Why does a single-phase inverter on a three-phase cable use the factor of 2?

Its current flows out on one active and back on the neutral, just as on a single-phase circuit, so √3 does not apply. This assumes the neutral is the same size and material as the active.

Does it size the cable for current-carrying capacity?

No. Current-carrying capacity depends on install method, cable grouping, insulation and ambient temperature, and must be checked against the AS/NZS 3008.1 tables. This tool does not reproduce those tables.

Which resistivity does it use?

Without an entered Vc it uses the same disclosed copper and aluminium resistivity as the voltage drop calculator, set out in the method. It ignores reactance and conductor temperature rise, so it is likely to understate the rise at operating temperature.

Design Worksheet

AC Voltage Rise Budget

Chain the AC cable segments from the inverter to the point of supply, estimate each segment's voltage rise at the inverter's rated output current, and compare the total with a budget you enter.

Sources listedReviewed September 2026Our methodology

Inputs

View result

Inverter AC outputOne inverter's current is single-phase or three-phase all the way to the point of supply, so this sets the basis for every segment.

Rated AC output currentFrom the inverter datasheet.

Nominal voltage (phase-to-neutral)Enter the phase-to-neutral nominal voltage for this supply. Percentages use it as the denominator.

Segment 1

Segment name

One-way length

Conductor cross-section

Conductor material

Circuit arrangementOut on the active and back on the neutral: factor of 2.

Vc from your copy of AS/NZS 3008.1 (optional)Use the single-phase value for this cable, including a three-phase cable carrying the inverter on one active. When entered, rise = Vc × I × L ÷ 1000 and the resistivity estimate is not used.

Your rise budgetOptional. Enter the budget your design works to. Wattbench does not supply one.

Budget unit

Take the budget from AS/NZS 4777.1 and your network service provider's connection rules.

Live result

Edit inputs

Estimated total rise

–V

Of nominal voltage

–%

Enter the inverter current, the nominal voltage and each segment's length and conductor to see the estimated rise.

Key takeaways

Works out the estimated voltage rise on each AC cable segment between the inverter and the point of supply, adds them up and names the segment contributing the most.
Single-phase segments use a factor of 2 and balanced three-phase segments use √3 with line current. A single-phase inverter on a three-phase cable still uses the factor of 2, because its current flows on one active and the neutral.
Without a Vc from AS/NZS 3008.1 each segment is resistance-only near 20 °C and ignores reactance, so it is likely understated at operating temperature.
Wattbench does not supply a rise budget. You enter your own from AS/NZS 4777.1 and the network's connection rules, and the result reads as within or over that entered budget, not as a compliance verdict.
Naming a segment to upsize is not a current-carrying-capacity check. Confirm the conductor's rating against the AS/NZS 3008.1 tables.

How it works

Each segment is one cable run between the inverter and the point of supply, worked at the inverter's rated AC output current and added together:

Single-phase segment: V rise = (2 × length × current × ρ) ÷ area, where the factor of 2 covers the active and the neutral, and ρ is conductor resistivity (~0.0175 Ω·mm²/m for copper, ~0.0282 for aluminium, near 20 °C). The percentage uses the phase-to-neutral nominal voltage you enter.
Single-phase inverter on a three-phase cable:the inverter's current still flows out on one active and back on the neutral, so the same factor of 2 applies. This assumes the neutral is the same size and material as the active.
Balanced three-phase segment: V rise = (√3 × length × line current × ρ) ÷ area, a line-to-line figure, so the percentage uses the line-to-line nominal voltage you enter. A chain never mixes the two bases: the inverter's output type sets the basis for every segment.
With a Vc entered from your copy of AS/NZS 3008.1for that segment's circuit arrangement: V rise = Vc × current × length ÷ 1000, with no further factor applied.

Without a Vc, each segment is resistance-only: it ignores reactance and uses resistivity near 20 °C, so it is likely understated at operating temperature. The segment with the largest estimated rise is named as the first to consider upsizing. Upsizing for rise is not a current-carrying-capacity check: confirm the conductor's rating against the AS/NZS 3008.1 tables for the install method, grouping and ambient temperature (this tool does not reproduce them), and have a licensed electrician sign off the final design.

Wattbench does not supply a rise budget. Take yours from AS/NZS 4777.1 and the connection rules of your network service provider, and enter it yourself. The comparison is arithmetic on your inputs, not a compliance result. After installation, record measured readings in the AC Voltage Rise Worksheet.

Estimates only: for guidance, not a quote or a compliance certificate. Verify against the current AS/NZS standards and a licensed design. The maths runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately save the result.

Source ledger2 sources

Standards bodyAS/NZS 3008.1.1:2017 — Standards Australia catalogue
Standards bodyAS/NZS 4777.1:2016 — Standards Australia catalogue

Best next action

AS/NZS 4777.1Do this next AS/NZS 3008.1Standard

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Good to know

Frequently asked

Does Wattbench tell me the allowed voltage rise?: No. The budget field starts empty and the tool never fills it. Take the budget from AS/NZS 4777.1 and your network service provider's connection rules, and enter it yourself.
Why does a single-phase inverter on a three-phase cable use the factor of 2?: Its current flows out on one active and back on the neutral, just as on a single-phase circuit, so √3 does not apply. This assumes the neutral is the same size and material as the active.
Does it size the cable for current-carrying capacity?: No. Current-carrying capacity depends on install method, cable grouping, insulation and ambient temperature, and must be checked against the AS/NZS 3008.1 tables. This tool does not reproduce those tables.
Which resistivity does it use?: Without an entered Vc it uses the same disclosed copper and aluminium resistivity as the voltage drop calculator, set out in the method. It ignores reactance and conductor temperature rise, so it is likely to understate the rise at operating temperature.
Is my data stored or sent anywhere?: The calculation runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately select Save result.

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