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AS/NZS 3000-2018 AS/NZS 3008.1.1-2017
Voltage Drop — More Than a Compliance Issue
Voltage drop in solar wiring is not just a compliance issue — every volt dropped in the DC cables is a volt that the inverter cannot convert to AC power. Over 25 years of operation, a 3% voltage drop in the DC wiring means approximately 3% less energy production — thousands of kWh lost on a residential system. Good cable design pays for itself through improved yield.
AS 3000 Voltage Drop Limits
Circuit Type | Max Permitted Voltage Drop | Notes |
|---|---|---|
AC supply circuit (switchboard to load) | 5% of supply voltage (11.5 V for 230 V) | Per AS 3000 Cl. 3.6.2 |
Solar AC inverter output to switchboard | 5% total (shared with other circuit drops) | Recommend <2% on solar AC leg alone |
DC string cables | Not specified in AS 3000 — industry best practice | Best practice: <1% per string; <3% total DC circuit |
DC Voltage Drop Calculation Example
String: 14 panels × 37.5 V = 525 V VOC. Operating current IMP = 11.3 A. Cable run: 18 m from array to inverter. Cable: 6 mm² copper.
Vdrop = (2 × 18 × 11.3 × 0.0225) / 6 = 1.53 V
Percentage = 1.53 / (14 × 36 VMP) = 1.53 / 504 = 0.3% — excellent
When to Upsize Cables for Yield, Not Just Compliance
For commercial systems where DC cable runs exceed 50 m, a detailed financial analysis of upsizing cables is worthwhile:
Moving from 6 mm² to 10 mm² DC cable reduces voltage drop by 40%
On a 100 kW system with 2% DC cable losses, this saves approximately 400 kWh per year
At $0.10/kWh wholesale value over 25 years with 5% discount rate, the additional cable cost can pay back within 5 years
Engr. Jason Morales — Founder, SolarEnergyPH
