Total voltage drop calculator
Add the drop of mains, submain and final against 5 %.
Reads AS/NZS 3008.1.2:2017 (NZ), AS/NZS 3008.1.1:2017 and 2025 (AU) and AS/NZS 3000:2018. Tables checked 1 Oct 2026.
Try a job 4
Each job fills in example values. Replace them with your values.
- Check the total voltage drop to a shedThe mains, the shed submain and a final subcircuit added against 5 %.
- Find the drop left for a new circuitWhat 25 m of mains and a 40 m submain leave for a final subcircuit.
- Add a three phase submain to a finalThree phase mains and submain with a single phase final, added by percent.
- Use the 7 % substation limitA factory fed from its own transformer, checked against 7 %.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Point of supply
- Network supply (5 % limit)
- Standard
- NZ · AS/NZS 3008.1.2
- Power factor
- 0.9
- Parts of the run, from the point of supply
- 3 rows
Total voltage drop
4.25%
- Voltage drop limit
- 5%
- Mains and submains
- 1.98%
- Left for a final subcircuit
- 3.02%
- Left at the point of use
- 0.75%
This result is a design aid. Verify it against the current standard.
Calculation steps
- Row 1Consumer mains
- Row 1 mV/A·m2.6mV/A·m
AS/NZS 3008.1.2:2017 Cl 4.5
- Row 1 voltage drop2.6V
- Row 1 voltage drop, percent of 230 V1.13%
AS/NZS 3000:2018 App C Para C4.1
- Running total after row 11.13%
AS/NZS 3000:2018 App C Para C4.1
- Row 2Submain
- Row 2 mV/A·m4.09mV/A·m
AS/NZS 3008.1.2:2017 Cl 4.5
- Row 2 voltage drop1.96V
- Row 2 voltage drop, percent of 230 V0.85%
AS/NZS 3000:2018 App C Para C4.1
- Running total after row 21.98%
AS/NZS 3000:2018 App C Para C4.1
- Row 3Final subcircuit
- Row 3 mV/A·m16.31mV/A·m
AS/NZS 3008.1.2:2017 Cl 4.5
- Row 3 voltage drop5.22V
- Row 3 voltage drop, percent of 230 V2.27%
AS/NZS 3000:2018 App C Para C4.1
- Running total after row 34.25%
AS/NZS 3000:2018 App C Para C4.1
- Voltage drop limit5%
AS/NZS 3000:2018 Cl 3.6.2
- Total voltage dropResult4.25%
AS/NZS 3000:2018 Cl 3.6.2
- Mains and submains1.98%
- Left for a final subcircuit3.02%
AS/NZS 3000:2018 Cl 3.6.2
- Left at the point of use0.75%
About this calculator
How this is calculated
AS/NZS 3000 limits the voltage drop from the point of supply to any point in the installation. It is one limit for the whole run, not one per circuit. So the drop in the consumer mains, every submain and the final subcircuit must add up to no more than the limit. This tool adds them.
You enter each part of the run in order from the point of supply: the consumer mains, up to three submains and the final subcircuit. For each part you give the phases, the current, the route length and the cable. The tool works each part with the same calculation as the voltage drop tool. It reads the cable's resistance and reactance from AS/NZS 3008.1, finds the mV/A·m at the power factor, and gives the drop in volts.
Each drop is then taken as a percent of that part's own circuit voltage: 230 V for single phase and 400 V for three phase. Appendix C of AS/NZS 3000 adds the percents directly, so a three-phase submain adds to a single-phase final subcircuit with no conversion. The running total is the drop at the end of each part.
The limit is 5 % of the nominal voltage. Where the point of supply is the low voltage terminals of a substation on the premises, which supplies only this installation, it is 7 %. The clause sets no split between the parts. The tool shows what the mains and submains take, and what that leaves for a final subcircuit from the last board.
| Step | Table or clause | What it decides |
|---|---|---|
| Resistance and reactance of each part | AS/NZS 3008.1 Tables 34 and 35 | The impedance of the cable |
| Drop of each part | AS/NZS 3008.1 Cl 4.5 | The mV/A·m and the drop in volts |
| Percent of each part | AS/NZS 3000 App C Para C4.1 | The drop as a percent of its circuit voltage, added part by part |
| The limit | AS/NZS 3000 Cl 3.6.2 | The most the total may be from the point of supply |
| A substation on the premises | AS/NZS 3000 Cl 3.6.2 Exception 3 | The higher limit where it applies |
| A load spread along a final subcircuit | AS/NZS 3000 Cl 3.6.2 Exception 1 | The current you may use for that part |
Worked examples
- A house: mains, a garage submain and a socket-outlet circuit. The total voltage drop is 4.25 %. The mains and submain take 1.98 %, which leaves 3.02 % for a final subcircuit.
- A shed 30 m from the house. The total voltage drop is 4.83 %, inside the 5 % limit but close to it. The upstream parts take 3.13 %, which leaves 1.87 % for a final subcircuit.
- A factory on its own substation. The total voltage drop is 6.27 % against the 7 % limit. The mains and submain take 4.38 %, which leaves 2.62 % for a final subcircuit.
- A farm workshop 60 m from the house. The total voltage drop is 10.82 %, so the run fails. The mains and submain take 8.55 % on their own, which leaves -3.55 % for a final subcircuit. A larger submain is the fix.
Limits
The tool works a.c. runs at 230 V and 400 V nominal. It does not check extra-low voltage circuits, which Cl 3.6.2 leaves out, or a stand-alone system, which Exception 4 judges on the utilisation voltage. Single-core parts use the highest reactance the table gives for the formation. Use the voltage drop tool for one run with a known formation or an unbalanced neutral.
Motor starting and other short transient drops are not part of the limit. Check those against the equipment.
See also: The 5 % voltage drop limit from supply to load, Total voltage drop: mains, submain and final and Voltage drop.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
Is the 5 % voltage drop for each circuit or the whole installation?
The whole installation. AS/NZS 3000 Cl 3.6.2 limits the drop from the point of supply to any point. The consumer mains, submains and the final subcircuit share one 5 %, so this tool adds them.
Is there a 2 % and 3 % split between mains and final subcircuits?
Not in AS/NZS 3000. Cl 3.6.2 sets one limit and no split. Designers often plan one, but the clause only asks that the total stays within the limit. The tool shows what the mains and submains take and what is left.
How do I add a three-phase submain to a single-phase final subcircuit?
By percent. Each part is worked as a percent of its own circuit voltage, 400 V for three phase and 230 V for single phase. Appendix C of AS/NZS 3000 adds those percents directly.
When is the limit 7 %?
When the point of supply is the low voltage terminals of a substation on the same premises that supplies only this installation. Choose Own substation and the tool uses 7 %.
What current should I use for each part?
The maximum demand of each part, its connected load, or its protective device rating, whichever you know. A final subcircuit with its load spread along it may use half the device rating.
Clauses and tables this tool reads
- AS/NZS 3000:2018 App C Para C4.1Adding voltage drop by percent
- AS/NZS 3000:2018 Cl 3.6.2Voltage drop limit
- AS/NZS 3000:2018 Cl 3.6.2Voltage drop limit from the point of supply, and how the parts of an installation add
- AS/NZS 3008.1.2:2017 Table 30, 34, 35Reactance at 50 Hz and a.c. resistance at 50 Hz
- AS/NZS 3008.1.1:2017 Table 30, 34, 35Reactance at 50 Hz and a.c. resistance at 50 Hz
- AS/NZS 3008.1.1:2025 Table 4.1(A), 4.1(B), 4.5(A), 4.5(B)Reactance at 50 Hz and a.c. resistance at 50 Hz
Every clause and table, with how each was verified
Tables last checked on 1 Oct 2026.
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