Pagsusuri ng umiiral na circuit
Tingnan ang naka-install na circuit: cable, device, drop at Zs.
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 7
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Check the breaker on a 4 mm² circuitWhether a 32 A breaker suits 4 mm² cable, and the largest breaker the cable allows.
- Check an existing three‑phase submainWhether 16 mm² on a 63 A breaker over 80 m passes the cable, drop and Zs checks.
- Check a 20 A breaker on 2.5 mm²Whether a 20 A breaker suits a 2.5 mm² circuit.
- Check a 32 A breaker on 6 mm²Whether a 32 A breaker suits a 6 mm² circuit.
- Check a 16 A breaker on 1.5 mm²Whether a 16 A breaker suits a 1.5 mm² circuit.
- Check a 63 A breaker on 16 mm²Whether a 63 A breaker suits 16 mm² mains.
- Check a 10 A breaker on 1 mm²Whether a 10 A breaker suits a 1 mm² lighting circuit.
Mga input
Worked example gamit ang mga default na input.
- Mga phase
- Single phase
- Voltage
- 230 V
- Design current
- 20 A
- Power factor
- 0.9
- Standard
- NZ · AS/NZS 3008.1.2
- Haba ng run
- 30 m
- Installation method
- Enclosed sa hangin
- Ambient na temperatura
- 30 °C
- Naka-group na circuit
- 1
- Laki ng naka-install na cable
- 2.5 mm²
- Material
- Tanso
- Insulation
- PVC 75 °C
- Mga core
- Multicore
- Mga cable na parallel
- 1
- Limit ng voltage drop
- 5 %
- External impedance Ze
- 0.35 Ω
- Prospective fault current
- 0 kA
- Curve ng device
- Curve C
- Device rating
- 20 A
Circuit na 2.5 mm²
Pumapasa
- Itinamang rating Iz
- 23A
- Voltage drop
- 4.25%
- Earth fault loop impedance
- 0.89Ω
- Pinakamataas na Zs para sa device
- 1.53Ω
- Pinakamaliit na laki na pumapasa
- 2.5mm²
- Pinakamalaking device na C curve na pinapayagan ng cable
- 20A
- Pinagsamang correction factor
- ×1.00
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Laki ng naka-install na conductor2.5mm²
AS/NZS 3008.1.2:2017 Table 13 p.62–64
- Tabulated rating ng 2.5 mm²23A
AS/NZS 3008.1.2:2017 Table 13 p.62–64
- Ambient correction factor×1.00
AS/NZS 3008.1.2:2017 Tables 27(1), 27(2) p.88
- Correction factor ng grouping×1.00
One circuit, no grouping factor
- Pinagsamang correction factor×1.00
- Naitamang rating Iz23A
AS/NZS 3000:2018 Cl 3.4
- Voltage drop9.78V
- Voltage drop percent4.25%
AS/NZS 3000:2018 Cl 3.6.2
- Device rating In20A
AS/NZS 3000:2018 Cl 2.5.3.1
- Laki ng earth conductor2.5mm²
AS/NZS 3000:2018 Table 5.1
- Earth fault loop impedance sa 230 V phase sa earth0.89Ω
AS/NZS 3000:2018 Table 8.1
- Pinakamataas na Zs para sa device1.53Ω
AS/NZS 3000:2018 Table 8.1
- Pinakamaliit na sukat na pumapasa2.5mm²
AS/NZS 3000:2018 Cl 3.4
Tungkol sa calculator na ito
How this is calculated
The tool takes a circuit that is already installed and runs the five checks of the cable size calculator at its size. It uses the same code, so the two tools agree on every size.
- Current capacity. It reads the tabulated rating of the installed size for your material, insulation, core count and installation method. It multiplies the rating by the correction factors for the route to get Iz. Iz must be at or above the design current Ib.
- Voltage drop. It works out the drop for the run length, the power factor and the conductor. It compares the drop with the limit you set.
- Breaker rating. The breaker rating In must sit between the two: Ib at or below In, and In at or below Iz. The tool gives both margins.
- Loop impedance. It adds the active and earth conductor resistance to the external impedance Ze. The total Zs must stay under the maximum for the breaker curve and rating.
- Fault withstand. If you enter a prospective fault current, the conductor must withstand it for the clearing time.
- Result. The circuit passes when every check it runs passes. The tool gives the smallest standard size that passes with the same breaker, and the largest breaker of the same curve that the cable allows.
| Step | Table or clause | What it decides |
|---|---|---|
| Current rating | Table 13 or 14 for multicore, Tables 4, 5, 7 and 8 for single core | The tabulated rating of the installed size |
| Correction factors | Tables 22 to 29 and Table 2 | The factors for the route |
| Voltage drop | Tables 30, 34 and 35, AS/NZS 3000 Cl 3.6.2 | The drop over the run and its limit |
| Breaker rating | AS/NZS 3000 Cl 2.5.3.1 | That In sits between Ib and Iz |
| Earth and Zs | AS/NZS 3000 Table 5.1 and Table 8.1 | The earth conductor size and the maximum loop impedance |
| Fault withstand | Table 52 and Cl 5.3 | The fault current the conductor survives |
Tables without a standard named are in the part of AS/NZS 3008.1 you pick. AS/NZS 3008.1.1:2025 numbers them by section.
Common circuits, worked with the tool
Each line states its circuit. Every line uses multicore copper cable with PVC insulation and one circuit on the route, enclosed in air at 30 °C. Every breaker is a C curve and Ze is 0.35 Ω, on the New Zealand tables.
- Socket‑outlets, 2.5 mm² on a 20 A breaker over 30 m. It passes every check. The drop is 4.25 %, close to the 5 % limit.
- The same cable on a 32 A breaker with a 25 A load. It fails the current, drop and breaker checks. 6 mm² is the smallest size that passes.
- 4 mm² on a 32 A breaker over 20 m. It fails the breaker check, because Iz is 29 A. The largest breaker the cable allows is 25 A, and 6 mm² is the smallest size that passes on 32 A.
- Three‑phase submain, 16 mm² on a 63 A breaker over 80 m. It fails on loop impedance: Zs is 0.76 Ω against a maximum of 0.49 Ω. With this breaker, 70 mm² is the smallest size that passes.
New Zealand and Australia
The Standard select picks the part of AS/NZS 3008.1 the tool reads. For Australia, the Edition select picks 2025 or the superseded 2017 edition. The breaker and Zs rules come from AS/NZS 3000, which is the same in both countries.
What the tool does not check
The tool works from the inputs, not from a test. Measure Ze and Zs on site and compare the reading with the maximum it gives. It does not check RCD rules or discrimination between breakers.
To size a new circuit, use the cable size calculator. To read the factors for a route on their own, use the correction factors calculator.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Anong laki ng breaker ang puwede sa 4 mm² cable?
Depende ito sa route. Kapag nakabalot sa 30 °C na hangin nang mag-isa, ang 4 mm² copper ay rated 29 A sa New Zealand, kaya ang 25 A breaker ang pinakamalaking standard size. Ibinababa ito ng grouping, init o insulation. I-enter ang route mo para mabasa ang pinakamalaking breaker na pinapayagan ng cable.
Ano ang ibig sabihin ng Ib ≤ In ≤ Iz?
Ang Ib ay ang design current ng load, ang In ay ang rating ng breaker, at ang Iz ay ang cable rating pagkatapos ng correction. Dapat kayanin ng breaker ang load, at dapat kayanin ng cable ang rating ng breaker. Itinatakda ng AS/NZS 3000 Clause 2.5.3.1 ang rule.
Bakit bumabagsak ang mahabang circuit sa loop impedance?
Mataas ang earth fault loop impedance ng mahaba o maliit na cable. Dahil dito, masyadong mababa ang fault current para mag-trip agad ang breaker sa magnetic setting nito. Gumamit ng mas malaking cable, mas mababang breaker rating, B curve, o tingnan ang RCD rules para sa circuit.
Sinusukat ba ng tool ang circuit ko?
Hindi. Gumagana ito batay sa cable size, sa ruta, at sa external impedance na Ze na ilalagay mo. Sukatin ang Ze at Zs sa site at ikumpara ang reading sa maximum Zs na ibinibigay ng tool.
Anong laki ang iminumungkahi ng tool kapag bumagsak ang circuit?
Ang pinakamaliit na standard size na pumapasa sa bawat check gamit ang parehong breaker, ruta at load. Ito ang sagot na ibinibigay ng cable size calculator para sa parehong circuit.
Mga worked example
- A circuit chart for a house board with solarThe circuit chart and labels for a six-circuit house board with a solar inverter: ways, devices, RCDs, MAIN SWITCH, MAIN SWITCH SOLAR and a shared neutral.
- What size breaker for 4 mm² cable4 mm² copper enclosed in air takes a 25 A breaker, and 32 A fails at an Iz of 29 A. Grouping, a hot ceiling, insulation and a long run lower it.
Background
Mga clause at table na binabasa ng tool na ito
- AS/NZS 3000:2018 Cl 2.5.3.1Protective device coordination
- AS/NZS 3000:2018 Cl 3.4Current-carrying capacity
- AS/NZS 3000:2018 Cl 3.6.2Voltage drop limit
- AS/NZS 3000:2018 Table 5.1Minimum earthing conductor size by active conductor size
- AS/NZS 3000:2018 Table 8.1Maximum earth fault loop impedance multipliers by MCB curve
- AS/NZS 3008.1.2:2017 Table 4Current ratings, single‑core cable, two cables per circuit, thermoplastic 75 °C
- AS/NZS 3008.1.2:2017 Table 5Current ratings, single‑core cable, two cables per circuit, cross-linked 90 °C
- AS/NZS 3008.1.2:2017 Table 7Current ratings, single‑core cable, three cables per circuit, thermoplastic 75 °C
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 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
- Simplified cable selectorRead the Appendix C device rating and voltage drop tables.AS/NZS 3000
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