Solar DC cable sizing calculator

Use this calculator when a PV DC cable candidate needs a transparent voltage-drop screen before the result is carried into solar design, inverter scheduling, installation planning or estimating review. The page calculates from values entered by the user: PV array current, string voltage basis, one-way route length, candidate cable size, conductor resistance, temperature resistance factor and project target.

The page is deliberately narrow. It does not choose the final solar cable size, assign strings to inverter inputs, check product listings, choose protection, select isolators, complete DNSP connection review or certify installation compliance. It records the arithmetic consequence of the entered candidate so another reviewer can see whether the candidate is worth carrying forward.

PV DC cable candidate use cases

A useful record names the PV run and the source basis. "Solar cable checked" is weak. "PV-STRING-1, 16 mm2 candidate, 18 A, 450 V, 32 m one-way, 1.15 ohm/km, 1.00 factor, 1.325 V drop and 0.29% against an entered 1.5% target" can be reviewed when the string, route or cable data changes.

Solar DC data checklist

The calculator is strongest when the values come from the same project record. A resistance value from a different conductor, temperature basis or cable family can produce a tidy-looking result that does not belong to the actual PV route.

Candidate method matrix

The method is a worksheet, not a selector. If the result is above target, the next action is to review route length, current basis, candidate cable data and project requirements. The calculator does not decide which replacement conductor, product or installation method should be used.

Worked records

These records show why the candidate cable size alone is not enough. A small resistance value can still become material over a long route or high current. A target margin that looks generous on one route can narrow when string voltage, current or temperature basis changes.

Review workflow

1. Identify the PV DC run reference from the array layout, string schedule, inverter input schedule, drawing or site note.
2. Confirm the PV current basis for the route being screened.
3. Enter the string voltage basis used for the voltage-drop percentage.
4. Enter the one-way route length for the positive and negative conductor path.
5. Enter the candidate cable size and the single-conductor resistance from the project cable source.
6. Apply a resistance temperature factor only when the project basis supports it.
7. Enter the voltage-drop target used by the project or reviewer.
8. Read volts, percent, load-side voltage, cable loss and maximum route length together.
9. If the target is exceeded or the margin is narrow, recheck route length, current basis, cable data and PV equipment limits.
10. Move final cable selection, protection, isolator, installation method, product and standards decisions into the relevant project review.

This workflow keeps the page as a calculator-led record. It helps identify whether a candidate deserves more attention, but it does not replace PV design, product data or competent review.

Boundary with neighbouring calculators

Keeping this boundary clear prevents a useful voltage-drop screen from becoming an unsupported PV design approval tool. The output should travel with its assumptions, not as a standalone answer.

Australian context

PV array and cable work in Australia can involve AS/NZS 5033, AS/NZS 3008, AS/NZS 3000, DNSP conditions, equipment listings, product instructions and project documentation. This calculator stays with transparent arithmetic and user-entered values. It does not reproduce protected standards tables, cable ratings, product listings, DNSP approval rules or inverter compatibility data.

The safest public model is to make the source values visible. The user enters current, voltage, route length, conductor resistance, temperature factor and target. The result can then be reviewed beside module data, inverter data, cable schedules, installation conditions, protection records and local authority requirements.

Minimum export record

Stop points

• The PV current basis is unknown or copied from a different string arrangement.
• The string voltage basis is not tied to the module and temperature record.
• Route length excludes roof paths, risers, isolator positions or actual site deviations.
• Conductor resistance comes from another cable size, material or temperature basis.
• The temperature resistance factor is guessed rather than documented.
• The calculated percentage is above the entered target or leaves little margin.
• The result is being used as final PV cable selection without current capacity, protection, isolator, product and installation review.
• DNSP, local authority, manufacturer or current standards requirements are being treated as optional.

The useful output is a repeatable candidate record. Keep the current, voltage, route, resistance source and target together so another reviewer can repeat the result when the PV layout or cable basis changes.