Voltage drop in Australian cable runs
How voltage drop is read in Australian 230/400 V cable work, including route length, conductor data and percent-drop checks.
What Voltage Drop Means
Voltage drop is the reduction in voltage along a cable run caused by current flowing through conductor impedance. In Australian low-voltage work it is usually read against the voltage basis for the run: 230 V a.c. active-to-neutral for many single-phase final circuits, or 400 V a.c. line-to-line for many balanced three-phase runs.
The result is normally shown as volts and percent. The percent is not meaningful unless the reference voltage is visible, because a 6 V drop is a different percentage on a 230 V run than on a 400 V run.
Inputs That Decide The Result
Voltage-drop review needs more than a cable size label. It needs the load current, route length, voltage basis, phase arrangement and conductor data used for that specific run. The same load can produce a different result when the route is longer, the conductor material changes, or the calculation moves from a final subcircuit to a submain.
Two common relationship styles appear in AUWiring tools and charts:
- With entered mV/A/m data:
voltage drop V = mV/A/m x current A x route length m / 1000. - With entered conductor impedance: single-phase uses a two-conductor factor; balanced three-phase uses
sqrt(3)with the line current and line-to-line voltage basis. - Percent drop is
voltage drop V / nominal voltage V x 100.
| Input | Typical Australian basis | Why it matters |
|---|---|---|
| Voltage basis | 230 V single-phase, 400 V three-phase or project-entered value. | Percent drop depends on the reference voltage. |
| Current basis | Known current, or current calculated from kW/kVA, phase and power factor. | Voltage drop rises with current. |
| Route length | Installed one-way route length in metres, entered consistently. | Longer routes increase the drop. |
| Conductor data | mV/A/m or resistance/reactance data for the actual cable. | Copper, aluminium, insulation and construction data are not interchangeable. |
| Target percent | Project review value entered by the user. | The calculator compares the result with the entered target, not a hidden universal rule. |
Worked Cable-Run Example
For a 230 V single-phase final subcircuit carrying 18 A over a 24 m route, entered cable data of 5.6 mV/A/m gives:
5.6 x 18 x 24 / 1000 = 2.42 V.
The percent drop is 2.42 / 230 x 100 = 1.05%. That is a voltage-drop result for that run only. It does not say the cable is acceptable for current-carrying capacity, protection or installation conditions.
| Run detail | Example entry | Review note |
|---|---|---|
| Supply context | 230 V final subcircuit, 50 Hz Australian low-voltage context. | Use the actual project voltage if it differs. |
| Load current | 18 A from the load schedule or circuit design note. | A different current changes the result. |
| Route length | 24 m one-way route length. | Keep length basis consistent across worksheets. |
| Cable data | 5.6 mV/A/m from the selected cable data source. | Do not borrow data from another material or cable family. |
Separate It From Current-Carrying Capacity
A cable can pass voltage drop and fail current-carrying capacity, or pass current-carrying capacity and fail voltage drop. Voltage drop is sensitive to route length and conductor impedance. Current-carrying capacity is sensitive to installation method, grouping, ambient temperature, enclosure, product data and derating source.
Keep both checks visible for final circuits, consumer mains, submains, distribution-board feeders and inverter AC runs. A candidate cable should not move forward just because one of the two checks looks comfortable.
Next checks
- Use the voltage-drop calculator when the current, route length, voltage basis and cable data are known.
- Use the voltage-drop formula chart when the relationship between mV/A/m, impedance, volts and percent needs to be checked.
- Use the cable-size workflow after voltage-drop review so current-carrying capacity, derating and protection remain separate.
Boundaries
- This page does not select a cable size or protective device.
- It does not reproduce AS/NZS 3008 cable tables or provide universal voltage-drop allowances.
- Project documents, current standards context, DNSP conditions where relevant, manufacturer data, installation conditions and competent review can override a general worked example.
Voltage drop in Australian cable runs in Australian work
Explain voltage drop in Australian cable runs so users can keep voltage basis, route length, current and conductor data together. The useful record is not just the final number or definition; it is the combination of the entered value, the supply arrangement, the equipment or circuit reference and the decision that still needs project review.
Help users understand voltage drop in Australian 230/400 V cable runs before checking a final circuit, submain, consumer mains or inverter AC run. Keep the wording in Australian English, use metric units, and treat 230/400 V a.c. at 50 Hz as the ordinary low-voltage context unless the project information states a different value.
Checks that belong beside this page
- Regional scopeAustralia; public cable calculation terminology.
- Standards contextAS/NZS 3008 context and Australian 230/400 V a.c. supply context; current project and licensed data remain controlling sources.
- Review timingReview cadence: Annual voltage-drop wording review or sooner if cable calculator, chart or guide wording changes.. Update trigger: Update when voltage-drop calculator inputs, formula chart rows or cable guide boundaries change.
Practical use sequence
For Voltage drop in Australian cable runs, begin with the circuit, board, load, cable route, equipment item or measurement record named by this topic. Record the value basis, such as current, voltage, kW, kVA, route length, test value, product rating, tariff value or worksheet field, then note the review boundary so another person can see what this page explained and what still needs a project decision.
The strongest Voltage drop in Australian cable runs record is specific enough to be reviewed later. It names the Australian context, keeps the entered assumptions visible, separates calculation support from compliance decisions and shows where a calculator, table, chart or term definition should be opened next.
Record detail to capture
Keep the Voltage drop in Australian cable runs note attached to Australia; public cable calculation terminology.. When the page is used during design, estimating, testing, review or study work, write the entered assumption, the source that supplied it, the circuit or equipment label and the person or role that must review the following action.
For Voltage drop in Australian cable runs, the review cadence is Annual voltage-drop wording review or sooner if cable calculator, chart or guide wording changes. and the update trigger is Update when voltage-drop calculator inputs, formula chart rows or cable guide boundaries change.. If the topic connects to Australian supply voltage, open that page after the current definition, input basis or boundary has been recorded, so the next calculation inherits the right Australian context.
A complete Voltage drop in Australian cable runs record leaves four facts visible: why the page was opened, which Australian supply or equipment context applies, which value remains user-entered and what later change would alter the result. That makes the page useful as a working note instead of a loose reference copied away from the project evidence.
- InputsWrite down the entered values and their units before comparing results across calculators or reference pages.
- LocationKeep the value tied to the board, circuit, cable run, equipment terminal, supply point or worksheet row it describes.
- Authority checkCompare the record with current Australian requirements, DNSP or local authority conditions and product information.
- Review trailRetain the date, edition context and reason for the calculation so later changes can be traced.
Connected AUWiring pages
Use the related pages for Voltage drop in Australian cable runs when the topic needs a calculator input, lookup table, formula chart or supporting term before the project record is complete. Open Australian supply voltage first when that page owns the next value or definition.
- Australian supply voltageVoltage basis for Australian 230/400 V cable checks.
- Metric cable sizesMetric conductor labels used in cable worksheets.
- Voltage-drop formulasFormula relationships used by voltage-drop calculators.
- Voltage dropUse entered current, length, voltage and conductor data for project-specific review.