Công cụ tính cầu dao cách ly và nối đất PV

How this is calculated#

The tool completes the PV string tool. It takes the module Isc, the strings and the array maximum voltage. It gives the cable currents, the d.c. isolator ratings, the enclosure and the earthing. It reads AS/NZS 5033:2021.

1. String current. It works 1.25 × KI × Isc (Cl 3.3.3.1). Each string can also take fault current from the other strings (Cl 3.3.3.2).
2. Cable currents. It gives the string, sub-array and array cable currents (Table 4.2).
3. Protection. If you enter a sub-array or array protective device, it checks the rating against the strings it covers (Table 3.1).
4. Isolator voltage and current. The voltage rating is at least the array maximum voltage (Cl 4.3.4.1). Ithe is read at 40 °C indoors or in the shade, and at 60 °C outdoors in the sun (Cl 4.3.4.2.3).
5. Make and break. A non‑separated inverter, or a functionally earthed array, needs each pole to break the full current (Table 4.3). A separated inverter lets the poles in series share it (Table 4.4).
6. Enclosure. It gives the enclosure rule (Table 4.5). Outdoors, it adds the pressure-equalisation valve (Cl 4.4.6.2).
7. Earthing. Above 35 V it reads Figure 4.13 and the Table 4.6 columns. It takes the earth size from AS/NZS 3000 Table 5.1, and never less than 4 mm². It adds the 0.5 Ω limit (Cl 4.6.5).
8. Earth faults. A direct functionally earthed array gets an interrupter setting (Table 3.2). The tool adds an earth fault alarm above 120 V, or for a non‑separated inverter (Cl 3.5.3).

Worked example#

• 4 unfused strings of 13.9 A modules, 450 V, non‑separated inverter. The string current is 17.38 A. The string cable carries 52.13 A and the array cable carries 69.5 A. The isolator sits at the array in the sun, so Ithe is read at 60 °C and must be at least 69.5 A at 450 V. Ie must be at least 69.5 A. Each pole must break 69.5 A. The earth is 4 mm².

Limits#

• The tool does not size cables. It gives each current. Use the DC cable size calculator for the conductor.
• The 1.25 factor and the 4 mm² least conductor come from the PV string limits. The tool derives them from the text of AS/NZS 5033 until the Standard is checked.
• The maker's data sheet governs the isolator. Enter its Ithe, Ie and make and break figures to run the checks.
• The array maximum voltage comes from the PV string tool. Run that tool first.

See also: DC isolator rating for a 10 kW solar array, PV array isolators and earthing, PV string calculator and DC cable size calculator.