How to size cable in Australia
A practical guide for moving from load current to a traceable Australian cable-size candidate without replacing current standards or project review.
What cable sizing means here
In this site, cable sizing means checking whether a user-entered metric cable-size candidate is worth carrying forward. It is not a complete selection service. The workflow is useful when a project already has a load, a route, a candidate label and source data for current-carrying capacity or voltage drop.
The useful outcome is a clear record: current basis, candidate label, entered current-carrying-capacity source, voltage-drop data, route length, target and review result. That record can then move into current standards, project documentation, protection and installation review.
Review sequence
- Confirm the load current. Use known current where available, or calculate current from kW or kVA with the correct phase and voltage basis.
- Name the cable run. Keep board, circuit, equipment and drawing references visible.
- Enter the candidate metric cable-size label exactly as it appears in the project record.
- Enter current-carrying capacity from the project source, manufacturer data, reviewed design document or standards source document.
- Enter voltage-drop data that belongs to the same candidate and circuit context.
- Enter route length as the installed one-way path.
- Compare current-carrying capacity margin and voltage-drop margin together.
- Carry forward only with the source documents attached.
Candidate review matrix
| Review area | What to check | Why it changes the answer |
|---|---|---|
| Load basis | Current, kW, kVA, voltage, phase and power factor | A different current changes capacity and voltage-drop margins |
| Candidate label | Metric size, material and cable family | The label alone does not define current-carrying capacity |
| Current-carrying capacity | Source value in A and the basis behind it | Installation and derating assumptions can change the value |
| Voltage-drop data | mV/A/m or R/X values for the candidate | A mismatched data source changes the voltage-drop result |
| Route length | Installed one-way path | Long routes can fail voltage drop even when current margin exists |
| Protection context | Protective device, fault duty and withstand review | A cable can pass load checks and still need protection review |
Reading candidate outcomes
A carry-forward result means both entered comparisons have margin in the worksheet. It does not mean the cable is approved for installation. It means the candidate has enough arithmetic support to continue into project review with the source data attached.
A current-carrying capacity review result points to the current source, capacity source, installation basis or candidate label. A voltage-drop review result points to route length, data source, target, voltage basis or candidate label. If both checks need review, the candidate should not progress until both source chains are corrected.
Records that prevent rework
| Field | Record it as | Avoid |
|---|---|---|
| Candidate size | Metric label plus material where known | Label with no source |
| Current-carrying capacity | Value, source and installation basis | Bare amp value |
| Voltage-drop data | mV/A/m or R/X value and source | Data copied from another cable |
| Route | One-way installed path | Drawing shortcut |
| Target | Project review value and source | Habit-based percentage |
| Reviewer note | Limiting comparison and next check | Unqualified pass wording |
Boundaries
- Do not infer current-carrying capacity from the metric label alone.
- Do not publish or copy controlled cable-selection table values into the worksheet.
- Do not skip derating, grouping, installation method, protection, fault withstand or project documentation.
- Do not rely on a candidate review if source data cannot be traced.
- Do not treat a calculator result as an installation approval.