Voltage drop in Australian cable calculations
A workflow guide for checking Australian cable voltage drop with project current, route length, voltage basis and cable data.
When this guide fits
Use this guide when the question is not just the arithmetic result, but whether the voltage-drop inputs are ready to be entered. It suits final subcircuits, submains, equipment feeds, long lighting circuits and inverter AC cable records where the reviewer needs the current, route length, voltage basis and cable data to stay traceable.
The calculator gives volts, percent and receiving-end voltage. The guide keeps the surrounding record disciplined: why the current was used, how the route length was measured, where the cable data came from and what target was entered for the review.
Input sequence
- Identify the circuit, board, equipment feed or cable run being checked.
- Confirm whether the calculation uses single-phase or three-phase supply.
- Enter the voltage basis that belongs to the record.
- Use a reviewed current where possible, or keep the kW or kVA conversion basis with the record.
- Measure or estimate the installed one-way route length, including risers and route deviations.
- Enter mV/A/m or R/X data from a source that matches the selected cable context.
- Enter the project voltage-drop target and keep the source of that target with the record.
Input review table
| Input | Strong source | Weak source | Stop point |
|---|---|---|---|
| Voltage basis | Project documents, equipment data or measured value | Unchecked nominal assumption | The value does not match the circuit arrangement |
| Load current | Design current, nameplate current or measured current | Rough allowance | A reviewed current exists elsewhere |
| Route length | Installed one-way cable path | Straight drawing distance | Known risers or deviations are missing |
| Cable data | Project, manufacturer or standards source matching the run | Value copied from a different cable context | Material, arrangement or source cannot be identified |
| Project target | Project note, authority context or design requirement | Habit or old template | Target is being treated as a final rule without source |
Reading the result
Read voltage drop in volts and percent together. The percent is only meaningful when the voltage basis is visible. A result of 3 V means something different on a 230 V final circuit than on a 400 V three-phase run, and neither number is complete without current, length and cable data.
When the result is above the entered target, name the limiting assumption before changing the cable. The issue may be the route, the load basis, the project target, the data source or the candidate cable. The calculator result should lead to a review note, not an automatic design decision.
Record to keep
| Record field | Why it matters | Example note |
|---|---|---|
| Circuit reference | Ties the calculation to a real run | DB-1 final circuit 4 |
| Voltage and phase | Makes the percent repeatable | 230 V single phase |
| Current source | Explains why the current was used | 32 A design current |
| Route length | Shows the cable path basis | 42 m one-way route |
| Cable data source | Connects the formula to the selected context | Project mV/A/m value |
| Target source | Separates review target from final decision | Project 5 percent target |
| Result summary | Gives the next reviewer the arithmetic result | 4.7 V, 2.04 percent |
Boundaries
- Do not use voltage drop alone to select a cable.
- Do not use a cable data value when the conductor, material, installation basis or source is unknown.
- Do not treat a percentage result as complete without the voltage basis, current, route length and data source.
- Do not replace DNSP, local authority, product or project requirements with calculator output.
- Do not copy protected cable table values into a public worksheet.