Why is there no verdict on my reading?

Because the figures a reading is judged against are in AS/NZS 3000 and AS/NZS 3017, which this page names and links and does not reproduce. The tool sets your reading beside its own arithmetic and lists what to check.

Which resistivity does it use?

Copper at the International Annealed Copper Standard: 1/58 Ω·mm²/m (0.017241) at 20 °C, with the 20 °C temperature coefficient 0.00393 per °C, both from NBS Handbook 100, Copper Wire Tables. They are not the rounded figures the voltage drop tools disclose for their own estimates.

Where does Ze come from?

From you: measure it, or enter a figure from a document and name who or what documented it. The tool never supplies a Ze, and with Ze blank it shows no Zs.

Why is the result sometimes one value and sometimes a band?

Stranding and the difference between nominal and actual cross-section change a real conductor's resistance, and no allowance for either is assumed. Enter your own, for example from the cable maker's data, to see a band. Left blank, the result is one value labelled resistance-only, nominal cross-section; actual stranded conductors differ.

My reading is lower than the arithmetic. What should I check?

Parallel paths first: bonding, metallic enclosures, conduit or another earth carrying part of the test current. A larger conductor or a shorter run than the one entered also reads low.

Test Worksheet

Continuity and Loop Impedance Expectation

When an inverter or battery AC circuit, or an array bonding reading, looks high: the R1+R2, R2 and Zs the conductors you enter give by arithmetic, beside your measured value, with the difference and the causes to check.

Sources listedReviewed September 2026Our methodology

Inputs

View result

Expected (arithmetic) vs measured. The expectation is conductor resistance worked from the material, size, length and temperature you enter; it is not a test result and states no figure from AS/NZS 3000 or AS/NZS 3017. The installation rules sit in AS/NZS 3000 and inspection and testing in AS/NZS 3017.

What you are checking

CheckAn inverter or battery AC circuit, or an array bonding or earth conductor on its own.

Conductor materialCopper only. Aluminium is not offered because no cited constant for it could be matched to a cable conductor.

Conductors

One-way lengthThe route length from one end to the other, as installed or recorded.

Conductor size

Conductor temperature at the testYour estimate of the conductor's temperature when you tested. The copper coefficient is applied from 20 °C.

Band (optional)

Allowance for stranding and actual cross-sectionYour own allowance, for example from the cable maker's data. None is assumed. Left blank, the expectation is a single value labelled resistance only.

Your readings (optional)

Measured resistance

Live result

Edit inputs

Still needed: what you are checking; the conductor material; the one-way length; the conductor's cross-section; the conductor temperature at the test.

Key takeaways

Expected (arithmetic) vs measured. The expectation is conductor resistance worked from the material, size, length and temperature you enter; it is not a test result and states no figure from AS/NZS 3000 or AS/NZS 3017.
Resistance is ρ(T) × L ÷ A with the International Annealed Copper Standard resistivity and temperature coefficient from NBS Handbook 100. Copper only: aluminium is not offered.
Length, cross-sections, test temperature, Ze and any band all start empty. With no band entered the expectation is one value labelled resistance-only at the nominal cross-section, because actual stranded conductors differ.
Zs is Ze plus R1+R2, shown only when you enter Ze and where it came from. Your measured value is set beside the expectation with the difference and the causes to check, never a verdict.

How it works

Expected (arithmetic) vs measured. The expectation is conductor resistance worked from the material, size, length and temperature you enter; it is not a test result and states no figure from AS/NZS 3000 or AS/NZS 3017. How an installation is verified, and the figures a reading is judged against, are in AS/NZS 3000 and AS/NZS 3017. This page names them and reproduces nothing from either.

Resistivity. Copper at the International Annealed Copper Standard: ρ20 = 1/58 Ω·mm²/m (0.017241) with the temperature coefficient α20 = 0.00393 per °C, both from NBS Handbook 100, Copper Wire Tables (pp. 2, 3 and 9). The voltage drop and cable sizing calculators use a rounded figure for their own estimates; this tool uses the cited one, so the two can differ slightly.
Temperature. ρ(T) = ρ20 × (1 + α20 × (T − 20)), the linear form in the same handbook, at the conductor temperature you enter. Temperatures are accepted between −100 and 200 °C, the interval the handbook says the linear relation is assumed over.
Resistance. R = ρ(T) × L ÷ A for each conductor, with L the one-way length. R1+R2 adds the active and protective earth conductors; R2 is the protective earth or bonding conductor on its own.
Band. Stranding and the difference between a cable's nominal and actual cross-section move the real resistance away from ρL/A. No allowance is assumed: enter your own, for example from the cable maker's data, and the expectation becomes a band. Left blank, it is a single value labelled “resistance-only, nominal cross-section; actual stranded conductors differ”.
Zs. Zs = Ze + (R1+R2), shown only when you enter Ze and say where it came from: measured on this installation, or documented by a person or document you name. No Ze is ever supplied.
Measured. Your reading is set beside the expectation with the difference, and the causes worth checking: a loose termination, a wrong conductor size, a longer run than recorded, or parallel paths that make a reading low.

Aluminium is not offered: the published aluminium figures are given per alloy and temper, and which applies to a given cable conductor could not be sourced. When a circuit keeps operating its protection, work through the repeated tripping playbook. For sizing rather than checking, the cable sizing calculator and the voltage drop calculator work from the same conductor inputs.

Arithmetic from the values you enter, for working out why a reading looks the way it does. It is not a test result, a record of verification or a certificate. The maths runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately save the result.

Source ledger3 sources

ResearchCopper Wire Tables, NBS Handbook 100 — National Bureau of Standards (now NIST)
Standards bodyAS/NZS 3000:2018 — Standards Australia catalogue
Standards bodyAS/NZS 3017:2022 — Standards Australia catalogue

Best next action

AS/NZS 3000Do this next AS/NZS 3017Standard Solar Circuit Repeatedly TrippingPlaybook

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Good to know

Frequently asked

Why is there no verdict on my reading?: Because the figures a reading is judged against are in AS/NZS 3000 and AS/NZS 3017, which this page names and links and does not reproduce. The tool sets your reading beside its own arithmetic and lists what to check.
Which resistivity does it use?: Copper at the International Annealed Copper Standard: 1/58 Ω·mm²/m (0.017241) at 20 °C, with the 20 °C temperature coefficient 0.00393 per °C, both from NBS Handbook 100, Copper Wire Tables. They are not the rounded figures the voltage drop tools disclose for their own estimates.
Where does Ze come from?: From you: measure it, or enter a figure from a document and name who or what documented it. The tool never supplies a Ze, and with Ze blank it shows no Zs.
Why is the result sometimes one value and sometimes a band?: Stranding and the difference between nominal and actual cross-section change a real conductor's resistance, and no allowance for either is assumed. Enter your own, for example from the cable maker's data, to see a band. Left blank, the result is one value labelled resistance-only, nominal cross-section; actual stranded conductors differ.
My reading is lower than the arithmetic. What should I check?: Parallel paths first: bonding, metallic enclosures, conduit or another earth carrying part of the test current. A larger conductor or a shorter run than the one entered also reads low.
Is my data stored or sent anywhere?: The calculation runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately select Save result.

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