DC voltage drop calculator

Use this calculator when a general two-wire DC cable run needs a traceable voltage-drop record before the result is carried into a cable schedule, equipment review, site note or estimating worksheet. Typical examples include 12 V and 24 V control supplies, small DC plant, auxiliary DC distribution and low-voltage equipment feeds where the project already has a current, route length and cable data source.

The page is deliberately narrow. It calculates voltage drop, percentage drop, load-side voltage, cable loss and maximum one-way route length at the entered target. It does not select a conductor, choose protection, decide terminals, check product limits, replace a battery cable worksheet, replace a PV string workflow or finalise installation conditions.

Field use cases

A useful record is specific. "DC voltage drop checked" is weak. "DC-CONTROL-1, 20 A, 12 V, 8 m one-way route, 3.3 ohm/km single-conductor resistance, 1.056 V drop and 8.80% against entered 3.0% target" can be reviewed when current, route or cable data changes.

DC data checklist

Low-voltage DC records are source-sensitive. A resistance value from one conductor, temperature basis or installation assumption should not be reused casually for another route. If the source value is complete-circuit mV/A/m, it should already represent the positive and negative conductor circuit. If the source gives single-conductor resistance, the calculator applies a factor of 2 for the two-wire route.

Method comparison matrix

The method is a source judgement, not a convenience choice. If the cable source describes a complete circuit, use circuit mV/A/m. If it describes a single conductor resistance, use resistance mode. If the source is unclear, stop and resolve the source before exporting a record.

Worked records

The examples show why the same cable route can be ordinary in one DC system and material in another. Voltage drop in volts depends on current, length and cable data. Percentage depends on the nominal DC voltage basis. Cable loss in watts adds a separate operating view.

Review workflow

1. Identify the DC run reference from the cable schedule, equipment schedule, drawing or site note.
2. Confirm whether the current is entered directly or calculated from a DC kW basis.
3. Enter the nominal DC voltage used by the project record.
4. Measure or take off the one-way route length for the DC cable run.
5. Select the cable data method and confirm whether the source is single-conductor resistance or complete-circuit mV/A/m.
6. Enter the project voltage-drop target used for comparison.
7. Read voltage drop, percentage, load-side voltage, cable loss and target margin together.
8. If the margin is negative or narrow, recheck route length, conductor data and current basis before changing documentation.
9. Move battery, PV string, fuse, protection, terminals, product settings and installation-condition decisions to the relevant project review.
10. Export the record only when the source values and calculation boundary are clear.

This workflow keeps the calculator as an arithmetic worksheet. It does not decide conductor selection, protection settings, product suitability or installation documentation.

Boundary with AC, battery and PV calculators

Keeping this boundary clear prevents a useful voltage-drop worksheet from becoming a hidden product or installation decision. A competent review can then decide whether the DC route arithmetic is worth carrying forward.

Australian context

DC cable work in Australia can appear inside electrical installations, control systems, battery systems, PV systems, auxiliary supplies and equipment-specific wiring. This calculator stays with transparent arithmetic and user-entered values. Where AS/NZS 3008 cable data, AS/NZS 3000 installation context, local authority requirements, DNSP conditions, product instructions or manufacturer data affect the job, those sources remain controlling for the project record.

The calculator does not reproduce protected standards tables and does not embed product limits. It records the result from the values entered by the user so the result can be reviewed with the project documents. For battery and PV work, use the specialist workflow when the DC run belongs to that system rather than treating this general page as a replacement.

Minimum export record

Stop points

• The review current is unknown or only guessed from a loose allowance.
• The one-way route length is still a drawing shortcut and the result is close to the entered target.
• Cable data is copied from a different conductor, temperature basis or installation assumption.
• The source value is complete-circuit mV/A/m but is being treated as single-conductor resistance, or the reverse.
• The calculated percentage is above the entered project target.
• Cable loss is material enough to raise heat or energy-loss questions.
• Equipment voltage tolerance, terminals, protection or product instructions are being treated as optional.
• The result is being used as final cable selection without checking current-carrying capacity, protection, terminations, installation conditions and manufacturer instructions.

The useful output is a repeatable calculation record, not just a percentage. Keep current, voltage, route length, cable data source and target together so another reviewer can repeat the result when the route or load changes.