electricians, and inspectors. The calculator supports single-phase (230 V) and three-phase (400 V) circuits, copper and aluminium conductors with PVC (70 °C) or XLPE (90 °C) insulation. Results include voltage drop in volts and percent, end-of-line voltage, and compliance assessment against normative limits.
Set cable parameters: circuit type (single-phase / three-phase), material (Cu / Al), insulation (PVC / XLPE) and cross-section from the standard range (1.5–240 mm²). The calculator automatically selects the conductivity γ for the chosen material/insulation combination.
Enter load and conditions: cable length [m], power [kW] or current [A] (the other value converts automatically), and power factor cos φ. Select the supply source (public network / private) and circuit purpose (lighting / other) — this determines the permissible voltage drop limit.
Read the result: the calculator displays ΔU in percent and volts, design current I_B, end-of-line voltage U_end, and whether the drop is within the permissible limit (3% / 5% / 6% / 8% depending on source and purpose). The result background colour (green/red) instantly indicates compliance.
Based on the given parameters, the calculator determines:
Single-phase (230 V, 2 live conductors) or three-phase (400 V, 3 live conductors). The choice affects the calculation formula: coefficient b = 2 for single-phase, b = √3 for three-phase.
Copper (Cu) — conductivity γ = 44.4 m/(Ω·mm²) with PVC, 42.4 with XLPE. Aluminium (Al) — γ = 27.5 with PVC, 26.3 with XLPE. Copper gives lower voltage drop for the same cross-section but is more expensive. New domestic installations use copper exclusively; aluminium is used in supply lines and cables ≥ 16 mm².
Conductor cross-section from the standard range: 1.5 — 2.5 — 4 — 6 — 10 — 16 — 25 — 35 — 50 — 70 — 95 — 120 — 150 — 185 — 240 mm². If you don't know the cross-section yet — use the cable sizing calculator, which automatically selects the minimum cross-section meeting both current capacity and voltage drop requirements.
Cable route length measured one way — from the distribution board (or supply source) to the load. Voltage drop increases linearly with length. For routes exceeding 100 m, the standard permits increasing the limit by 0.005% per additional metre (max +0.5%).
Active power of the load in kW or design current in A — values convert automatically accounting for cos φ and nominal voltage. For multiple loads, enter the total power with the simultaneity factor applied.
Ratio of active to apparent power. Default: 0.85 (typical mixed load). Typical values: heaters, incandescent = 1.0; LED = 0.95; air conditioning = 0.85; motors = 0.80; welding machines = 0.35–0.50. Lower cos φ means higher current for the same power, hence greater voltage drop.
Source: Type A (public network) or Type B (private source — generator, UPS). Purpose: lighting or other. The combination determines the permissible drop per PN-HD 60364-5-52: Type A + lighting = 3%, Type A + other = 5%, Type B + lighting = 6%, Type B + other = 8%.
Voltage drops across individual installation sections add up cumulatively — if the main supply line has 2% and the final circuit has 2.5%, the total drop is 4.5% and must stay within the limit. For long routes (>30 m) and high currents, voltage drop often forces a larger cross-section than current capacity alone requires. For LED lighting circuits, even a modest drop (>3%) can cause visible flicker. In DC photovoltaic installations, due to lower nominal voltage, the recommended drop is only 1% (design recommendation, not a normative limit). During motor starting (current 5–8× rated), momentary voltage drop can reach double digits — check whether it affects other loads on the circuit.
Per PN-HD 60364-5-52 (table G.52.1), the permissible voltage drop from the origin to the load is 3% for lighting circuits and 5% for other circuits when supplied from the public network (Type A), and 6% and 8% respectively when supplied from a private source such as a generator (Type B). The limit applies to the sum of drops across all sections — from the supply main to the final circuit.
For typical cross-sections (with reactance neglected) the formula is ΔU% = (b × I × cos φ × L × 100) / (γ × S × U₀), where b = 2 for a single-phase circuit and b = √3 for three-phase, cos φ is the load power factor, γ is conductivity at the insulation's operating temperature, S is the cross-section in mm², L is the length in metres, and U₀ is the nominal voltage. For cross-sections above 50 mm² Cu / 70 mm² Al you must also account for conductor reactance (the full formula with the R·cos φ + X·sin φ term). The calculator selects the correct formula automatically.
Too low a voltage at the end of the line causes loads to malfunction: motors lose torque and overheat (they need at least 90% of nominal voltage), LED lighting flickers, and electronic devices may reset. Prolonged undervoltage shortens equipment lifespan and increases energy losses in the conductors.
The most effective way is to increase the conductor cross-section, since the drop is inversely proportional to it. Shortening the run, using copper instead of aluminium, splitting the load across several circuits, or switching to a three-phase supply also help. On very long lines, supply at a higher voltage with transformation closer to the load is sometimes used.
No. On long runs with high currents it is the voltage-drop condition, not the current-carrying capacity, that forces a larger cross-section. The cross-section must therefore be checked against both criteria at once — which is exactly what the cable cross-section calculator does.
For the DC circuits on the PV generator side, a design voltage drop of ≤ 1% is recommended, well below the limits for AC installations. At the low DC voltage, percentage losses quickly reduce the energy yield. This is a design recommendation, not a regulatory limit.
Voltage drop is one of the criteria in electrical installation design. For a complete project, you may also find useful:
Article explaining voltage drop formulas (single-phase and three-phase), permissible values per standards, conductivity tables, cascading drops, PV installations, and a practical step-by-step calculation example:
Voltage drop in electrical installations — how to calculate and when it matters