Should I use the R, X, or Z column from the voltage drop tables?

For general-purpose power circuits at or near unity power factor, use the combined Z column — this gives the conservative worst-case value. For circuits with known low power factors (such as motor circuits or heavily inductive loads), you can calculate a more precise voltage drop using VD = I × L × (r×cosφ + x×sinφ) / 1000, where r and x are the separate resistive and reactive columns. For small cables below 16mm², the reactive component is negligible and R alone is sufficient.

Does AS/NZS 3000 have different voltage drop limits for lighting versus power?

No. Unlike BS 7671 which specifies 3% for lighting and 5% for other uses, AS/NZS 3000:2018 applies a single 5% limit to all circuit types including lighting. However, good design practice often limits lighting circuits to 2-3% to avoid visible flicker and dimming, even though the standard does not mandate it.

How does the voltage drop change if I use aluminium cable instead of copper?

Aluminium has approximately 1.6 times the resistivity of copper, so for the same cross-sectional area, the mV/A/m value is roughly 60% higher. For example, a 16mm² copper cable might have 2.76 mV/A/m (Table 35) while a 16mm² aluminium cable has 4.53 mV/A/m (Table 37). To achieve similar voltage drop performance with aluminium, you typically need to go up one or two cable sizes (e.g., 25mm² aluminium instead of 16mm² copper).

Voltage Drop Calculator — AS/NZS 3008.1.1 🇦🇺

Australia & New ZealandEdition 2017 / AS/NZS 3000:2018 (Amendment 2:2025)Free Online Tool

Voltage drop in Australian and New Zealand electrical installations is governed by AS/NZS 3008.1.1:2017 (Selection of Cables) and AS/NZS 3000:2018 (Wiring Rules). The Wiring Rules impose strict limits on voltage drop to ensure equipment operates within its rated voltage tolerance and to minimise energy losses across conductor runs.

AS/NZS 3008.1.1 provides pre-calculated mV/A/m values in Tables 35 through 40, covering single-phase and three-phase circuits for both copper and aluminium conductors across all common insulation types. These tabulated values already incorporate conductor resistance and reactance at the rated conductor operating temperature, simplifying the calculation to a single multiplication. The standard covers thermoplastic (V-75, V-90) and thermosetting (X-90, X-HF-110) insulation types, each with distinct mV/A/m values reflecting their different maximum operating temperatures.

Under AS/NZS 3000 Clause 3.6.2, the total voltage drop from the point of supply to any point of utilisation must not exceed 5% of the nominal supply voltage. This 5% budget must be shared between consumer mains, sub-mains, and final sub-circuits, making careful allocation essential during design.

Open Voltage Drop Calculator

How Voltage Drop Works Under AS/NZS 3008.1.1

Voltage Drop Methodology per AS/NZS 3008.1.1:2017

The voltage drop calculation under AS/NZS 3008.1.1 uses a tabulated approach. Rather than calculating resistance and reactance separately, the standard provides composite mV/A/m (millivolts per ampere per metre) values that account for both the resistive and reactive voltage drop components at the conductor's maximum operating temperature.

Step 1: Determine Circuit Parameters

Identify the design current I_b (in amperes), the route length L (in metres, one-way distance from the distribution board to the load), the supply voltage V_s (230V single-phase or 400V three-phase per AS 60038), and whether the circuit is single-phase or three-phase.

Step 2: Look Up the Tabulated mV/A/m Value

Select the appropriate table based on circuit configuration and conductor material:

Table 35 — Single-phase copper conductors (mV/A/m)
Table 36 — Three-phase copper conductors (mV/A/m)
Table 37 — Single-phase aluminium conductors (mV/A/m)
Table 38 — Three-phase aluminium conductors (mV/A/m)

Within each table, locate the row for the conductor cross-sectional area (mm²) and the column for the insulation type. The tables give separate columns for resistive (r) and reactive (x) components, plus a combined (z) value at different power factors. For most general loads at unity or near-unity power factor, the combined column is used directly.

Step 3: Calculate Voltage Drop

Apply the formula per AS/NZS 3008.1.1 Clause 4.5:

VD (volts) = (mV/A/m × I_b × L) / 1000

Where mV/A/m is the tabulated value, I_b is the design current, and L is the one-way route length. The factor of 1000 converts millivolts to volts. Note that for single-phase tables, the mV/A/m value already accounts for the go-and-return conductor path (factor of 2 is embedded).

Step 4: Calculate Percentage Voltage Drop

VD% = (VD / V_supply) × 100

For a 230V single-phase circuit, divide by 230. For a 400V three-phase circuit, divide by 400.

Step 5: Check Compliance with AS/NZS 3000 Clause 3.6.2

The total voltage drop from the point of supply to the most distant point of utilisation must not exceed 5% of the nominal voltage. This means 11.5V for a 230V supply or 20V for a 400V supply. The 5% budget is cumulative: if consumer mains use 2%, only 3% remains for the combined sub-mains and final sub-circuits. Table 39 in AS/NZS 3008.1.1 provides recommended voltage drop allocations for different installation segments.

Step 6: Consider Conductor Operating Temperature

The tabulated mV/A/m values are given at the conductor's maximum operating temperature (e.g., 75°C for V-75 insulation). When the actual conductor load is less than the cable's current rating, the real operating temperature is lower, which reduces resistance and actual voltage drop. Clause 4.5.2 provides a correction method for conductors operating below their rated temperature, though in practice many engineers use the conservative tabulated values.

Key Reference Tables

Table 35 — Voltage Drop, Single-Phase, Copper Conductors

Millivolts per ampere per metre (mV/A/m) for single-phase circuits with copper conductors. Lists values for V-75, V-90, X-90, and X-HF-110 insulation types across conductor sizes from 1mm² to 630mm².

Use for single-phase copper circuits. Select the row matching your cable size and the column matching your insulation type. The value already includes the go-and-return path.

Table 36 — Voltage Drop, Three-Phase, Copper Conductors

Millivolts per ampere per metre (mV/A/m) for three-phase balanced circuits with copper conductors. Values incorporate the √3 factor for three-phase systems across all standard insulation types.

Use for three-phase balanced copper circuits. For unbalanced three-phase loads, calculate the neutral current and assess the worst-case single-phase voltage drop separately.

Table 39 — Recommended Voltage Drop Allocation

Provides guidance on allocating the total 5% voltage drop budget across consumer mains, sub-mains, and final sub-circuits for different installation types (domestic, commercial, industrial).

Use during design phase to partition the voltage drop budget. Typical domestic allocation: 1.5% consumer mains, 1.5% sub-mains, 2% final sub-circuits.

AS/NZS 3000 Clause 3.6.2 — Maximum Voltage Drop

Mandates that voltage drop from the point of supply to any point of utilisation shall not exceed 5% of the nominal voltage. Applies to the cumulative drop across all circuit segments.

The compliance check for all voltage drop calculations. Sum the voltage drop across consumer mains, sub-mains, and final sub-circuits and verify the total does not exceed 5% (11.5V at 230V, 20V at 400V).

Table 37 — Voltage Drop, Single-Phase, Aluminium Conductors

Millivolts per ampere per metre (mV/A/m) for single-phase circuits with aluminium conductors. Aluminium values are higher than copper due to its higher resistivity (approximately 1.6× copper).

Use for single-phase aluminium circuits, commonly found in consumer mains and larger sub-mains. Aluminium cables start at 16mm² minimum in these tables.

Table 40 — Voltage Drop, Multicore Cables

Provides mV/A/m values for multicore cables (3-core and 4-core) in both copper and aluminium, accounting for the different thermal characteristics of bundled conductors.

Use when installing multicore cables rather than single-core cables in trefoil or flat formation. Values differ slightly from single-core tables due to mutual heating effects.

Worked Example — AS/NZS 3008.1.1 Voltage Drop

Scenario

A single-phase 230V circuit supplies a 20A load via 4mm² copper cable with V-75 (PVC) insulation, installed in conduit. The cable route length is 30 metres from the distribution board to the final outlet.

Identify circuit parameters

Design current I_b = 20A, route length L = 30m, supply voltage = 230V single-phase, cable = 4mm² Cu, insulation = V-75.

Look up mV/A/m from AS/NZS 3008.1.1 Table 35

For 4mm² copper conductor with V-75 insulation, single-phase: the tabulated value is 11.0 mV/A/m (resistive component r = 10.9, reactive component x = 0.170, combined z = 11.0 at unity power factor).

mV/A/m = 11.0 (from Table 35, 4mm² row, V-75 column)

11.0 mV/A/m

Calculate voltage drop in volts

Apply the standard voltage drop formula from Clause 4.5.

VD = (mV/A/m × I_b × L) / 1000 = (11.0 × 20 × 30) / 1000

VD = 6.60V

Calculate percentage voltage drop

Express the voltage drop as a percentage of the 230V nominal supply voltage.

VD% = (6.60 / 230) × 100

VD% = 2.87%

Check compliance with AS/NZS 3000 Clause 3.6.2

The maximum allowable total voltage drop is 5% (11.5V). This final sub-circuit contributes 2.87%. If the upstream consumer mains and sub-mains contribute up to 2.13%, the total remains within the 5% limit. A typical allocation per Table 39 allows about 2% for a final sub-circuit, so 2.87% may require review of the upstream VD budget or an increase to 6mm² cable.

2.87% < 5% total limit — PASS for this segment (but verify cumulative VD)

The 4mm² cable produces a voltage drop of 6.60V (2.87%) over the 30m run. While this is within the overall 5% limit, it consumes a significant portion of the budget. If the consumer mains and sub-mains already use 2% or more, consider upgrading to 6mm² (mV/A/m = 7.3) which would reduce the drop to 4.38V (1.90%), leaving more headroom for the upstream segments.

Common Mistakes When Using AS/NZS 3008.1.1

1
Confusing single-phase and three-phase mV/A/m values — Table 35 values already include the factor-of-2 for go-and-return, while Table 36 values include the √3 factor. Using single-phase values for a three-phase calculation (or vice versa) gives significantly wrong results.
2
Not considering the cumulative voltage drop across all circuit segments — AS/NZS 3000 Clause 3.6.2 applies to the total drop from point of supply to point of utilisation, not just the final sub-circuit. A cable that passes individually may cause the total installation to fail.
3
Using the wrong insulation column for conductor temperature — V-75 operates at 75°C and V-90 at 90°C, with different resistance values. Selecting V-75 values for a V-90 cable underestimates the voltage drop because V-90 has higher operating temperature and therefore higher resistance.
4
Forgetting to account for reactive component on large cables — For cables 25mm² and above, the reactive voltage drop (X component) becomes significant. Using only the resistive (R) column instead of the combined (Z) column underestimates the total voltage drop, particularly at low power factors.
5
Applying voltage drop correction for operating temperature inconsistently — The tabulated values assume the conductor is at its maximum rated temperature. If the cable operates at a lower temperature (because load current is well below the cable rating), the actual voltage drop will be less, but this correction per Clause 4.5.2 must be applied correctly or not at all.

How Does AS/NZS 3008.1.1 Compare?

AS/NZS 3008.1.1 uses a tabulated mV/A/m approach that simplifies calculations by pre-computing the combined resistive and reactive components at rated conductor temperature. Unlike the IEC 60364 general formula method (which requires separate R and X values with power factor), the Australian tables let engineers read a single value and multiply. The 5% total voltage drop limit in AS/NZS 3000 is comparable to BS 7671's 5% for power circuits, but AS/NZS does not distinguish between lighting and power circuits — the same 5% applies to all.

Frequently Asked Questions

AS/NZS 3000:2018 Clause 3.6.2 limits the total voltage drop from the point of supply to any point of utilisation to 5% of the nominal voltage. For a 230V single-phase supply, this is 11.5V; for a 400V three-phase supply, this is 20V. This limit is cumulative across consumer mains, sub-mains, and final sub-circuits.

AS/NZS 3008.1.1 Table 39 provides recommended allocations. A common approach for domestic installations is 1.5% for consumer mains, 1.5% for sub-mains, and 2% for final sub-circuits. For industrial installations with long cable runs, you might allocate 1% to the main switchboard feeder and spread the remaining 4% across sub-distribution and final circuits. The allocation depends on the specific installation layout.

Yes. The single-phase tables (Tables 35 and 37) include the factor of 2 for the go-and-return path. You do not need to double the route length or the result. Similarly, the three-phase tables (Tables 36 and 38) incorporate the √3 factor. Simply multiply the tabulated value by the design current and the one-way route length.

Voltage Drop Calculator for Other Standards

🇬🇧BS 7671

🌍IEC 60364-5-52

🇺🇸NEC/NFPA 70