PV isolator and earthing calculator
Rate the PV array cables, d.c. isolator and earthing.
Reads AS/NZS 3000:2018 and AS/NZS 5033:2021. Tables checked 1 Oct 2026.
Try a job 4
Each job fills in example values. Replace them with your values.
- Rate the d.c. isolator for a solar arrayCheck an isolator data sheet against two strings at 520 V in the sun.
- Size the earth for a PV array frameThe frame earth for a powered-neutral inverter on 6 mm² array cable.
- Find the currents in a commercial arrayString, sub-array and array currents for 12 strings in three fused sub-arrays.
- Set the earth fault interrupterThe detection setting for a 60 kW array with direct functional earthing.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Module Isc
- 13.9 A
- KI, bifacial factor
- 1
- Strings in parallel
- 4
- Strings per sub-array
- 0
- Array maximum voltage
- 450 V
- Array power
- 0 kW
- Backfeed current from the inverter
- 0 A
- String fuse rating
- 0 A
- Array protection rating
- 0 A
- Inverter
- Non-separated (transformerless)
- Functional earthing of the array
- None
- Isolator on
- The array cable
- Isolator location
- Outdoors, in the sun
- Isolator voltage rating
- 0 V
- Isolator Ithe at the ambient
- 0 A
- Isolator Ie, poles in series
- 0 A
- Isolator make and break current
- 0 A
- Disconnection device
- Switch-disconnector
- Enclosure
- Dedicated, one switch
- Enclosure outdoors
- Yes
- Connected to an earth referenced system
- Yes
- Frame earthed for lightning protection
- No
- Array cable size
- Not entered
- Inverter a.c. cable size
- 6 mm²
d.c. isolator Ithe at 60 °C, at least
69.5 A at 450 V
- String cable current
- 52.13A
- Array cable current
- 69.5A
- Isolator Ie, poles in series, at least
- 69.5A
- Earth conductor, at least
- 4mm²
This result is a design aid. Verify it against the current standard.
Calculation steps
- Maximum string current, 1.25 × KI × Isc17.38A
AS/NZS 5033:2021 Cl 3.3.3.1
- Fault current from the other strings, (SA − 1) × ISTRING MAX52.13A
AS/NZS 5033:2021 Cl 3.3.3.2
- String cable current52.13A
AS/NZS 5033:2021 Table 4.2
- Array cable current69.5A
AS/NZS 5033:2021 Table 4.2
- Isolator voltage rating, at least the maximum voltage450V
AS/NZS 5033:2021 Cl 4.3.4.1
- Isolator Ithe at the operating ambient, at least69.5A
AS/NZS 5033:2021 Cl 4.3.4.2.3
- Operating ambient Ithe is de-rated for60°C
AS/NZS 5033:2021 Cl 4.3.4.2.3(a)(iii)
- Isolator Ie, poles in series, at least69.5A
AS/NZS 5033:2021 Table 4.3
- I(make) and Ic(break) of each pole, at least69.5A
AS/NZS 5033:2021 Table 4.3
- Earth from the table2.5mm²
AS/NZS 3000:2018 Table 5.1
- Earth or bonding conductor, copper, at least4mm²
AS/NZS 5033:2021 Table 4.6
About this calculator
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.
- 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).
- Cable currents. It gives the string, sub-array and array cable currents (Table 4.2).
- Protection. If you enter a sub-array or array protective device, it checks the rating against the strings it covers (Table 3.1).
- 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).
- 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).
- Enclosure. It gives the enclosure rule (Table 4.5). Outdoors, it adds the pressure-equalisation valve (Cl 4.4.6.2).
- 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).
- 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).
| Step | Table or clause | What it decides |
|---|---|---|
| String current | Cl 3.3.3.1 and Cl 3.3.3.2 | The current of one string and its fault share |
| Cable currents | Table 4.2 | The current in the string, sub-array and array cable |
| Protection | Table 3.1 | The least rating of sub-array and array protection |
| Isolator rating | Cl 4.3.4.1 and Cl 4.3.4.2.3 | The voltage and the Ithe |
| Make and break | Table 4.3 and Table 4.4 | The current each pole, or the poles in series, must break |
| Enclosure | Table 4.5 and Cl 4.4.6.2 | The enclosure type and the valve |
| Earth conductor | Figure 4.13 and Table 4.6 | The frame earth or bonding conductor |
| Earth faults | Table 3.2 and Cl 3.5.3 | The interrupter setting and the alarm |
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.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What current does a PV array cable carry?
AS/NZS 5033 Table 4.2 sets it. A string with no fuse carries the fault current the other strings can feed, plus the nearest protection downstream or the backfeed. The array cable carries every string at 1.25 times Isc.
How do I rate a d.c. isolator for a solar array?
Check four figures at the array maximum voltage: the voltage rating, Ithe at 40 °C or 60 °C in the sun, Ie with the poles in series, and the make and break current. A transformerless inverter needs each pole to break the full current.
What size earth does a PV array frame need?
Follow Figure 4.13 of AS/NZS 5033. Lightning protection takes 16 mm². Otherwise the inverter type and the d.c. protection pick a column of Table 4.6. The least size for the frames is 4 mm².
Does the tool size the d.c. cables?
No. It gives the current each cable must carry. Size each cable with the d.c. cable size tool at that current, at least 4 mm², at the hot cable temperature near the modules.
When is an earth fault alarm needed?
AS/NZS 5033 Cl 3.5.3 calls for one above 120 V, or with a non-separated inverter. A directly earthed array also needs an earth fault interrupter set by Table 3.2 from the array power.
Clauses and tables this tool reads
- AS/NZS 5033:2021 Cl 3.3.3.2Fault current from parallel strings
- AS/NZS 5033:2021 Cl 3.5.3Earth fault alarm
- AS/NZS 5033:2021 Cl 4.3.4.1PV isolator voltage rating
- AS/NZS 5033:2021 Cl 4.3.4.2.3Ratings of a PV d.c. switch-disconnector
- AS/NZS 5033:2021 Cl 4.4.2.2PV cable temperature
- AS/NZS 5033:2021 Cl 4.4.6.2Outdoor enclosure pressure equalization
- AS/NZS 5033:2021 Cl 4.6.5Frame earth resistance
- AS/NZS 5033:2021 Figure 4.13Frame earthing conductor
Every clause and table, with how each was verified
Tables last checked on 1 Oct 2026.
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