Cable Sizing Chart Australia: What Size Cable Do I Need?

By ARCK Electrical · Trade counter, North Parramatta · Reviewed May 2026

Quick Q&A — click to expand

What size cable for a 32A oven? +

6mm² Twin & Earth is the default for a 32A electric oven circuit on a residential install. 4mm² will sometimes carry a smaller (~25A) oven if the run is short and the install method supports it, but most sparkies default to 6mm² to keep voltage-drop and derating headroom comfortable. Always confirm against AS/NZS 3008 for the actual install conditions.

Can I use 1.5mm for power points? +

No — general-purpose outlet circuits in Australia are run in 2.5mm² minimum. 1.5mm² doesn't have the current rating for a typical 16–20A GPO circuit, and using it would fail inspection. 1.5mm² is fine for lighting circuits on a 10A MCB and for some dedicated single-appliance circuits, but not for GPOs.

How do I work out voltage drop? +

Use Vd = (length × current × mV/A/m) / 1000, with mV/A/m from AS/NZS 3008.1.1 Table 41. AS/NZS 3000 caps total drop at 5% from supply to load — most sparkies work to 3% on the final sub-circuit and 2% on mains and sub-mains. Anything over about 25m on a final sub-circuit deserves a quick check.

What's the difference between TPS and circular cable? +

TPS (Twin & Earth) is the flat fixed-building wire you run in walls, ceilings, and conduits indoors. Orange circular is a round, tougher-sheathed cable built for outdoor, buried, or surface-exposed runs. They're sized off the same current tables but constructed to different parts of AS/NZS 5000.

What size sub-main for an 80A board? +

25mm² Cu is the typical pick for an 80A single-phase sub-main on a residential install — assuming a reasonable route length and standard install method. Longer runs can push you to 35mm² to keep voltage drop in check. Three-phase 80A boards are often sized differently again. Run the numbers for the specific job.

Picking the wrong cable size is the kind of mistake that doesn't show up the day you wire it.

It shows up six months later when the run gets warm under load, an RCBO keeps tripping, or a final inspection sends you back out to pull a sub-main you should have sized up in the first place.

This guide is the cable sizing reference we hand out at the counter when sparkies ask what size to drop in.

It covers the three things that actually determine cable size in Australia — current, voltage drop, and installation method — and gives you a clear chart of what suits the jobs you'll run into on a typical residential or light commercial fit-out.

A note before we start: cable sizing is regulated by AS/NZS 3008.1.1 (cable selection) and the cable itself is built to AS/NZS 5000. The numbers below are typical for common residential installation methods.

For anything outside the ordinary — long runs, bundled circuits, buried cable, high ambient temperatures — go to the standard and run the numbers properly.

Why cable size actually matters

Three things go wrong when a cable is undersized:

1. The cable runs hot. Current heats the conductor. The bigger the conductor, the less it heats up. When a cable is undersized for its load, the insulation runs near its temperature limit, ages early, and eventually fails. A V90 cable rated to 90°C at the conductor doesn't run forever at 90°C — it shortens its life.

2. Voltage drop bites you at the load. Every metre of cable drops a little voltage. The smaller the cable, the more drop per metre. Drop too much and your downlights look dim, your motor stalls under load, or your electronics misbehave. AS/NZS 3000 puts a hard cap on this — more on that below.

3. Protection won't see a fault. If the cable impedance is too high, a short-circuit fault at the far end might not draw enough current to trip the breaker in time. Sizing isn't just about steady-state load — it's about fault current too.

The three things that decide cable size

Cable selection is a balance between three numbers.

Current-carrying capacity (Iz). The cable has to carry the design current of the circuit indefinitely without overheating. Iz depends on the cable's construction, the installation method, ambient temperature, and whether it's grouped with other cables. AS/NZS 3008 gives the tables.

Voltage drop (Vd). AS/NZS 3000 limits voltage drop to 5% from the point of supply to the point of use. Most sparkies work to a 3% target on the final sub-circuit and leave 2% for consumer mains and sub-mains. Long runs, low-voltage loads, and lighting circuits will often be sized up to keep Vd in check, not because the current rating needs it.

Installation method. A cable clipped to a surface in free air carries more current than the same cable buried in thermal insulation or bundled with five others in a conduit. The same 2.5mm² T&E will be rated very differently depending on which of those it is. AS/NZS 3008 lists the methods (A1, B1, C, D, etc.) and gives a current rating for each.

Always pick the cable that satisfies all three. Whichever requirement is hardest to meet decides the size.

Cable sizing chart for typical residential use

This is the chart we use as a starting point at the counter.

It assumes single-phase 2-core+earth V90 PVC cable (the Twin & Earth most of you use), installed enclosed in a wall, partial thermal insulation, ambient 40°C — i.e. the conditions on a typical Sydney house. For anything outside that, go to AS/NZS 3008.

Cable size	Typical residential current capacity	Typical uses
1.0mm²	up to ~13A	Small lighting circuits. Many sparkies skip 1mm and run 1.5mm for headroom.
1.5mm²	up to ~16A	Lighting circuits, 10A dedicated single-appliance circuits, short ceiling fan drops.
2.5mm²	up to ~20A	General-purpose 16–20A GPO circuits, kitchen circuits, smaller hot-water units.
4.0mm²	up to ~25A	Hot water systems, smaller electric ovens, longer GPO runs, split-system AC.
6.0mm²	up to ~32A	Larger electric ovens, ducted AC, small sub-mains, EV chargers up to 32A.
10mm²	up to ~50A	Sub-mains to garages and granny flats, larger ducted systems, 40–50A loads.
16mm²	up to ~63A	Sub-mains for larger jobs, smaller consumer mains, three-phase 32A feeders.
25mm²	up to ~80A	Consumer mains for a typical 80–100A single-phase home.

A few notes on this table:

• These are guideline numbers. The same 2.5mm² T&E run in a hot roof space, bundled with three other circuits and surrounded by insulation, will sit well below 20A capacity.
• Aluminium consumer mains are common for the run from the meter to the board — that's a separate sizing exercise (and we stock both copper and aluminium).
• For three-phase, the per-conductor current is what matters and ratings are usually slightly higher per mm² because each phase shares the load.

Real-world residential examples

A handful of common Sydney jobs and the cable we'd usually drop in:

Lighting circuit, 10A MCB, ~80m total run. 1.5mm² T&E will carry the current easily, but on an 80m run the voltage drop sets the size. At ~29 mV/A/m, 1.5mm × 10A × 80m gives well over 5% drop. Move to 2.5mm² (≈18 mV/A/m) and the drop comes back under 3%.

General-purpose GPO circuit, 20A RCBO. 2.5mm² T&E. Standard. The only thing that changes the answer is a long run or heavy insulation around the cable.

Wall-mounted electric oven, 32A MCB. 6mm² T&E is the default. If the run is short and AS/NZS 3008 says the install method supports it, 4mm² can sometimes carry a smaller (~25A) oven — but check.

Storage hot water, 20A MCB. 2.5mm² T&E if the run is short, 4mm² for longer runs or to keep volt-drop headroom for the element.

Single-phase split-system, 16A MCB, condenser ~10m away. 2.5mm² is fine for the current, but if the inverter has high inrush you may bump to 4mm² to avoid nuisance tripping.

Sub-main to a detached garage, 50A, 35m run. 10mm² is the typical pick — sometimes 16mm² if the run is long or future-proofing for an EV charger.

Consumer mains, typical 80A single-phase home. 25mm² Cu (or equivalent aluminium). Sized to the supply authority's requirements and voltage drop from the pole to the meter, then meter to board.

These are starting points, not gospel — always check the install conditions and run the numbers for anything non-standard.

Voltage drop — rules of thumb

AS/NZS 3000 caps total voltage drop at 5% from the supply point to the point of use. Most sparkies work to:

• 3% on the final sub-circuit (point of common coupling to the load)
• 2% reserved for consumer mains + sub-mains

The rough formula:

Voltage drop (V) = (route length × current × mV/A/m) / 1000

You can pull the mV/A/m figure from AS/NZS 3008.1.1 Table 41. For single-phase Cu V90, the typical values are:

Cable size	Approx mV/A/m (single phase, Cu, V90)
1.0mm²	~44
1.5mm²	~29
2.5mm²	~18
4.0mm²	~11
6.0mm²	~7.3
10mm²	~4.4
16mm²	~2.8
25mm²	~1.75

Quick example: 2.5mm² lighting circuit, 10A load, 40m run. Drop = (40 × 10 × 18) / 1000 = 7.2V.

On 230V that's 3.1% — just over the 3% target for a final sub-circuit. Either accept it, knock the design current back, or step up to 4mm².

Common cable sizing mistakes we see

These come across the counter every week:

Sizing to the breaker, not the cable. The breaker is sized to protect the cable, not the other way round. Picking the breaker first, then choosing the cable to suit, can land you with an undersized cable on paper.

Ignoring derating. A cable bundled with four others in a conduit, or surrounded by thermal insulation in a roof, can lose 30–40% of its current rating. AS/NZS 3008 lists the derating factors. Use them.

Forgetting voltage drop on long runs. This is the most common reason a "correct" cable size fails its check. Anything over ~25m on a final sub-circuit deserves a quick volt-drop calc.

Mixing cable types on the same run. Splicing a piece of orange circular onto a length of TPS to make up a shortfall isn't legal and won't pass inspection. Buy the right length the first time — we stock 100m and 500m drums of every common size.

Not checking the installation method. "2.5mm carries 20A" is true sometimes. In other installation methods it carries 15A or less.

Order cable from ARCK

We stock the full range — 1mm, 1.5mm, 2.5mm, 4mm, 6mm, 10mm, 16mm, 25mm and up — in Twin & Earth, orange circular, single core, aluminium consumer mains, and three-phase. 100m and 500m drums on the shelf at our North Parramatta trade counter and same-day pick-up if you call before lunch.

Browse the full cable range, grab the matching circuit protection, or call the counter on (02) 9890 9693 if you want a hand sizing a tricky run. Mon–Fri 6:30am–5pm, Sat 7:30am–1pm.