Earth Conductor Size Table Jun 2026

Selecting the right earth conductor size is one of the most critical steps in electrical design. It ensures that in the event of a fault, the protective device (like a circuit breaker) trips fast enough to prevent electric shock or fire.

In some cases, using the table sizes is uneconomical or impractical, particularly for very large cables or specific fault current durations. Engineers may calculate a smaller earth size using the (found in IEC 60364-5-54): earth conductor size table

Where:

Keep in mind that this is a highly simplified example and actual tables may be more comprehensive and complex. Selecting the right earth conductor size is one

When reviewing an earth conductor size table, ensure that it aligns with the relevant safety standards and considers the specific requirements of your electrical installation. If you're unsure, consult with a qualified electrician or electrical engineer. Engineers may calculate a smaller earth size using

S=I2tkcap S equals the fraction with numerator the square root of cap I squared t end-root and denominator k end-fraction Cross-sectional area ( mm2m m squared I: Fault current (Amperes) t: Operating time of the protection device (Seconds)

| Phase Conductor Size (mm²) | Min. Earth Conductor Size (mm²) – Copper | Notes | |---------------------------|-------------------------------------------|-------| | ≤ 16 | Same as phase conductor | Example: 10 mm² phase → 10 mm² earth | | 25 – 35 | 16 | – | | 50 – 95 | 25 | – | | 120 – 150 | 35 | – | | 185 – 240 | 50 | – | | 300 | 70 | – |