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Single-core in conduits or trunking on wall surface, in wall or in floor. Better heat exchange than methods A. Reference ambient temperature: 30 °C.
Professional calculator for selecting the minimum cable cross-section meeting three normative requirements simultaneously: long-term current carrying capacity per N-SEP-E-002, permissible voltage drop per PN-HD 60364-5-52, and minimum mechanical cross-section. The calculator automatically corrects current capacity with temperature (k₁) and grouping (k₂) correction factors.
Tool for electrical designers, electricians, and engineers. Supports 7 installation methods (A1, A2, B1, B2, C, E, F), copper and aluminium conductors with PVC or XLPE insulation, single-phase and three-phase circuits. The result is the selected cross-section with a comparison table of three nearest sizes — with full indication of which criterion is decisive. Results can be saved to a project.
Set installation parameters: circuit type (single-phase/three-phase), material (Cu/Al), insulation (PVC/XLPE), installation method (A1–F) and number of loaded conductors. The calculator automatically retrieves the appropriate current capacity data from N-SEP-E-002 tables.
Enter the load: power [kW] or current [A], route length [m], cos φ, ambient temperature and number of circuits in the bundle. The calculator computes correction factors k₁ and k₂ and adjusts the current capacity. Select supply source and circuit purpose (lighting/other) to establish the voltage drop limit.
Read the result: the calculator indicates the minimum cross-section meeting all requirements. The comparison table shows 3 nearest cross-sections with their current capacity, voltage drop and margin. The 'decisive criterion' label indicates whether current capacity or voltage drop determined the selection.
Based on the given parameters, the program determines a complete set of data for designing an electrical circuit:
Single-phase (230 V) or three-phase (400 V). Affects current calculation from power and the voltage drop formula. Three-phase circuits are used for loads above 3.7 kW (motors, electric cookers).
Copper (Cu) — higher current capacity and conductivity, standard in domestic installations. Aluminium (Al) — cheaper, lighter, but requires larger cross-sections; used in supply lines from 16 mm² upward. N-SEP-E-002 provides separate capacity tables for both materials.
Installation method determines heat dissipation and current capacity: A1/A2 — in conduits in walls (poorest cooling), B1/B2 — in cable trays, C — directly on wall, E — on cable ladders (good cooling), F — on cleats (best capacity). The method choice can change the required cross-section by 1–2 steps.
Active power or design current — values convert automatically accounting for cos φ. Typical powers: 16A socket circuit ≈ 3.7 kW, electric cooker ≈ 7 kW, heat pump ≈ 4–8 kW. For multiple loads, sum powers with the simultaneity factor applied.
One-way cable route length. Affects voltage drop — for short routes (<15 m) current capacity determines sizing, for long routes (>30 m) voltage drop increasingly forces a larger cross-section.
Ratio of active to apparent power. Default: 0.85. Lower cos φ means higher current for the same power and a thicker required cable. Typical values: heaters = 1.0, LED = 0.95, air conditioning = 0.85, motors = 0.80.
Ambient temperature affects factor k₁: at 40 °C capacity drops by ~13% (PVC) or ~9% (XLPE). Number of circuits in a bundle affects factor k₂: 3 circuits in one conduit reduce capacity by ~30%. Both factors multiply the base capacity from the table.
Determines permissible voltage drop: public network + lighting = 3%, public network + other = 5%, private source + lighting = 6%, private source + other = 8%. For long routes, the voltage drop limit often forces a larger cross-section than current capacity alone.
Always check both criteria simultaneously — current carrying capacity and voltage drop. For short domestic circuits (up to 20 m), capacity is decisive, but for longer routes (main supply lines, garage circuits, outdoor lighting), voltage drop often forces a cross-section 1–2 steps larger. The grouping factor k₂ can dramatically reduce capacity — 6 circuits in one conduit means ~43% reduction. In such cases, consider running circuits on separate routes. Remember that cable sizing is not everything — you must also select appropriate overcurrent protection meeting the condition I_B ≤ I_n ≤ I_z. Do not use Al below 16 mm² — the standard does not provide capacity values for smaller aluminium cross-sections.
The cross-section is chosen so that it simultaneously satisfies three conditions per N-SEP-E-002: long-term current-carrying capacity (I_B ≤ I_z after correction by factors k₁ and k₂), permissible voltage drop (ΔU% ≤ limit per PN-HD 60364-5-52), and the minimum mechanical cross-section. The most demanding condition governs — the calculator checks all three at once and shows which one is decisive.
In typical residential installations, 1.5 mm² Cu is used for lighting circuits (10 A protection) and 2.5 mm² Cu for general socket circuits (16 A). Dedicated circuits such as an electric cooker or water heater often need 4–6 mm². These are guideline values — for longer runs or higher loads the cross-section should be recalculated against voltage drop and current-carrying capacity.
They are factors that correct a conductor's current-carrying capacity. k₁ accounts for an ambient temperature different from the reference (30 °C in air, 20 °C in the ground), and k₂ accounts for the mutual heating of conductors grouped together or sharing a route. The corrected capacity is I_z = I_z(tab) × k₁ × k₂; the more adjacent circuits and the higher the temperature, the lower the permissible capacity.
Copper has higher capacity and conductivity, so a smaller cross-section suffices for the same current; it is the standard in residential installations. Aluminium is cheaper and lighter, and economical for larger cross-sections (≥ 16 mm²) in supply lines and service cables. For the same current, aluminium requires a larger cross-section and appropriate terminals.
It depends on the length of the run. For short circuits, current-carrying capacity (linked to protective-device selection) usually governs, while for long lines it is the voltage-drop condition that forces a larger cross-section than the current alone would. Both criteria must therefore be checked at once; the calculator indicates which one is decisive.
The reference methods per PN-HD 60364-5-52 describe how the conductor is routed, which affects heat dissipation and therefore current-carrying capacity: A1/A2 — in conduits in an insulated wall, B1/B2 — in trunking and cable channels, C — directly on a wall, E/F — on ladders and brackets in air, D — in the ground. Routing with better cooling (E, F, in the ground) allows a higher capacity for the same cross-section.
Usually yes. For Cu/PVC with 2 loaded conductors, the ampacity Iz of 2.5 mm² is: A1 19.5 A, A2 18.5 A, B1 24 A, B2 23 A, C 27 A — each ≥ 16 A, and I₂ = 1.45·16 = 23.2 A ≤ 1.45·Iz. The condition only fails after the grouping correction: with method A1 and 2 circuits in one conduit, Iz = 19.5·0.8 = 15.6 A < 16 A — then you need 4 mm² or a B13 breaker. In the calculator pick “Protective device In = 16 A” as the current basis, and in the protection calculator compute Iz from the installation method, number of grouped circuits and temperature.
Cable sizing is one of the key stages in electrical installation design. For a complete project, you may also find useful:
Detailed step-by-step guide: how to calculate load current, select installation method, apply correction factors k₁ and k₂, check voltage drop, compare copper vs aluminium — with a complete worked example for a 7 kW cooker:
Electrical cable sizing — step-by-step guide per N-SEP-E-002Designing a cable line? Build the route's longitudinal profile and a CAD-ready DXF.
Paste the route coordinates — Altivo builds the longitudinal profile with elevations, and the DXF export drops straight into AutoCAD. No install, no dongle, in the browser.
