WireTheSunCommon cable sizes

Cable size for 16 A over 20 m, three-phase

For 16 A over 20 m on a 400 V three-phase supply, use at least 2.5 mm² (14 AWG) copper cable, protected by a 20 A breaker. Voltage drop: 1.2%.

Assumes copper cable clipped to a wall (or flexible battery cable for DC), 30 °C, PVC insulation. Change anything below.

The same current over other distances

DistanceCable sizeVoltage drop
10 m2.5 mm² (14 AWG)0.6%
20 m2.5 mm² (14 AWG)1.2%
30 m2.5 mm² (14 AWG)1.9%
50 m2.5 mm² (14 AWG)3.1%
100 m4 mm² (12 AWG)3.9%
2.5 mm²
14 AWG
20 A
Breaker
1.2%
Voltage drop
22 m
5-core cable
How the cable runs
Use at least2.5 mm²14 AWG
Breaker20 A
Voltage drop1.2% · 4.99 V
Current16 A
Cable carries up to24 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.

Planning a whole solar system?Describe it and we size every cable, fuse and part, with a wiring diagram.