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

Earthing Conductor Sizing

Earthing conductor sizing per AS/NZS 3000 Clause 5.4.

1. Input Parameters

Fault and conductor parameters for earthing conductor sizing:
Parameter Symbol Value Notes
Fault Current I_f 10 kA Prospective earth fault current
Clearing Time t 400 ms Protective device clearing time
Conductor Material Cu
Insulation Type PVC
Active Conductor Size A_{active} 50 mm² For Table 5.1 lookup

2. k-Factor Selection

Material: Cu, Insulation: PVC k-factor = 115 (AS/NZS 3008.1 Table 52)

3. Adiabatic Equation

Minimum conductor area from adiabatic equation (A = I√t/k):

Formula: $$ \begin{aligned} A &= \frac{I \sqrt{t}}{k} \\ &= \frac{10000 \times \sqrt{0.4}}{115} \\ &= 55 \; \text{mm}^2 \end{aligned} $$

4. Table 5.1 Lookup

Active conductor size: 50.0 mm² Minimum earth conductor per Table 5.1: 16 mm²

5. Governing Minimum

Adiabatic minimum: 55.0 mm² Table 5.1 minimum: 16 mm² Governing minimum: 55.0 mm² (larger of the two)

6. Standard Size Selection

Governing minimum: 55.0 mm² Selected standard size: 70 mm²

7. Thermal Withstand Verification

Maximum withstand time for selected conductor:

Formula: $$ \begin{aligned} t_{max} &= \left( \frac{A \times k}{I} \right)^2 \\ &= \left( \frac{70 \times 115}{10000} \right)^2 \\ &= 0.648 \; \text{s} \end{aligned} $$

8. Summary

Selected earthing conductor: 70 mm² Cu (PVC) OVERALL: PASS - Withstand time (0.65 s) >= Clearing time (0.4 s)

Approval:

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Created By
Engineer Name
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Checked
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Approved
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