Iahiko neutral o tētahi uta kore taurite
Te Iahiko Neutral o tētahi uta wāhanga toru kāore i taurite.
Reads AS/NZS 3000:2018. Tables checked 2 Oct 2026.
Whakamātau mahi 4
Ka whakakī ia mahi i ngā uara tauira. Whakakapia ērā ki ō uara.
- Find the neutral current of a shop boardThe neutral current of a board with 45, 30 and 25 A on its phases.
- Neutral current with heaters and a motorHeaters on one phase and a motor on another: the neutral with two power factors.
- Neutral current of a farm on one phaseMost of the load on one phase: how close the neutral comes to that phase.
- Check the neutral of a mostly three‑phase loadThe out-of-balance current a reduced neutral must still carry.
Ngā whakauru
He tauira mahi me ngā whakauru taunoa.
- Voltage raina
- 400 V
- Au wāhanga A
- 32 A
- Au wāhanga B
- 20 A
- Au wāhanga C
- 10 A
- Tauwhāinga hiko, wāhanga A
- 1
- Tauwhāinga hiko, wāhanga B
- 1
- Tauwhāinga hiko, wāhanga C
- 1
Te au neutral
19.08A
- Te neutral hei wāhi o te wāhanga teitei rawa
- 59.6%
- Te au wāhanga teitei rawa
- 32A
- Te kaha pono, e toru ngā wāhanga
- 14.32kW
He āwhina hoahoa tēnei hua. Manatokohia ki te paerewa o nāianei.
Ngā hīkoi tātaitanga
- Au wae A, i 0° mai i te voltage wae A32A
- Au wae B, i −120° mai i te voltage wae A20A
- Au wae C, i 120° mai i te voltage wae A10A
- Tātai: kotahi te tauwehe pūngao, nō reira
I_N = √(Ia² + Ib² + Ic² − Ia·Ib − Ib·Ic − Ic·Ia)
19.08 A - Au koreHua19.08A
AS/NZS 3000:2018 Cl 3.5.2(b)(ii)
- Te koki o te au neutral mai i te wāhanga A−27
- Te neutral hei wāhi o te wāhanga teitei rawa59.6%
- Te kaha pono, e toru ngā wāhanga14.32kW
Mō tēnei tātaitai
How this is calculated
In a star load each phase current returns through the neutral. The three phase voltages are 120° apart, so the three currents are too. When the currents are equal and at one power factor, they cancel and the neutral carries nothing. When they are not equal, the neutral carries what is left over.
The tool works that left-over current as a phasor sum. It sets phase A at 0°, phase B at −120° and phase C at +120°. It then turns each current back by its own power factor angle, because a lagging load draws its current after its voltage. The three currents are added as vectors, and the size of the sum is the neutral current. The tool also gives the angle of the sum from the phase A voltage.
When all three power factors are the same, the angles cancel out of the sum. The tool then shows the short formula: the square root of the sum of the three squares, less the three products of pairs.
The neutral can carry more than the largest phase. That happens when the power factors differ a lot, so two currents line up. The tool warns when it does.
The answer is the current at the supply frequency only. Third harmonic currents from electronic loads add in the neutral, not cancel. The harmonics tool works those.
| Step | Table or clause | What it decides |
|---|---|---|
| Phasor of each phase | The phase angle less the power factor angle | Where each current points |
| Neutral current | The phasor sum of the three | The current the neutral carries |
| One power factor | I_N = √(Ia² + Ib² + Ic² − Ia·Ib − Ib·Ic − Ic·Ia) | The short form of the sum |
| Neutral size | Cl 3.5.2(b)(ii) | A neutral at least the size of the largest active |
| A smaller neutral | Cl 3.5.2 Exception 3 | Allowed for a mostly multiphase load that still carries the out-of-balance current |
| Harmonics | Cl 3.5.2(b)(i) | Third harmonic currents add to the out-of-balance current |
Worked examples
- A shop board with 45, 30 and 25 A on its phases has 18.03 A in the neutral, 40.1 % of the largest phase.
- A farm supply with 40 A on one phase and 5 A on the others has 35 A in the neutral, 87.5 % of the largest phase. Nearly all of the load comes back on it.
- Heaters on phase A and a motor on phase B at 0.8 power factor give 19.69 A in the neutral, 65.6 % of the largest phase.
- A mostly three‑phase load of 60, 55 and 50 A at 0.85 power factor leaves 8.66 A in the neutral, 14.4 % of the largest phase.
Limits
The tool takes three phase currents and their power factors, all lagging. It does not take a leading load, such as a capacitor bank, or a load connected between two phases.
It gives the current, not the conductor size. Take the larger of the neutral current and the largest phase current to the cable size tool.
See also: Three phase power, Max demand by phase and Cable size.
Pātai
He āwhina hoahoa te hua. Manatokohia ki te paerewa o nāianei.
Me pēhea te tātai i te iahiko neutral o tētahi uta wāhanga toru?
Tāpirihia ngā iahiko wāhanga toru hei phasors, 120° te wehe, ia tētahi e huri ana e tōna koki power factor. Ko te rahi o te tapeke ko te iahiko neutral. Ina kotahi te power factor mō ngā wāhanga katoa ko te √(Ia² + Ib² + Ic² − Ia·Ib − Ib·Ic − Ic·Ia).
He aha te Iahiko Neutral kāore he rerekētanga i waenga i ngā wāhanga?
Ka rerekē ngā iahiko wāhanga e 120°, nō reira kāore e tāpiri, e tango i te rārangi tōtika. 32 A, 20 A me 10 A ka hoatu 19.08 A i te neutral, kāore i te 22 A, kāore i te 12 A.
Ka taea e te neutral te kawe neke atu i tētahi wāhanga?
Āe. Ina rerekē rawa ngā power factor, ka taea e ngā phasor te rārangi ōrite, ā, ka taea e te neutral te kawe i tētahi nui ake i te wāhanga nui rawa. Ka tāpiri hoki ngā iahiko harmonic tuatoru mai i ngā uta ā-hiko ki te neutral. Ka whakatūpato te taputapu ina nui atu te tapeke i te wāhanga nui rawa.
He rahi pēhea me whai te neutral o tētahi ara iahiko wāhanga toru?
E tono ana AS/NZS 3000 Cl 3.5.2(b)(ii) mō tētahi neutral he rahi ōrite ki te active nui rawa. Ka whakaaetia e Exception 3 tētahi he iti ake ina he wāhanga maha te nuinga o te uta, ā, ka kawe tonu te neutral i te iahiko kore taurite me ōna harmonics.
Me whai neutral te uta taurite?
Ka whakakore ngā iahiko ōrite e toru i tētahi power factor kotahi, nā reira kāore he iahiko neutral i te taumata tuatahi. Ka hiahia tonu te uta whetū me ngā taonga wāhanga kotahi, nā te mea ka rerekē te taurite ina wetekia tētahi uta.
Ngā Clause me ngā Table e pānuitia ana e tēnei taputapu
- AS/NZS 3000:2018 Cl 3.5.2(b)Neutral of a multiphase circuit
- AS/NZS 3000:2018 Cl 3.5.2Neutral conductor of a circuit
Ia Clause me Table, me te pēhea i manatokotia ai ia tētahi
Ngā tūtohi i arotakehia whakamutunga i te 2 Oct 2026.
Ngā taputapu hononga
- Tātaitai rahi tauraFind the smallest cable size that passes each check.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- Voltage unbalance o tētahi puna hikoVoltage or current unbalance from three line readings.Kāore he paerewa
- Harmonics, Iahiko Neutral me te k factorTHD, neutral current and K-factor from a spectrum.AS/NZS 3008.1AS/NZS 3000
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