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Calculation No.: Calc-001
Revision: A
Description:
Created By: Engineer Name
Project: Project Name
Project No.: P001
Client: Client Name

Earth Fault Loop Impedance Calculation

Earth fault loop impedance (Zs) calculation per IEC 60364 / AS/NZS 3000.

1. Input Parameters

Circuit parameters for earth fault loop impedance calculation:
Parameter Symbol Value Notes
Nominal Voltage U_o 230 V Phase-to-neutral
Breaker Rating I_n 20 A Nominal current
Trip Curve k C (x7.5) Multiplier: 7.5
Insulation Type PVC (75°C)
Active CSA A_1 4 mm² Active conductor
Earth CSA A_2 4 mm² Main earth conductor
Cable Length L 50 m

3. Individual Conductor Impedances

Impedance = (per-km value) × (length / 1000). Insulation: PVC (75°C).

Formula: $$ Z = R + jX = (r \times \frac{L}{1000}) + j(x \times \frac{L}{1000}) $$
Parameter Symbol Value Notes
Active (Z₁) 4mm² @ 50.0m R=0.2805, X=0.0051 |Z|=0.2805
Main Earth (Z₂) 4mm² @ 50.0m R=0.2805, X=0.0051 |Z|=0.2805

4. Equivalent Earth Path Impedance (Ze)

No supplementary earthing — Ze = Z₂ = 0.2805 + j0.0051 Ω (|Ze| = 0.2805 Ω)

5. Cable Loop Impedance (Z_cable)

Sum of active and equivalent earth path impedances: |Z_cable| = 0.5611 Ω

Formula: $$ \begin{aligned} Z_{cable} &= Z_1 + Z_e \\ &= (0.281 + 0.281) + j(0.0051 + 0.0051) \\ &= 0.561 + j0.0102 \; \Omega \end{aligned} $$

6. Trip Current (Ia)

Minimum fault current required for instantaneous trip:

Formula: $$ \begin{aligned} I_a &= I_n \times k_{trip} \\ &= 20 \times 7.5 \\ &= 150 \; \text{A} \end{aligned} $$

7. Maximum Allowed Impedance (Zmax)

Maximum earth fault loop impedance for disconnection within required time:

Formula: $$ \begin{aligned} Z_{max} &= \frac{U_o}{I_a} \\ &= \frac{230}{150} \\ &= 1.53 \; \Omega \end{aligned} $$

8. Total Earth Fault Loop Impedance (Zs)

Zs = transformer impedance + cable loop impedance:

Formula: $$ \begin{aligned} Z_s &= Z_t + Z_{cable} \\ &= (0 + 0.561) + j(0 + 0.0102) \\ &= 0.561 + j0.0102 \; \Omega \end{aligned} $$

8.1 Zs Magnitude

Formula: $$ \begin{aligned} |Z_s| &= \sqrt{R_{total}^2 + X_{total}^2} \\ &= \sqrt{0.561^2 + 0.0102^2} \\ &= 0.561 \; \Omega \end{aligned} $$

9. Compliance Check

|Zs| = 0.5611 Ω vs Zmax = 1.5333 Ω → PASS Table 8.2: Not applicable for this CSA/CB combination. Table B1: Length = 50.0 m vs limit = 67.0 m → PASS OVERALL: PASS - Circuit Compliant
Parameter Symbol Value Notes
Earth Fault Loop Impedance Zs 0.5611
Maximum Allowed Impedance Zmax 1.5333
Prospective Fault Current If 409.9 Uo / Zs
Trip Current Ia 150.0 In × multiplier
Result PASS

Approval:

This calculation has been reviewed and approved by:
Created By
Engineer Name
Date: ..........................
Checked
By: .............................
Date: ..........................
Approved
By: .............................
Date: ..........................
Client Approved
By: .............................
Date: ..........................

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