Solar PV Voltage Rise to AS/NZS 4777.1:2024

When a solar PV system injects power into the grid, current flows from the inverter through the installation cables toward the network. This current flowing through the cable impedance raises the voltage at the inverter end above the grid voltage. AS/NZS 4777.1:2024 limits this voltage rise to 2 percent of nominal at the point of common coupling. This guide explains the formula, how it differs from voltage drop, and walks through two worked examples. The Solar PV Sizing Calculator checks voltage rise as part of the system design.

What is voltage rise and why it matters

In a normal installation, load current flows from the grid toward the equipment, causing voltage to drop along the cable. In a solar installation, the inverter generates current that flows in the opposite direction, from the installation back toward the grid. This reverse current flow raises the voltage at the inverter terminals above the grid voltage.

Excessive voltage rise causes problems. Equipment connected to the same circuit sees higher-than-nominal voltage. The inverter may trip on overvoltage protection, reducing energy yield. Neighbours on the same distribution transformer may experience voltage fluctuations as the solar system ramps up and down with cloud cover.

The AS/NZS 4777.1:2024 limit

AS/NZS 4777.1:2024 limits voltage rise caused by the inverter energy system to 2 percent of the nominal voltage at the point of common coupling (PCC). For a 230 V single-phase supply, the limit is 4.6 V. For a 400 V three-phase supply, the limit is 8 V line-to-line.

Some distribution network service providers (DNSPs) allow up to 3 percent on longer distribution feeders, but always check the local connection agreement.

Where voltage rise occurs

Voltage rise accumulates along the cable path from the inverter output to the PCC. In a typical residential installation, this path includes the cable from the inverter to the solar isolator, from the isolator to the switchboard, and from the switchboard to the meter (the PCC). Each segment contributes impedance and voltage rise.

Difference between voltage drop and voltage rise

• Voltage drop: load current flows from grid toward equipment. Voltage decreases. Checked against AS/NZS 3000 Clause 3.6 (5 percent limit).
• Voltage rise: generation current flows from inverter toward grid. Voltage increases. Checked against AS/NZS 4777.1 (2 percent limit).

The formulas are the same; only the direction differs. The Voltage Drop Calculator can be used for both by entering the inverter output current as the design current.

The voltage rise formula

For a single-phase system:

Vrise = I x L x (R x cos(phi) + X x sin(phi))

where I is the inverter output current in amps, L is the one-way cable length in metres divided by 1000, R and X are the cable per-metre resistance and reactance, and cos phi is the inverter power factor (typically 1.0 for modern inverters). For three-phase, multiply by 1.732.

Cable resistance and reactance

Use the same R and X tables from AS/NZS 3008.1.1 as for voltage drop calculations. For typical residential solar cables (4 to 6 mm squared copper PVC), reactance is negligible and the formula simplifies to Vrise = I times L times R. For longer commercial runs on larger cables, include reactance.

Impact on sensitive equipment

When voltage rise pushes the installation voltage above nominal, all equipment on the same circuit sees the elevated voltage. Most equipment tolerates plus or minus 10 percent (207 to 253 V for 230 V), but sustained operation near the upper limit accelerates wear on motors, reduces LED driver lifespan, and may cause electronic equipment to shut down on overvoltage protection.

Mitigation strategies

• Increase cable size: lower R reduces voltage rise proportionally.
• Shorten the cable run: shorter route means less total impedance.
• Reactive power control (Q control): modern inverters can absorb reactive power to reduce voltage at the PCC. AS/NZS 4777.2:2020 mandates volt-VAR and volt-watt response modes.
• Export limiting: cap the inverter output to a level that keeps voltage rise within limits.

Worked example: 6.5 kW residential, 50 m run

A 5 kW single-phase inverter (6.5 kW array) is connected to the switchboard 30 metres from the inverter, and the meter is 20 metres from the switchboard. Total route: 50 metres. Cable: 6 mm squared copper PVC. Power factor: 1.0.

Inverter current at rated output: 5000 / 230 = 21.7 A. R for 6 mm squared at 75 degrees: 3.7 milliohms per metre.

Vrise = 21.7 x 50 / 1000 x 3.7 = 4.01 V

4.01 V is 1.7 percent of 230 V. Under the 2 percent limit. Pass.

Worked example: 30 kW commercial, 200 m run

A 30 kW three-phase inverter is connected 200 metres away via 16 mm squared copper XLPE four-core. Power factor: 1.0.

Inverter current per phase: 30,000 / (1.732 times 400) = 43.3 A. R for 16 mm squared at 90 degrees: 1.38 milliohms per metre.

Vrise per phase = 43.3 x 200 / 1000 x 1.38 = 11.95 V
Vrise line-to-line = 11.95 x 1.732 = 20.70 V

20.70 V is 5.2 percent of 400 V. Exceeds the 2 percent limit (8 V). The cable must be upsized to 35 mm squared or the run shortened.

Common mistakes

• Using the 5 percent voltage drop limit for voltage rise. The voltage rise limit under AS/NZS 4777.1 is 2 percent, not 5 percent.
• Forgetting the meter-to-switchboard cable. The full path from inverter to PCC includes every cable segment.
• Ignoring network impedance. On weak rural networks, upstream impedance is a significant contributor.

Where the calculator fits in

The ElecCalc Solar PV Sizing Calculator includes voltage rise checking. The Cable Sizing Calculator provides R and X values for any cable size.