WireTheSunCommon cable sizesCable size for 125 A over 20 m, three-phase
For 125 A over 20 m on a 400 V three-phase supply, use at least 70 mm² (2/0 AWG) copper cable, protected by a 160 A breaker. Voltage drop: 0.3%.
Assumes copper cable clipped to a wall (or flexible battery cable for DC), 30 °C, PVC insulation. Change anything below.
- 70 mm²
- 2/0 AWG
- 160 A
- Breaker
- 0.3%
- Voltage drop
- 22 m
- 5-core cable
How the cable runs
Use at least70 mm²2/0 AWG
Breaker160 A
Voltage drop0.3% · 1.39 V
Current125 A
Cable carries up to184 A
Heat decides this size: it carries the breaker current without overheating, and the voltage drop is fine.
Cores
5 cores: L1, L2, L3, neutral and earth (4 cores if no neutral is needed)
Which cable
NYM-J / XVB / 5-core LSZH
Fixed wiring clipped to walls indoors.
H07RN-F (rubber, flexible)
Machines, workshops and anything that moves or vibrates.
- Several circuits bundled together carry less each: allow for grouping (IEC 60364-5-52 Table B.52.17).
- Check the earth fault loop impedance and the RCD protection required by your local rules.
Guidance based on IEC 60364-5-52 for copper cables. Always check against your local rules (BS 7671, NEC, NF C 15-100, RTIEBT…) and the cable maker’s data.