AC Voltage Rise Calculator
Inverter to point of supply, checked against the AS/NZS 4777.1 2% limit.
Inverter
Leave blank to work it out from the rating (kVA / 230 V, or kVA / (1.73 x 400 V) for three phase). More than one inverter: check each one's path with its own rating, and enter the combined current on the cables they share (Clause 3.4.1).
If set, the consumer mains rise uses the export-limited current when it's lower (Clause 3.3.3 (c)). Cable capacity is always checked against the full current, never the export limit (Clause 3.3.1).
Every cable that carries the inverter's current, in order. The rises add up against one 2% limit, the same way volt drop does - each one worked out with the Mains & Submain Cable Selection method.
Multicore 1 to 10 mm² is rated as PVC (75°C); 16 mm² and up as XLPE (90°C). For typical New Zealand installation conditions only. Based on 30°C ambient air temperature, 15°C ambient soil temperature and 1.2°C.m/W thermal resistivity.
For guidance only. These calculators are planning aids for licensed electrical workers and inspectors. All results must be independently verified against the current editions of AS/NZS 3000:2018, AS/NZS 3008.1.2, and other applicable standards before being relied on for any installation. CertMate accepts no responsibility or liability for any work carried out, decisions made, or certification issued in reliance on these results. The certifying electrical worker remains solely responsible for compliance with the Electricity (Safety) Regulations 2010 and all applicable New Zealand law.
Volt drop in reverse
When an inverter exports, current flows from the inverter back out to the grid, so the voltage at the inverter is higher than at the point of supply. AS/NZS 4777.1 keeps that rise to 2% across every cable in the path - the inverter cable, any submains and the consumer mains - on top of the usual AS/NZS 3000 volt drop limit.
This calculator works each cable out with the same cable-by-installation-condition method as the Mains & Submain Cable Selection calculator, adds them up against the 2% limit, and checks every cable's capacity against the inverter's full rated current, which an export limit can't reduce.
Worked example
5 kVA inverter, 20 m from the switchboard
The example AS/NZS 4777.1 itself works through: a single-phase 5 kVA inverter (21.74 A), 15 m of 16 mm² consumer mains and a 20 m inverter cable. On 4 mm² the total rise is over 2%; 6 mm² brings it back within the limit. With multicore inverter cable partly surrounded by insulation and buried consumer mains, this calculator gives about 2.35% and 1.63% - a little under the standard's simplified table method (2.5% and 1.8%), which assumes every cable is at its full rated temperature, but the same answer: 6 mm².
Frequently asked questions
What is the voltage rise limit for solar inverters in New Zealand?
AS/NZS 4777.1 limits the voltage rise from the point of supply from the grid to the inverter's a.c. terminals to 2% of the nominal voltage at the point of supply - 4.6 V on a 230 V single-phase supply, 8 V on a 400 V three-phase supply. It applies on top of the AS/NZS 3000 volt drop limit.
Which current do I use for voltage rise?
The inverter's rated current. Where an export or generation limit caps the current on a cable, AS/NZS 4777.1 allows that limited current to be used for that cable's rise - typically the consumer mains under a site export limit.
Can an export limit let me use a smaller cable?
Only for the voltage rise. Every cable carrying inverter current must still have a current-carrying capacity of at least the inverter's full rated current - AS/NZS 4777.1 doesn't allow an export or generation limit to be used for cable capacity.
Why is voltage rise important?
When the inverter exports, the voltage at its terminals sits above the grid voltage by the rise in the cables. Too much rise pushes voltages up inside the installation and can trip the inverter on over-voltage, so it stops generating exactly when it should be producing most.
Related calculators
CertMate creates your CoCs, ESCs and solar test sheets in minutes, on any device, on site.
Start Free Trial