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Earthing System Design Calculator

AS/NZS 3000:2018 Section 5 (Australian & New Zealand)

◆ Phase 3 Calculator

Inputs

Typical range: 10–10000 Ω·m (measured on-site)

Depth for rod; length for strip/plate/ring

Center depth (typically 1–3 m)

▶Electrical parameters

Prospective earth fault current (from distribution)

Protective device disconnection time (typ. 0.1–0.4 s)

Results

Earth Resistance

77.87

Ω

❌

Touch voltage limit (≤50V typical)

38934.79990323499 V (<= 50)

❌

Earth resistance limit (TN-C-S)

77.86959980646998 Ω (<= 10)

❌

Step voltage limit

20000 V (<= 75)

✅

Earth conductor size (adequate)

4 mm² (>= 4)

Single Electrode Resistance81.968 Ω
Grid Resistance (parallel)81.968 Ω
Practical Resistance77.870 Ω
Touch Voltage (Prospective)38934.8 V
Touch Voltage Limit50 V
Step Voltage20000.0 V
Step Voltage Limit75 V
Min Earth Conductor4 mm²

Touch voltage approaching limit: 38934.8V (limit: 50V)

Earth resistance approaching limit: 77.87Ω (limit: 10Ω)

Important: These results are indicative only. Earthing system design must be verified by a qualified electrical engineer in accordance with AS/NZS 3000:2018 Section 5. Earth resistance testing must be performed on-site with appropriate instrumentation.

Earthing System Design Guide — AS/NZS 3000:2018 Section 5

A properly designed earthing system protects persons and equipment from electric shock and overvoltage. This calculator determines earth electrode resistance, touch voltage, step voltage, and conductor sizing for compliance with AS/NZS 3000:2018.

Earthing System Types

  • TN-S: Separate neutral and earth conductors from supply. Common in Australia for single-phase domestic installations.
  • TN-C-S: Combined neutral-earth (PEN) from supply, split at installation boundary. Three-phase networks in Australia (TNCS = >Earthing at MEN link).
  • TT: Independent earth electrode at installation (no connection to supply earth). Used in remote areas and some rural installations.
  • IT: Floating neutral (isolated or impedance-grounded). Specialized high-continuity systems (industrial, medical, data centres).

Electrode Types & Soil Conditions

  • Rod electrode: Vertical driven rod (typically 16mm diameter, 1.5–3m length). Most common in Australia; cost-effective.
  • Strip electrode: Horizontal copper tape (typically 50mm width). Good for shallow installations or where vertical boring difficult.
  • Plate electrode: Buried copper plate (0.5–2 m²). Lower resistance in high-resistivity soil; used when space permits.
  • Ring electrode: Loop of conductor around building perimeter. Provides redundancy and lower resistance than single electrode.

Soil Resistivity Impact

  • Clay: >20–100 Ω·m (low resistivity); good earthing, rod 1–1.5m often sufficient
  • Loam: 50–500 Ω·m (moderate); typical for mixed soil; rod 1.5–2m usually adequate
  • Sand: 100–2000 Ω·m (high); requires longer rod (2–3m) or multiple electrodes
  • Rock/Gravel: 1000–10000 Ω·m (very high); parallel electrodes, strip, or plate recommended

Compliance Limits (AS/NZS 3000:2018)

  • Touch voltage: Maximum 50V AC (normal locations), 25V (special locations like bathrooms) — Section 5.3.2.2
  • Step voltage: Maximum ~80–100V depending on clearance time — Section 5.3.2.3
  • Earth resistance: TN systems >≤ 10Ω typical; TT system target >≤ 10Ω (higher permissible with supplementary measures) — Section 5.4.5
  • Conductor sizing: Based on adiabatic equation (S = √(I² × t) / k) where I = fault current, t = clearance time — Appendix A

Disclaimer: These results are indicative only. Earthing system design must be verified by a qualified electrical engineer in accordance with AS/NZS 3000:2018 Section 5 and site-specific soil measurements. Earth resistance testing must be performed on-site with appropriate instrumentation (earth resistance tester). This guide does not replace professional electrical design and testing.