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Maximum Earth Fault Loop Length by Protective Device

Convert a required fault current into a maximum loop impedance and route length using entered source and conductor data.

Inputs

Project inputs and assumptions

Range: 1–100,000 V

Enter the line-to-earth voltage.

Range: 0.01–100,000,000 A

Enter the current required by the selected protective-device basis.

Range: 0–100,000 Ω

Enter measured or verified source-side loop impedance.

Range: 0–100,000 Ω/km

Enter the line conductor resistance.

Range: 0–100,000 Ω/km

Enter the protective-earth conductor resistance.

Range: 0–100,000 m

Enter the proposed one-way route length.

Result

Proposed-route fault current (A)
533.4
Proposed-route loop impedance (Ω)
0.4312
Route-length margin (m)
3.5
Maximum one-way route length (m)
43.5
Maximum permitted loop impedance (Ω)
0.4600

Formula

Calculation logic

Formula definitions and substituted values.

Before relying on the result

  • Solve maximum route length from a target fault current
  • Compare a proposed route against the available EFLI margin
  • Use the exact protective-device time/current basis and measured source impedance before treating the result as a design check.

Related calculators

Use the exact protective-device time/current basis and measured source impedance before treating the result as a design check.