现有回路检查
检查已安装回路：电缆、保护装置、电压降和 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.
尝试一个工程 7
每项工作都会预填示例数值。请替换为您自己的数值。
- 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.
输入
使用默认输入值的示例计算。
- 相
- 单相
- 电压
- 230 V
- 设计电流
- 20 A
- 功率因数
- 0.9
- 标准
- NZ · AS/NZS 3008.1.2
- 敷设长度
- 30 m
- 敷设方式
- 在空气中封闭敷设
- 环境温度
- 30 °C
- 成组回路
- 1
- 已安装电缆规格
- 2.5 mm²
- 材料
- 铜
- 绝缘
- PVC 75 °C
- 芯线
- 多芯
- 并联电缆
- 1
- 电压降限值
- 5 %
- 外部阻抗 Ze
- 0.35 Ω
- 预期短路电流
- 0 kA
- 装置曲线
- C 型曲线
- 保护装置额定值
- 20 A
2.5 mm² 回路
通过
- 修正后载流量 Iz
- 23A
- 电压降
- 4.25%
- 接地故障回路阻抗
- 0.89Ω
- 装置的最大 Zs
- 1.53Ω
- 通过校核的最小规格
- 2.5mm²
- 电缆允许的最大 C 曲线装置
- 20A
- 综合修正系数
- ×1.00
此结果仅供设计参考。请对照现行标准进行核验。
计算步骤
- 已安装导体规格2.5mm²
AS/NZS 3008.1.2:2017 Table 13 p.62–64
- 2.5 mm² 的表列额定值23A
AS/NZS 3008.1.2:2017 Table 13 p.62–64
- 环境温度修正系数×1.00
AS/NZS 3008.1.2:2017 Tables 27(1), 27(2) p.88
- 成组修正系数×1.00
One circuit, no grouping factor
- 综合修正系数×1.00
- 修正后的额定值 Iz23A
AS/NZS 3000:2018 Cl 3.4
- 电压降9.78V
- 电压降百分比4.25%
AS/NZS 3000:2018 Cl 3.6.2
- 装置额定值 In20A
AS/NZS 3000:2018 Cl 2.5.3.1
- 接地导体规格2.5mm²
AS/NZS 3000:2018 Table 5.1
- 相对地 230 V 时的接地故障回路阻抗0.89Ω
AS/NZS 3000:2018 Table 8.1
- 该装置允许的最大 Zs1.53Ω
AS/NZS 3000:2018 Table 8.1
- 符合要求的最小规格2.5mm²
AS/NZS 3000:2018 Cl 3.4
关于此计算器
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.
问题
结果仅供设计参考。请依据现行标准核对。
4 mm² 电缆可以配多大的断路器？
这取决于敷设方式。单独穿管敷设于 30 °C 空气中时，新西兰的 4 mm² 铜导体额定为 29 A，因此 25 A 断路器为最大标准规格。成组、发热或绝缘会降低该值。输入您的敷设方式，即可查得电缆允许的最大断路器规格。
Ib ≤ In ≤ Iz 是什么意思？
Ib 为负荷的设计电流，In 为断路器额定值，Iz 为修正后的电缆载流量。断路器须能承载负荷，电缆须能承载断路器额定值。该规则见 AS/NZS 3000 Clause 2.5.3.1。
为何长回路在回路阻抗上不合格？
长距离或小截面电缆的接地故障回路阻抗较高。此时故障电流过低，无法及时使断路器按其瞬时整定值动作。请使用较大截面电缆、较低额定值的断路器、B 型曲线，或核查该回路的 RCD 规则。
本工具是否测量我的回路？
否。它依据电缆截面、线路及您输入的外部阻抗 Ze 计算。请在现场测量 Ze 和 Zs，并将读数与工具给出的最大 Zs 进行比较。
回路不合格时，工具建议多大的截面？
在相同的断路器、路径和负荷下，能通过全部检查的最小标准截面。这也是电缆截面计算器对同一回路给出的结果。
计算示例
- 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.
背景
本工具读取的条款和表格
- 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
表格最后核对于 27 Sept 2026。
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有问题，或数值看起来有误？联系我们。