Voltage drop vs current-carrying capacity
How to keep voltage-drop checks and current-carrying capacity checks separate when reviewing Australian cable candidates.
Two different checks
Voltage drop and current-carrying capacity answer different questions. Voltage drop asks how much voltage is lost along the run. Current-carrying capacity asks whether the candidate can carry the load current under the reviewed installation conditions.
Both checks can use the same project current and cable label, but they are not the same decision.
Comparison workflow
- Calculate or confirm the load current.
- Record the cable candidate and route length.
- Run the voltage-drop calculator using the correct voltage basis and conductor data.
- Run the cable-size candidate comparison using the entered current-carrying capacity source.
- Review the limiting check before carrying the candidate forward.
Difference table
| Check | Main inputs | Output | Common limiting condition |
|---|---|---|---|
| Voltage drop | Current, length, voltage, phase and conductor data | Drop in V and percent | Long route or high impedance |
| Current-carrying capacity | Load current and reviewed capacity value | Margin between load and capacity | Installation method, grouping or ambient conditions |
| Candidate review | Both sets of values | Carry-forward or review state | Either check can control |
Reading combined results
If only voltage drop needs review, look first at route length, voltage basis, conductor data and target. If only current-carrying capacity needs review, look first at the source value, derating assumptions and cable candidate.
If both checks need review, avoid patching only the easier number. The candidate may need a different size, material, route, installation basis or project assumption.
Boundaries
- Do not use voltage drop as a substitute for current-carrying capacity.
- Do not use current-carrying capacity as a substitute for voltage-drop review.
- Do not hide the source of either value.
- Do not treat a dual-margin result as full installation approval.