4mm or 6mm cable? 36 A against 46 A, and the run that decides it

PILONE CABLES TECHNICAL TEAM

Stay on 4 mm² for a single appliance point on a 20 A or 25 A breaker. Step to 6 mm² when the circuit is a submain feeding several loads, when the breaker is 32 A, or when the run is long enough that 4 mm² spends its voltage budget.

4 mm² carries 36 A and 6 mm² carries 46 A, both clipped direct at 30°C — a 28% gain for 50% more copper. The bigger difference is voltage drop: 7.3 mV/A/m against 11, which stretches the same circuit half as far again. Length, not load, is usually what forces this step.

4mm vs 6mm cable, side by side

Copper conductors, PVC insulated, 450/750 V. Conductor resistance and strand construction per IEC 60228; current capacity and voltage drop per BS 7671, installation reference method C (clipped direct), 30°C ambient. Conductor copper mass computed at 8.89 kg/km per mm². Verify sizing with a licensed electrician for your installation.
Property	4 mm²	6 mm²
Standard (class 2) strands	7/0.85	7/1.04
Flexible (class 5) strands	56/0.30	84/0.30
Max resistance, class 2, 20°C	4.61 Ω/km	3.08 Ω/km
Capacity, 2 loaded cores	36 A	46 A
Capacity, 3 loaded cores	32 A	41 A
Voltage drop	11 mV/A/m	7.3 mV/A/m
Conductor copper	35.6 kg/km	53.3 kg/km
Trade code	7/.036	7/.044

Read the two-core row for a single-phase circuit and the three-core row for three-phase. How those capacity and voltage-drop figures are derived, and what the imperial trade codes compute to, is worked through on the 2.5mm vs 4mm cable guide — the method is identical one size up.

The jobs that justify the step to 6mm

6 mm² copper is not a general upgrade over 4 mm²; it is the size for circuits where either the total connected load or the run length has outgrown 36 A and 11 mV/A/m. On a 220 V single-phase supply that means a submain rather than a single appliance point, a 32 A breaker rather than a 20 or 25, or any circuit past roughly 25 metres at 25 A. A lone air conditioner, geyser or oven on its own way stays on 4 mm².

Stay on 4 mm² for one AC point, one geyser, one oven or hob, or a kitchen circuit on a 20 A or 25 A breaker within about 25 metres of the board.
Take 6 mm² for the submain to an upper-floor or annexe board, a circuit feeding an AC and a geyser together, a motor or pump run of any length, or anything protected at 32 A.
Take 6 mm² on length alone when the arithmetic below says 4 mm² is over budget, even if the current is well inside 36 A. This is the commonest reason to step up and the one most quotes miss.
Go past 6 mm² once you are feeding a whole board from the meter. That is 10 mm² at 63 A or 16 mm² at 85 A, covered in the main meter cable guide.

Where 4mm runs out of length

Take a submain carrying 30 A to a first-floor board, 25 metres of route from the main board. On 4 mm² the loss is 11 × 30 × 25 ÷ 1000 = 8.25 V, which is 3.75% of 220 V — past the 3% the installation is normally held to, and that is before the final circuits upstairs spend anything of their own. On 6 mm² it is 7.3 × 30 × 25 ÷ 1000 = 5.48 V, or 2.5%, which leaves headroom for the circuits beyond it.

Longest one-way run that stays inside a 6.6 V budget, which is 3% of a 220 V supply. Length = 6.6 ÷ (mV/A/m ÷ 1000 × current). A submain should be given only part of that budget, because the circuits it feeds spend the rest. Voltage drop per BS 7671, reference method C, 30°C, copper, PVC. Verify sizing with a licensed electrician for your installation.
Load	4 mm²	6 mm²
20 A	30.0 m	45.2 m
25 A	24.0 m	36.2 m
30 A	20.0 m	30.1 m
32 A	18.8 m	28.3 m

6 mm² buys 1.51 times the run of 4 mm² at every load, because 11 ÷ 7.3 = 1.51. Put your own current and route length into the voltage drop calculator before ordering.

Current capacity depends on how the cable is installed. Derate for conduit, grouping and ambient temperature above 30°C, and take the correction factors for your own method from BS 7671. Have a licensed electrician confirm the size for your load and run length — or start with the cable size calculator.

What the step costs in copper

Cable is priced off the day's copper rate, so compare the two sizes by their metal rather than by a rupee figure that goes stale. 4 mm² holds 35.6 kg of copper per kilometre of conductor and 6 mm² holds 53.3, so 53.3 ÷ 35.6 = 1.5. The step up costs half as much copper again per core, on the same length, and returns 10 A of capacity and 51% more reach. On a 25 m submain of three cores that is 25 × 3 × (0.0533 − 0.0356) = about 1.3 kg of extra copper for the whole job. Send the metres and your city and we will quote both sizes in one message.

The cable for each job

4MM² · 2 CORE · CU CLASS 2

4mm 2 Core Standard Cable

7/0.85 class 2 copper, 4.61 Ω/km at 20°C, rated 36 A clipped direct at 30°C. One appliance point per way. Three-core version: 4mm 3 core standard cable.

Factory-direct price

Contact for quote

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6MM² · 2 CORE · CU CLASS 2

6mm 2 Core Standard Cable

7/1.04 class 2 copper, 3.08 Ω/km at 20°C, rated 46 A clipped direct at 30°C. Submains, motors and long runs. Three-core version: 6mm 3 core cable price.

Factory-direct price

Contact for quote

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Cable tracks the daily copper rate, so we quote per metre and per coil on WhatsApp. Where the tail has to bend at a motor or a machine, take the flexible build instead: 6mm 3 core flexible cable.

Frequently asked

Is 6mm cable worth it over 4mm for a house?

Only on the submains. Inside a house the appliance circuits sit on 4 mm² and the sockets and lights on smaller sizes; 6 mm² earns its place feeding an upper-floor board, a pump, or a circuit carrying two heavy appliances. Upsizing every circuit to 6 mm² buys reach nobody uses and costs half as much copper again per metre.

4mm ya 6mm — geyser aur AC ek hi line par hon to kaun sa?

Behtar yeh hai ke dono ke alag alag circuit hon, har ek 4 mm² par apne breaker ke saath. Agar ek hi submain dono ko feed karti hai, to 6 mm² lein — 46 A capacity aur 7.3 mV/A/m drop, taake dono ek waqt mein chalen to bhi voltage theek rahe. Run 25 meter se lamba ho to 6 mm² hi lein.

How far can 4mm cable run before I need 6mm?

On a 6.6 V budget, which is 3% of 220 V: 30 m at 20 A, 24 m at 25 A, 20 m at 30 A. 6 mm² reaches 1.51 times as far at the same current. Measure the route the cable takes, and give a submain only part of the budget because the circuits beyond it spend the rest.

Does a bigger air conditioner need 6mm instead of 4mm?

Not usually. Household split units up to 2 ton sit comfortably on 4 mm² on their own 20 A or 25 A breaker, because the running current is well under 36 A. 6 mm² comes in when the run is long or one circuit feeds more than one unit. Tonnage by tonnage, see the AC wire size chart.

Is 6mm the same as 7/.044?

7/.044 is what the Pakistani trade sells as 6 mm². Seven strands of 0.044 inch is seven strands of 1.118 mm, which computes to 6.87 mm² of copper, and the market prices and labels it as 6 mm². The figure that settles fitness is resistance: IEC 60228 caps 6 mm² class 2 at 3.08 ohm/km.

4mm and 6mm cable at the factory rate

Send the load, the route length and your city, and we will size it and quote both. Drawn in Lahore, sold at the day's copper rate: Punjab in 1–2 days, rest of Pakistan in 2–4.

WhatsApp for both rates