Fault level calculator
Prospective fault current sa board mula sa source nito.
Reads AS/NZS 3008.1.2:2017 (NZ), AS/NZS 3008.1.1:2017 and 2025 (AU) and AS/NZS 3000:2018. Tables checked 27 Sept 2026.
Subukan ang isang job 8
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Find the fault level at a sub‑boardThe fault current at a board 45 m from a 300 kVA transformer, against 6 kA breakers.
- Check breakers beside a 1000 kVA transformerWhether 25 kA breakers suit a main board 20 m from a 1000 kVA transformer.
- Find the fault level at a house boardThe fault current at the end of 20 m of 16 mm² mains.
- Find the fault level at a shedThe fault current 60 m down a 16 mm² submain.
- Find the fault level at an MCCThe fault current 30 m from a 500 kVA transformer.
- Check 6 kA breakers at a tenancy boardWhether 6 kA devices suit the fault level at the board.
- Find the fault level on parallel feedersThe fault current with two cables per phase.
- Find fault level from a 10 kA serviceThe fault current at a board in Australia.
Mga input
Worked example gamit ang mga default na input.
- Pinagmulan
- Transformer
- Rating ng transformer
- 500 kVA
- Transformer impedance
- 4.5 %
- Line voltage
- 400 V
- Standard
- NZ · AS/NZS 3008.1.2
- Haba ng submain
- 30 m
- Laki ng conductor
- 35 mm²
- Material
- Tanso
- Insulation
- PVC 75 °C
- Mga core
- Multicore
- Mga cable na parallel
- 1
- Breaking capacity ng circuit-breaker
- 15 kA
Three-phase fault current sa board
10.01kA
- Phase-earth fault current, maximum
- 3.18kA
- Phase-earth fault current, cable hot
- 2.63kA
- Source impedance kada phase
- 14.4mΩ
- Breaking capacity
- 15kA
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Impedance ng transformer kada phase, U² ÷ S × Z%0.01Ω
- Fault current sa source16.04kA
- Submain phase resistance sa operating temperature0.02Ω
AS/NZS 3008.1.2:2017 Table 30 (Xc), Tables 34–35 (Rc) p.98, p.102–103
- Submain phase resistance sa 20 °C0.02Ω
AS/NZS 3008.1.2:2017 Table 30 (Xc), Tables 34–35 (Rc) p.98, p.102–103
- Submain phase reactance0Ω
AS/NZS 3008.1.2:2017 Table 30 (Xc), Tables 34–35 (Rc) p.98, p.102–103
- Laki ng protective conductor10mm²
AS/NZS 3000:2018 Table 5.1
- Protective conductor resistance sa 20 °C0.06Ω
AS/NZS 3008.1.2:2017 Table 30 (Xc), Tables 34–35 (Rc) p.98, p.102–103
- Three‑phase fault current sa board, U0 ÷ |Z|Resulta10.01kA
- Phase-earth fault current sa board, pinakamataas3.18kA
- Phase-earth fault current, cable sa operating temperature2.63kA
- Breaking capacity ng circuit-breaker15kA
Tungkol sa calculator na ito
How this is calculated
The tool finds the fault current at a board. The source is a transformer or a stated supply fault level. A submain then adds impedance. The tool compares the result with the breaking capacity of your device.
- Source impedance. For a transformer, the tool works Z = U² ÷ S × Z% per phase. It takes the source as all reactance. That gives the highest current for the size.
- Source current. It gives the fault current at the transformer terminals.
- Submain impedance. It reads the resistance and reactance of the submain for your size, length and material. The tables are Table 30 for reactance and Tables 34 and 35 for resistance. It scales the resistance to 20 °C for the maximum figure.
- Protective conductor. It reads the earth conductor size from Table 5.1 of AS/NZS 3000:2018. It adds that resistance to the earth loop.
- Fault currents. It gives the three‑phase current as U0 ÷ |Z|. It also gives the phase-earth current, maximum and with the cable hot.
- Breaking capacity. It compares the three‑phase current with the rating you enter.
| Step | Table or clause | What it decides |
|---|---|---|
| Submain reactance | AS/NZS 3008.1.2 Table 30 | The reactance of the submain |
| Submain resistance | AS/NZS 3008.1.2 Tables 34 and 35 | The resistance of the submain |
| Earth conductor | AS/NZS 3000 Table 5.1 | The size of the protective conductor |
Worked example
- 500 kVA transformer with a 30 m 35 mm² submain. The transformer has 4.5 % impedance. The three‑phase fault current at the board is 10.01 kA. The maximum phase-earth current is 3.18 kA. A 15 kA device passes.
Limits
- The tool works at nominal voltage. It does not apply the IEC 60909 voltage factors.
- It takes the network above the transformer as infinite. A real network lowers the current a little.
- It takes the phase-earth loop at the transformer as its phase impedance, as for a Dyn transformer.
- It does not add motor contribution. It does not grade devices. Use the IDMT tool for grading.
- The result is an estimate for sizing. Ask the network company for the supply fault level at the point of supply.
See also: Prospective fault current at a board, Fault level at a sub‑board on a 300 kVA transformer and Fault rating.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Paano kinakalkula ng fault level tool ang current?
Idinadagdag nito ang impedance kada phase. Ang transformer ay nagbibigay ng U² ÷ S × Z%, at ang supply ay nagbibigay ng phase voltage na hinati sa fault level nito. Idinadagdag ng submain ang resistance at reactance nito mula sa AS/NZS 3008.1 impedance tables. Ang phase voltage na hinati sa kabuuan ang three‑phase fault current sa board.
Bakit may dalawang phase-earth figure?
Nakalista sa table ang resistance sa operating temperature ng conductor. Ang malamig na cable ang nagbibigay ng pinakamataas na current, kaya ang maximum ay ini-scale ang resistance sa 20 °C. Ang hot figure ang mas mababa, para sa disconnection time check sa loop impedance tool.
Ano ang ipinapalagay ng tool tungkol sa source?
Itinuturing nito ang source bilang puro reactance, at ang network sa itaas ng transformer bilang walang hanggan. Parehong nagbibigay ng pinakamataas na current para sa mga figure na iniinput mo. Gumagamit ito ng nominal voltage nang walang IEC 60909 voltage factor. Kailangan ng supply source ng Ze sa origin para sa phase-earth figures.
Ano ang gagawin ko sa resulta?
Ikumpara ito sa breaking capacity ng circuit-breaker sa board. Pagkatapos, dalhin ito sa fault rating tool, na tumitingin kung kayang tiisin ng mga cable ang fault sa clearing time.
Mga worked example
- Starting a loaded conveyorA 22 kW conveyor that needs 120 % torque to break away. Why star-delta and a soft starter will not start it, and what a drive or autotransformer does.
- Fault level at a sub‑board, 300 kVA transformerWork the prospective fault current at a sub‑board 45 m from a 300 kVA transformer, three‑phase and phase-earth, and check 6 kA and 10 kA breakers against it.
Background
Mga clause at table na binabasa ng tool na ito
- AS/NZS 3000:2018 Table 5.1Minimum earthing conductor size by active conductor size
- AS/NZS 3008.1.2:2017 Table 30, 34, 35Reactance at 50 Hz and a.c. resistance at 50 Hz
- AS/NZS 3008.1.1:2017 Table 30, 34, 35Reactance at 50 Hz and a.c. resistance at 50 Hz
- AS/NZS 3008.1.1:2025 Table 4.1(A), 4.1(B), 4.5(A), 4.5(B)Reactance at 50 Hz and a.c. resistance at 50 Hz
Bawat clause at table, kasama kung paano ito na-verify
Huling na-check ang mga table noong 27 Sept 2026.
Mga kaugnay na tool
- Cable fault rating calculatorCheck that a conductor can withstand the fault current.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- Cable size calculatorFind the smallest cable size that passes each check.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- Transformer calculatorCalculate transformer full load current and impedance.Walang standard
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