MCB trip curve at cable limit
I-plot ang MCB trip band laban sa cable na pinoprotektahan 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 2 Oct 2026.
Subukan ang isang job 4
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Check a breaker clears a long circuitA long lighting run with little fault current against its breaker and cable.
- See a D curve on a motor circuitHow long a D curve breaker can take at a modest fault, against the cable.
- Check a small cable near the boardWhether a high fault current outruns a small cable before the breaker trips.
- Compare a B and C curve breakerThe instant trip current of a Type B breaker on a socket‑outlet circuit.
Mga input
Worked example gamit ang mga default na input.
- Uri ng breaker
- Curve C
- Rating
- 20 A
- Fault current sa malayong dulo
- 300 A
- Fault current sa board
- 0 A
- Standard
- NZ · AS/NZS 3008.1.2
- Cable size
- 2.5 mm²
- Material
- Tanso
- Insulation
- PVC 75 °C
Pinakahuling trip sa fault current
0.1s
- Kakayahang tumagal ng cable sa fault current
- 0.86s
- Instant trip, batayan ng Table 8.1
- 150A
- Instant trip, karaniwang saklaw
- 100 hanggang 200A
- Conventional operating current
- 29A
- Pinakamalaking Zs para sa 0.4 s
- 1.53Ω
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Conventional operating current29A
AS/NZS 3000:2018 Cl 2.5.3.1
- Mean tripping current, Type C150A
AS/NZS 3000:2018 Table 8.1
- Instantaneous trip sa mean, hindi lalampas sa0.1s
AS/NZS 3000:2018 Table 8.1
- Pinakamalaking Zs para sa 0.4 s1.53Ω
AS/NZS 3000:2018 Table 8.1
- Karaniwang instantaneous band, mababang gilid100A
- Karaniwang instantaneous band, mataas na gilid200A
- k factor×111.00
AS/NZS 3008.1.2:2017 Table 52 p.121
- Kakayahang tumagal ng cable sa fault current0.86s
AS/NZS 3008.1.2:2017 Cl 5.3
- Pinakahuling trip sa fault currentResulta0.1s
Tungkol sa calculator na ito
How this is calculated
A miniature circuit-breaker does not trip at one exact time for a current. Two breakers of the same type and rating trip at different times, so a maker draws a band: the earliest and the latest each can trip. This tool draws that band for a Type B, C or D breaker, draws the cable's limit beside it, and reads the latest trip time at the fault current you enter.
Three figures come from AS/NZS 3000. A breaker operates within its conventional time at 1.45 times its rating. Table 8.1 takes it as tripping instantly, within 0.1 s, at its mean tripping current: 4 times the rating for Type B, 7.5 for Type C and 12.5 for Type D. The largest loop impedance for a 0.4 s disconnection follows from that current. The rest of the band, the edges of the instant region and the thermal part, is a typical band. AmpSize does not hold AS/NZS 60898, and the result says so.
The cable's line is its adiabatic limit: the time it can carry a fault current before its insulation is damaged, from the k factor of AS/NZS 3008.1, through the fault rating tool. The circuit passes when the breaker's latest time is no longer than the cable's time at that current. Check it at the far end, where the fault current is least and the trip slowest, and give the fault current at the board too: there the current is highest, the cable's time shortest, and the worse of the two ends decides.
| Step | Table or clause | What it decides |
|---|---|---|
| Conventional operating current | AS/NZS 3000 Cl 2.5.3.1 | Where the band starts |
| Instant trip at the mean current | AS/NZS 3000 Table 8.1 and Para B4.5 | The current that trips it instantly, and the largest Zs |
| Instant region and thermal edges | A typical band, not a standard | The earliest and latest trip at each current |
| The cable's limit | AS/NZS 3008.1 Table 52 and Cl 5.3 | The time the cable withstands the fault |
| The check | The latest trip against the cable's time | Whether the breaker clears the fault first |
Worked examples
- A C20 lighting circuit in 2.5 mm² with a 300 A fault trips in 0.1 s at the latest, well inside the cable's 0.86 s. The Table 8.1 instant trip current is 150 A.
- A B20 circuit in 2.5 mm² with a 150 A fault trips in 0.1 s against the cable's 3.42 s. The Table 8.1 instant trip current is 80 A.
- A D32 motor circuit in 6 mm² with a 500 A fault can take up to 1.6 s on the slow edge of the band, just inside the cable's 1.77 s. Table 8.1 counts it as instant above 400 A.
- A long B16 circuit in 1.5 mm² with only 60 A of fault current fails: the breaker can take 27.74 s, longer than the cable's 7.7 s, and 60 A is under the Table 8.1 instant trip current of 64 A.
- The same C20 circuit with 3000 A of fault at the board fails at the board: the band shows 0.1 s there, and the cable lasts 0.01 s at 3000 A, though it takes 0.86 s at the far end's 300 A. The maker's let-through energy decides it.
- A C32 circuit in 4 mm² close to the board, 2000 A of fault fails on the band: it shows 0.1 s, and the cable lasts 0.05 s. The maker's let-through energy decides it.
Limits
The band is typical, not a maker's curve. A real breaker clears a large fault in much less than 0.1 s, and limits the energy it lets through; the maker publishes that energy as I²t. Where the band fails a cable at a high current, compare the maker's I²t with k²S² before you change the cable.
gG fuses are not drawn yet. Their curves are in IEC 60269, which AmpSize does not hold.
See also: Loop impedance, Fault rating and IDMT protection.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Ano ang pagkakaiba ng B, C at D curve na MCB?
Gaano karaming current ang nagti-trip nito agad. Kinukuha ng AS/NZS 3000 Table 8.1 ang mean bilang 4 na beses ng rating para sa Type B, 7.5 para sa Type C, at 12.5 para sa Type D. Ang mas mataas na type ay nakakaraos sa motor at transformer start.
Bakit iginuguhit bilang band ang trip curve?
Dalawang breaker na magkapareho ang type at rating ay nagti-trip sa magkaibang oras. Ipinapakita ng maker ang pinakamaaga at pinakahuling oras na maaaring mag-trip ang bawat isa. Binabasa ng tool ang pinakahuling oras, kaya nananatiling totoo ang check para sa pinakamabagal na breaker.
Paano ko malalaman kung pinoprotektahan ng breaker ang cable sa fault?
Kayang dalhin ng cable ang fault current sa loob ng oras na itinatakda ng k factor at laki nito, (k × S ÷ I)². Dapat mag-trip ang breaker sa loob ng oras na iyon. Ikinukumpara ng tool ang dalawa sa fault current na ilalagay mo.
Curve ba ng maker ang band?
Hindi. Galing sa AS/NZS 3000 ang operating point, at karaniwan para sa type ang mga gilid ng band. Walang hawak na AS/NZS 60898 ang AmpSize. Tingnan sa curve ng maker ang malapit na resulta.
Paano kung mas maikli sa 0.1 s ang kayang itagal ng cable?
Malapit sa board, mataas ang fault current at ilang millisecond lang tumatagal ang maliit na cable. Naaalis ng breaker ang malaking fault nang mas mabilis sa 0.1 s. Ikumpara ang let-through energy ng maker, I²t, sa k²S².
Mga clause at table na binabasa ng tool na ito
- AS/NZS 3000:2018 Cl 2.5.3.1Operating points of circuit-breakers and fuses
- AS/NZS 3000:2018 Table 8.1Maximum earth fault loop impedance multipliers by MCB curve
- 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 2 Oct 2026.
Mga kaugnay na tool
- Earth fault loop impedance calculatorCheck earth fault loop impedance against the maximum Zs.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- Transformer inrush at ang breaker nitoCheck a transformer’s switch-on inrush against its breaker.AS/NZS 3000
- Cable fault rating calculatorCheck that a conductor can withstand the fault current.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
Nakatulong ba ito?
May tanong, o may value na mukhang mali? Makipag-ugnayan sa amin.