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Site cord length calculator

The longest a cord or cable may run on a construction site.

AS/NZS 3012

Reads AS/NZS 3012:2019. Tables checked 1 Oct 2026.

Try a job 5

Each job fills in example values. Replace them with your values.

Inputs

Worked example with the default inputs. The live calculator replaces it when the page loads.

Rated current
10 A
Conductor area
2.5 mm²
Cable
Single phase, 3 core
Use
General use, such as saws, grinders and drills
Total length from the socket-outlet to the equipment
40 m
PSOA supply lead
0 m
Voltage drop the fixed wiring uses before the socket-outlet
0 %
Two or more cord extension sets are joined
No
The cord is used coiled or on a reel
No

Maximum length

60m

Length checked
40m
PSOA supply lead
0m
Inside the limit
Yes
Voltage drop the length is based on
5%
Voltage drop already used upstream
0%
Total voltage drop at the equipment
5%
Reference
AS/NZS 3012:2019 Table 1

This result is a design aid. Verify it against the current standard.

Calculation steps

  1. Length entered40m

    AS/NZS 3012:2019 Table 1

  2. PSOA supply lead0m

    AS/NZS 3012:2019 Cl 2.6.10(b)

  3. Length checked against Table 140m

    AS/NZS 3012:2019 Table 1

  4. Rated current10A

    AS/NZS 3012:2019 Table 1

  5. Conductor area2.5mm²

    AS/NZS 3012:2019 Table 1

  6. Voltage drop the length is based on5%

    AS/NZS 3012:2019 Table 1

  7. Voltage drop already used upstream0%

    AS/NZS 3012:2019 Table 1

  8. Total voltage drop this length implies5%

    AS/NZS 3012:2019 Table 1

  9. Maximum length60m

    AS/NZS 3012:2019 Table 1

  10. General use, single phaseResult60m

    AS/NZS 3012:2019 Table 1

  11. General use, three phase120m

    AS/NZS 3012:2019 Table 1

  12. Specific use, single phase35m

    AS/NZS 3012:2019 Table 1

  13. Specific use, three phase70m

    AS/NZS 3012:2019 Table 1

About this calculator

How this is calculated

The tool checks a cord or flexible cable on a construction site. It uses the length limit in AS/NZS 3012:2019 Table 1. The limit depends on the rated current, the conductor area, the use and the phases.

  1. Length entered. You enter the length of the cord run. You can add the length of the PSOA supply lead, under Cl 2.6.10(b).
  2. Length checked. The tool adds the two. It checks that total against Table 1.
  3. Rated current and area. It reads the Table 1 row for your rated current and conductor area.
  4. Use and phases. It picks the column: general or specific use, single or three phase.
  5. Maximum length. It gives the Table 1 length. The inside-the-limit answer passes when the length checked is at or under it.
  6. Total drop. The Table 1 length is based on a 5 % drop. The tool adds the drop already used upstream and gives the total at the equipment.
StepTable or clauseWhat it decides
PSOA leadAS/NZS 3012 Cl 2.6.10(b)The length counted with the cord
Maximum lengthTable 1The limit for the rating, area and use
Total dropTable 1The drop at the equipment, with the upstream drop

Worked example

A 10 A single-phase cord of 1.5 mm², 50 m long, for general use. The maximum length is 35 m. The 50 m run fails. A 2.5 mm² cord at 40 m passes, with a maximum of 60 m.

Limits

  • The 5 % drop is in addition to the drop the fixed installation already used. Enter the real upstream drop.
  • A zero upstream drop is the default. Treat it as optimistic.
  • The figures suit ordinary site power tools.
  • The smallest flexible cord conductor is 1 mm². Every cord carries its own earth conductor.
  • Cord extension sets use heavy duty sheathed cable (Cl 2.6.3).
  • Do not use double adaptors or piggyback plug adaptors (Cl 2.6.6).

See also: Construction site supplies, AS/NZS 3012, Builder's pole house build supply, RCDs and cord lengths and the site supply tool.

Questions

Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.

How long can an extension cord run on a construction site?

Table 1 of AS/NZS 3012:2019 gives a limit for each rated current and conductor size. A 10 A, 2.5 mm² single phase cord for general use stops at 60 m. The three phase, four core cable of that size reaches 120 m.

What is the difference between general use and specific use?

General use covers everyday site tools such as saws, grinders and drills. Its lengths allow a 5 percent drop at the rated current. Specific use is for equipment where a failed motor start puts someone at risk. Its lengths allow 3 percent, so they are shorter.

Does the table's voltage drop include the fixed wiring?

No. The table's percentage adds to the drop the fixed wiring already uses before the socket-outlet. Enter that figure, and the tool shows the total at the equipment. Every result says so.

Can I join two extension leads together?

Yes, if the whole run stays inside one Table 1 limit. Enter the total of every joined set, and the tool checks that sum. A PSOA supply lead counts too, so the tool adds it. AS/NZS 3012 recommends a single set, and says not to use a cord coiled or on a reel.

What is the smallest cord conductor allowed?

Cl 2.6.2 sets 1.0 mm² as the floor for each core of a flexible cord. The cord also needs an earth conductor beside its live conductors.

Clauses and tables this tool reads

Every clause and table, with how each was verified

Tables last checked on 1 Oct 2026.

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