Solar DC Cable Sizing Calculator

Most residential rooftop solar systems in Australia use 4mm² or 6mm² cross-linked polyethylene (XLPE) double-insulated copper solar cable. The correct size depends on the total cable run length and the system current, ensuring that the total voltage drop is kept below the 3% limit.

AS/NZS 5033 strictly limits the voltage drop on the DC side of a solar PV installation to a maximum of 3% measured from the PV array to the input terminals of the inverter. Sizing cables correctly is critical to prevent power losses and electrical heating.

Yes, in most standard residential rooftop setups, a 4mm² DC solar cable is compliant if the one-way cable run from the solar panels to the inverter is less than 20 to 25 metres. For runs longer than 25 metres, upgrading to 6mm² cable is typically required to stay under the 3% voltage drop limit.

Voltage drop is calculated using the formula: Voltage Drop (V) = Current (Isc) × Conductor Resistance (Ω/km) × Total Loop Cable Length (km). Total Loop Length is twice the one-way distance (positive + negative run). The percentage drop is: (Voltage Drop V ÷ Voc) × 100.

A 6mm² copper cable has a larger cross-sectional area and a lower DC resistance (~3.93 Ω/km) compared to a 4mm² cable (~5.88 Ω/km). This lower resistance results in less voltage drop and power loss, making 6mm² ideal for high-current strings or long wiring runs.

Yes. Solar DC wiring on rooftops is exposed to extreme temperatures and UV radiation. Under AS/NZS 5033, you must use double-insulated, UV-resistant, flexible copper cables specifically rated to standard EN 50618 (often marked as H1Z2Z2-K or PV1-F).

For a typical 10A string at 400V, a 4mm² DC cable can be run approximately 30 metres before exceeding the 3% voltage drop threshold. For higher current panels (e.g. 13A or 14A), the maximum compliant distance drops to around 20 to 22 metres.

High ambient temperatures on metal roofs increase conductor resistance. While basic voltage drop calculations use resistance at 75°C, AS/NZS 5033 also requires checking the cable's current-carrying capacity under roof-space temperature conditions, which can exceed 65°C.

Under AS/NZS 5033 guidelines, voltage drop sizing and current-carrying capacity calculations are conducted using the short-circuit current (Isc) of the PV array rather than the maximum power current (Imp) to design for the worst-case operating scenario.

No. Solar DC conductors must be segregated from AC mains cabling to prevent high-voltage DC faults from entering AC distribution boards. Under AS/NZS 3000, they must run in separate conduits or be separated by a compliant barrier.

The Clean Energy Council (CEC) enforces strict compliance with AS/NZS 5033. Installers must calculate and document DC voltage drop for every job. Sizing must be designed to ensure maximum system efficiency and absolute electrical safety.

String inverters have long DC runs from the roof to the inverter, requiring careful calculation using this tool. Microinverter systems convert DC to AC directly on the back of each panel, meaning the DC runs are short factory leads, and you size the AC trunk cable instead.

Undersized cables create high electrical resistance, causing power to be wasted as heat. This reduces the system's energy yield, lowers your feed-in tariff return, and can lead to dangerous thermal hotspots, melting insulation, or electrical fires.

No. The positive and negative conductors in a solar string run side-by-side and have the same current flowing through them, so they must be sized identically. The loop calculation automatically accounts for the combined resistance of both conductors.

The formula is: Vd = Isc × 2 × L × Rc / 1000, where Isc is the short-circuit current, L is the one-way distance in metres, and Rc is the conductor DC resistance in Ω/km. Percentage drop is then: Vd_pct = (Vd / Voc) × 100.