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Earth fault resistance

Maximum Rphe and Re to compare with continuity tests.

Table 8.2 derivation for copper final subcircuits: Rphe is 64% of the Table 8.1 maximum Zs and Re is its earth-conductor share. Compare with continuity resistances measured near 20 °C.

Cross-sectional area of the active conductor.

Cross-sectional area of the protective earthing conductor.

Rated current of the overcurrent protective device.

Circuit-breaker type or fuse. Sets the Table 8.1 maximum Zs.

Clause 5.7.2. Table 8.1 gives 5 s values for fuses only.

Results

Complete the form and calculate to see the maximum Rphe and Re.

Method and assumptions

  • As in the notes to AS/NZS 3000:2018 Table 8.2, Rphe is 64% of the Table 8.1 maximum Zs: 80% of Zs is allowed for the final subcircuit, and a further 80% because test readings are taken with conductors near 20 °C rather than at operating temperature.
  • Re is the earth conductor's share of Rphe for copper conductors: Re = Rphe × Sph ÷ (Sph + Spe). For the combinations listed in Table 8.2 this reproduces its values.
  • Measured Rphe is compared with this limit under Clause 8.3.9.3(b); Re may be used when testing continuity of the earthing system (Clause 8.3.5).

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Check the stated method and limits against your installation. Results are calculation aids, not certification.

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Calculation model 2026-11-02.1