Cable Current-Carrying Capacity and Sizing Guide (IEC 60364-5-52)
Reference ampacity tables for copper PVC (70 °C) and XLPE (90 °C) cables under IEC / TS HD 60364-5-52 installation methods, voltage drop formulas, and breaker coordination.
Cable current-carrying capacity (Iz) is the maximum continuous RMS current a conductor can carry without exceeding the thermal limit of its insulation. Under IEC / TS HD 60364-5-52, the same copper cross-section carries substantially different current depending on insulation compound (PVC 70 °C vs XLPE 90 °C), installation method (conduit, perforated tray, buried), and ambient temperature.
> Related Category: Compare technical specifications and model options directly in the Cables, NYY Cables, and N2XH Cables categories.
Why PVC (70 °C) and XLPE (90 °C) limits change ampacity
Current flowing through copper generates I²R losses. At reference ambient conditions (30 °C in air, 20 °C in ground), maximum permissible conductor temperature depends on insulation material:
- PVC-insulated cables (NYA, TTR, NYY): 70 °C continuous operation and 160 °C for 5 s short-circuit (up to 300 mm²).
- XLPE halogen-free cables (N2XH): Cross-linked polyethylene core insulation allows 90 °C continuous operation and 250 °C during a 5 s short circuit, yielding roughly 18%–25% higher ampacity for the same cross-section (see What is XLPE cable?).
IEC 60364-5-52 reference ampacity table (Copper conductors)
Typical reference values at 30 °C air / 20 °C soil for a single circuit:
- Method B1: Single-core cables in conduit in wall (2 loaded conductors, single-phase).
- Method C: Multi-core cable clipped direct or on perforated tray (3 loaded conductors, three-phase).
- Method D2: Multi-core cable buried direct in ground (3 loaded conductors, soil thermal resistivity 1.0 K·m/W).
| Size (mm²) | B1: PVC 2-cond. (A) | C: PVC 3-cond. NYY (A) | C: XLPE 3-cond. N2XH (A) | D2: Buried PVC NYY (A) |
|---|---|---|---|---|
| 1.5 mm² | 17.5 | 17.5 | 23 | 22 |
| 2.5 mm² | 24 | 24 | 31 | 29 |
| 4 mm² | 32 | 32 | 42 | 38 |
| 6 mm² | 41 | 41 | 54 | 47 |
| 10 mm² | 57 | 57 | 75 | 63 |
| 16 mm² | 76 | 76 | 100 | 81 |
| 25 mm² | 101 | 96 | 127 | 104 |
| 35 mm² | 125 | 119 | 158 | 125 |
| 50 mm² | 151 | 144 | 192 | 148 |
| 70 mm² | 192 | 184 | 246 | 183 |
Derating factors, voltage drop, and breaker coordination
Site ampacity is adjusted as Iz = Iz0 × k1 × k2 (e.g., at 40 °C ambient, `k1 ≈ 0.87` for PVC and `0.91` for XLPE; 3 touching multi-core circuits on a tray apply `k2 ≈ 0.79–0.82`). On long feeders, verify voltage drop (κ ≈ 56 m/(Ω·mm²) for copper):
- Single-phase (230 V): `ΔU% = (200 × L × I × cos φ) / (56 × S × 230)`
- Three-phase (400 V): `ΔU% = (100 × √3 × L × I × cos φ) / (56 × S × 400)`
Finally, enforce IEC 60364-4-43 overload coordination (`Ib ≤ In ≤ Iz`) alongside miniature circuit breaker sizing so the protective device rating In never exceeds derated cable ampacity Iz.
Frequently asked questions
How many amps can a 2.5 mm² copper cable carry?
In conduit (Method B1 at 30 °C), a 2.5 mm² PVC-insulated copper conductor has a reference ampacity of 24 A and is typically protected by a 16 A (or up to 20 A when derated conditions permit) circuit breaker.
Why does N2XH carry more current than NYY of the same size?
N2XH uses XLPE insulation rated for 90 °C continuous conductor temperature, whereas NYY uses PVC rated for 70 °C. Verify that switchgear terminals are rated for higher conductor temperatures before utilizing full 90 °C ampacity.
Is ampacity alone sufficient to size a feeder cable?
No. Feeders exceeding 30–40 m frequently require one or two cross-section steps larger to keep voltage drop within 3% (lighting) or 5% (power/motors) and to satisfy fault loop disconnection times.