अर्थ फ़ॉल्ट लूप इम्पीडेंस कैलकुलेटर

How this is calculated#

The tool works out the earth fault loop impedance of one circuit. It compares that impedance with the maximum for the protective device.

1. Earth conductor. If you leave the earth size on From Table 5.1, the tool picks it from the active conductor size.
2. R1 + R2. It reads the resistance of the active and the earth conductors at their operating temperature. The Standard select decides which part it reads. It reads AS/NZS 3008.1.2 for New Zealand or AS/NZS 3008.1.1 for Australia. It adds the two and multiplies by the run length.
3. Zs. It adds the external impedance: Zs = Ze + (R1 + R2).
4. Maximum Zs. It reads the maximum for the device curve and rating from AS/NZS 3000 Table 8.1. The circuit passes when Zs is at or below that maximum.
5. Fault current. It divides the voltage by Zs to get the prospective fault current.
6. Maximum length. It works out the run length at which Zs reaches the maximum.

Ze is a site value. Measure it, or ask the network operator for it. The tool warns when Ze alone takes 90 % or more of the limit. After you install the circuit, test it and compare the measured Zs with the calculated one.

Tables without a standard named are in the part of AS/NZS 3008.1 you pick. The Table 8.1 guide explains why the B, C and D curve limits differ.

Common circuits, worked with the tool#

Each line states its route. Every line uses copper cable with PVC insulation, a Ze of 0.35 Ω at 230 V and the New Zealand tables. The earth size comes from Table 5.1.

• Socket‑outlets, 16 A B curve over 30 m of 2.5 mm². Zs is 0.89 Ω against a maximum of 3.59 Ω. The prospective fault current is 258.25 A.
• Cooker, 32 A C curve over 25 m of 6 mm². Zs is 0.67 Ω against a maximum of 0.96 Ω. The earth conductor is 2.5 mm².
• The same cooker circuit over 40 m. Zs is 0.86 Ω against a maximum of 0.96 Ω. The run can reach 47.68 m.
• Motor, 20 A D curve over 50 m of 2.5 mm². Zs is 1.25 Ω against a maximum of 0.92 Ω, so it fails. The run can reach 31.63 m.

New Zealand and Australia#

The Standard select picks the part of AS/NZS 3008.1 for the conductor resistance. Table 8.1 and Table 5.1 are in AS/NZS 3000, which is the same in both countries.

Keep the result#

Every input sits in the page address, so the link in your browser reproduces the calculation. The PDF button prints the result with its steps and table references. Saving a calculation to a project needs a free account.