Cable fault rating calculator
Cable fault rating calculator para sa New Zealand at Australia. Galing ang k factor sa AS/NZS 3008.1.2:2017, o sa AS/NZS 3008.1.1:2025 na puwedeng piliin ang 2017.
Reads AS/NZS 3008.1.2:2017 (NZ) and AS/NZS 3008.1.1:2017 and 2025 (AU). Tables checked 27 Sept 2026.
Subukan ang isang job 6
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Check a conductor against fault currentWhether a 35 mm² XLPE conductor withstands 10 kA for 0.2 s.
- Check consumer mains against 6 kAWhether 16 mm² mains withstand 6 kA for 0.1 s.
- Check a final circuit against 3 kAWhether 2.5 mm² withstands 3 kA for 0.1 s.
- Check an aluminium feederWhether 95 mm² aluminium withstands 20 kA for 0.3 s.
- Check a one-second withstandWhether 120 mm² withstands 25 kA for 1 s.
- Check a cable with a soldered jointThe lower limit a soldered joint sets on a 25 mm² cable.
Mga input
Worked example gamit ang mga default na input.
- Prospective fault current
- 6 kA
- Clearing time
- 0.1 s
- Standard
- NZ · AS/NZS 3008.1.2
- Laki ng conductor
- 25 mm²
- Material
- Tanso
- Insulation
- PVC 75 °C
- Insulation class
- Mula sa insulation ng cable
- Joint sa run
- Walang joint
Pinakamaliit na laki ng conductor
17.09mm²
- Napiling sukat
- 25mm²
- Kayang tiisin ang fault current
- 8.78kA
- k factor
- 111
- Limitasyon ng temperatura
- 160°C
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Starting temperature ng conductor75°C
AS/NZS 3008.1.2:2017 Table 53
- Limit ng temperatura sa short-circuit160°C
AS/NZS 3008.1.2:2017 Table 53
- k factor×111.00
AS/NZS 3008.1.2:2017 Table 52 p.121
- Pinakamaliit na laki ng conductorResulta17.09mm²
AS/NZS 3008.1.2:2017 Cl 5.3
- Withstand fault current8.78kA
AS/NZS 3008.1.2:2017 Cl 5.3
Tungkol sa calculator na ito
How this is calculated
The tool checks that a conductor survives a fault current for the time the protective device takes to clear it. It uses the adiabatic equation, S = √(I²t) / k. It assumes that no heat leaves the conductor during the fault.
- Temperatures. It reads the start temperature and the short-circuit temperature limit for the insulation. The insulation class select can name a 110 °C cross-linked type. A joint in the run can set a lower limit than the insulation.
- k factor. It reads k from Table 52 for the conductor material and the two temperatures. A larger temperature rise gives a larger k.
- Minimum size. S = √(I²t) / k gives the smallest conductor, in mm², that stays within the limit. I is the fault current in amperes and t is the clearing time in seconds.
- Withstand. It turns the equation round for the size you pick: I = k × S / √t. That is the largest fault current the conductor survives for that time.
- Result. The size you pick passes when it is at or above the minimum.
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. Take the clearing time from the device curve at the fault current. A longer time needs a larger conductor.
| Step | Table or clause | What it decides |
|---|---|---|
| Temperatures | Table 53 | The start temperature and the limit for the insulation |
| Joint | Table 55 | A lower limit where the joint sets it |
| k factor | Table 52 | The k for the material and the two temperatures |
| Minimum size and withstand | Cl 5.3 | The adiabatic check itself |
Tables without a standard named are in the part of AS/NZS 3008.1 you pick.
Common faults, worked with the tool
Each line states its conductor. Every line uses copper and the New Zealand tables, with no joint unless the line names one.
- Submain, 6 kA for 0.1 s on 25 mm² PVC. The minimum size is 17.09 mm² with a k of 111. The 25 mm² cable withstands 8.78 kA.
- The same fault on 25 mm² XLPE. The minimum size is 13.27 mm² with a k of 143. The cable withstands 11.31 kA.
- 25 mm² XLPE with a soldered joint. The joint sets the limit at 160 °C. The minimum size is 18.99 mm² with a k of 99.9. The cable withstands 7.9 kA.
- 10 kA for 0.2 s on 16 mm² PVC. The minimum size is 40.29 mm² with a k of 111, so it fails. The 16 mm² cable withstands 3.97 kA.
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.
See also: Prospective fault current at a main switchboard, Arc flash incident energy at a 400 V switchboard and Short-circuit withstand and the k factor.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Ano ang ginagawa ng fault rating calculator?
Ina-apply ng tool ang adiabatic check sa conductor. Mula sa prospective fault current at sa clearing time, kinakalkula nito ang minimum size. Iniuulat din nito ang fault current na kayang tiisin ng inilagay na laki sa oras na iyon. Pumapasa ang check kapag hindi mas mababa sa minimum ang naka-install na laki.
Saan galing ang k factor?
Galing ang k factor sa AS/NZS 3008.1.2:2017 Table 52. Nakadepende ito sa conductor material at sa uri ng insulation. Ang bumagsak na check ay tumutukoy sa AS/NZS 3008.1.2:2017 Clause 5.3, na nagbibigay ng adiabatic equation na I²t = K²S². Kapag binago ang material o insulation, nagbabago rin ang k factor.
Ano ang nagtatakda ng minimum cable size para sa fault?
Itinutulak ng prospective fault current at ng clearing time ang minimum size. Dapat tumugma ang clearing time sa device na nag-aalis ng fault, hindi sa downstream device. Itinatakda ng material at insulation ang k factor. Ang mga cable na parallel ay itinuturing na isang conductor na may pinagsamang cross section.
Ano ang hindi sakop ng check na ito?
Hindi nito tinitingnan ang current rating, voltage drop o loop impedance. Gamitin ang cable size tool para sa mga check na iyon. Ipinapalagay din ng adiabatic method na walang init na lumalabas sa conductor habang may fault. Nasa page address ang mga input, kaya inuulit ng link ang parehong check.
Binabago ba ng laki ng conductor o ng joint ang k factor?
Oo. Ibinababa ng AS/NZS 3008.1.2:2017 Table 53 ang thermoplastic limit mula 160 patungong 140 degrees kapag higit sa 300 square millimetres. Nililimitahan ng Table 55 ang soldered joint sa 160 degrees. Binabasa ng tool ang dalawa, pagkatapos ay kinukuha ang k factor para sa start at limit pair na iyon mula sa Table 52.
Mga worked example
- Switchboard fault rating at 25 kA for 1 sA 1 second withstand check at 25 kA on 185 mm² copper XLPE, returning a 174.83 mm² minimum size and a 26.46 kA withstand, with a thin margin explained.
- Consumer mains fault withstand for 16 mm² copperA domestic 6 kA fault cleared in 10 milliseconds against 16 mm² copper PVC mains, giving a 5.41 mm² minimum size and a 17.76 kA adiabatic withstand.
- 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.
- AS/NZS 3008.1.2 Table 52: the k factorWhat Table 52 governs, how the adiabatic check uses k, and a 10 kA fault cleared in 0.1 s that needs 22.11 mm² against an installed 25 mm² conductor.
- AS/NZS 3008 vs BS 7671: cable sizing comparedHow BS 7671 and AS/NZS 3000 with AS/NZS 3008.1 size a cable, where they differ, and why a BS current rating never converts into an AS/NZS one.
- Prospective fault current at a main switchboardA 16 kA fault cleared in 0.1 s on 70 mm² copper XLPE, with the minimum conductor size, the withstand current and the k factor the adiabatic check returns.
Background
- MEN system: multiple earthed neutral explainedMEN means multiple earthed neutral. In NZ, earth and neutral join at the main switchboard. A fault on a 32 A C curve circuit then draws 343.8 A and clears.
- Earthing conductor size: table or calculationHow the protective earthing conductor, the main earthing conductor and the bonding conductor are sized, worked on a 25 mm² active with a 3 kA fault.
- IB ≤ IN ≤ IZ: the overload rule on a 32 A circuitThe overload rule is IB ≤ IN ≤ IZ. A grouped 32 A circuit fails on 6 mm² and passes on 10 mm², with an IZ of 37.6 A. Why the order matters.
- Short-circuit withstand and the k factorThe adiabatic check in plain terms: prospective fault current, clearing time and k, worked on 25 mm² copper XLPE at 10 kA for 0.1 s.
- Arc flash basicsArcing current, incident energy, boundary and working distance explained, with three engine runs that show clearing time beating fault current every time.
- Industrial switchboards: fault rating, form, IPWhat the three ratings on an industrial switchboard or motor control centre mean, how each one is chosen, and which AmpSize tools feed the numbers behind them.
Mga clause at table na binabasa ng tool na ito
- AS/NZS 3008.1.2:2017 Cl 5.3Short-circuit performance
- AS/NZS 3008.1.2:2017 Cl 5.5.1Short-circuit duration
- AS/NZS 3008.1.2:2017 Table 52Values of constant K for determination of permissible short-circuit currents
- AS/NZS 3008.1.2:2017 Table 52, 53, 54, 55Short-circuit K values and temperature limits
- AS/NZS 3008.1.1:2017 Table 52Values of constant K for determination of permissible short-circuit currents
- AS/NZS 3008.1.1:2017 Table 52, 53, 54, 55Short-circuit K values and temperature limits
- AS/NZS 3008.1.1:2025 Table 5.1Values of constant K for determination of permissible short-circuit currents
- AS/NZS 3008.1.1:2025 Table 5.1, 5.2, 5.3, 5.4Short-circuit K values and temperature limits
Bawat clause at table, kasama kung paano ito na-verify
Huling na-check ang mga table noong 27 Sept 2026.
Mga kaugnay na tool
- Fault level calculatorProspective fault current at a board from its source.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
- Earth fault loop impedance calculatorCheck earth fault loop impedance against the maximum Zs.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
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