Maximum circuit length calculator
Pinakamahabang run na pinapayagan ng voltage drop at ng fault loop.
Reads AS/NZS 3008.1.2:2017 (NZ) and AS/NZS 3000:2018. Tables checked 26 Sept 2026.
Subukan ang isang job 6
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Find the longest run for a lighting circuitThe longest route a 1.5 mm² lighting circuit on a 10 A breaker can take.
- Find the longest socket circuitThe longest run for a 20 A circuit on 2.5 mm².
- Find the longest oven circuitThe longest run for a 32 A circuit on 6 mm², by voltage drop.
- Find the longest motor circuitThe longest three‑phase run on a 16 A D‑curve breaker.
- Find the longest run at 3 %The longest run when the drop limit is 3 %.
- Find the longest heat pump runThe longest run for a 16 A C‑curve circuit on 2.5 mm².
Mga input
Worked example gamit ang mga default na input.
- Active conductor
- 2.5 mm²
- Earth conductor
- 2.5 mm²
- Insulation
- PVC
- Protective device
- Type B circuit-breaker
- Device rating
- 20 A
- Mga phase
- Single phase
- Nominal phase voltage
- 230 V
- Design current
- 20 A
- Power factor
- 0.9
- Limit ng voltage drop
- 5 %
Pinakamahabang haba ng ruta
35.26m
- Haba ng ruta ng fault loop
- 128m
- Haba ng ruta ng voltage drop
- 35.26m
- Governing check
- Voltage drop
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Haba ng ruta ng fault loop128m
AS/NZS 3000:2018 Table B1
- Resistance ng copper conductor sa operating temperature9.01Ω/km
AS/NZS 3008.1.2:2017 Table 30, Tables 34 to 35
- Reactance0.1Ω/km
AS/NZS 3008.1.2:2017 Table 30, Tables 34 to 35
- Voltage drop kada amp metre16.31mV/A·m
AS/NZS 3008.1.2:2017 Table 30, Tables 34 to 35
- Ang voltage kung saan kinukuha ang limitasyon ng drop230V
AS/NZS 3000:2018 Cl 3.6.2
- Limitasyon ng voltage drop11.5V
AS/NZS 3000:2018 Cl 3.6.2
- Haba ng ruta ng voltage drop35.26m
AS/NZS 3000:2018 Cl 3.6.2
- Governing lengthResulta35.26m
AS/NZS 3000:2018 Cl 3.6.2
Tungkol sa calculator na ito
How this is calculated
The tool finds the longest final subcircuit route that two limits each allow. It reports which limit governs. It reads AS/NZS 3000:2018 and AS/NZS 3008.1.2:2017.
- Fault loop length. The tool reads the route length for your breaker, size and earth size from Table B1.
- Resistance and reactance. It reads these for the active conductor. The tables are Table 30 and Tables 34 and 35, for copper at operating temperature.
- Millivolts per ampere metre. It combines both values with your power factor.
- Voltage drop limit. Cl 3.6.2 sets the limit. You enter it as a percentage of the supply voltage.
- Voltage drop length. It finds the route length at which the drop equals the limit for your design current.
- Governing length. The shorter of the two lengths is the maximum route length.
| Step | Table or clause | What it decides |
|---|---|---|
| Fault loop length | AS/NZS 3000:2018 Table B1 | The longest route for the breaker to trip |
| Cable data | AS/NZS 3008.1.2:2017 Tables 30, 34 and 35 | Resistance and reactance |
| Voltage drop length | AS/NZS 3000:2018 Cl 3.6.2 | The longest route within the drop limit |
Worked example
- 2.5 mm² on a 20 A type B breaker. The earth is 2.5 mm², with PVC insulation, on a single‑phase 230 V supply. The design current is 20 A at a power factor of 0.9. The fault loop route length is 128 m. The voltage drop route length is 35.26 m. The voltage drop governs, so the maximum route length is 35.26 m.
Limits
The tool assumes copper conductors. The reactance is the Table 30 value for a multicore cable. A single‑core run reads a higher reactance for its formation.
The tool does not check the current rating of the cable. It does not add correction factors. Use the cable size calculator for the full check.
See also: Maximum length of a 20 A final subcircuit, The voltage drop limit in Cl 3.6.2 and the voltage drop calculator.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Ano ang ginagawa ng Maximum Circuit Length tool?
Iniuulat ng tool ang dalawang haba. Ang una ay ang haba ng ruta na nagpapahintulot pa rin sa protective device na mag-disconnect sa tamang oras. Ang ikalawa ay ang haba kung saan umaabot ang voltage drop sa limit mo. Ang mas maikli sa dalawa ang nagdidikta sa run.
Saan galing ang dalawang haba?
Galing ang fault loop length sa AS/NZS 3000:2018 Table B1 para sa 0.4 s disconnection time sa 230 V, na in-scale ayon sa nominal voltage mo. Ginagamit ng voltage drop length ang resistance at reactance mula sa AS/NZS 3008.1.2:2017 Tables 30, 34 at 35, laban sa Clause 3.6.2.
Bakit walang fault loop length na lumalabas para sa kombinasyon?
Nakalista sa Table B1 ang nakapirming listahan ng conductor pair at device rating. Ang pair na hindi nakalimbag ay walang nakalistang haba, kaya voltage drop length lang ang iniuulat ng tool. Gamitin na lang ang loop impedance tool para suriin ang kombinasyong iyon.
Mga clause at table na binabasa ng tool na ito
- B1Maximum route lengths for conductor sizes and protective devices
- AS/NZS 3008.1.2:2017 Table 30, 34, 35Reactance 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 26 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
- Voltage drop calculatorCalculate voltage drop on a cable run and check the limit.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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