3/29 vs 7/29 wire — which one goes where in house wiring?

What is the difference between 3/29 and 7/29 wire?

The code is strands times strand diameter, and the diameter is in inches — an imperial habit the Pakistani wire trade never dropped. So 3/29 is three strands of 0.029 inch and 7/29 is seven strands of 0.029 inch. The same strand, different count.

The arithmetic: 0.029 inch is 0.7366 mm. One strand's area is π/4 × 0.7366² = 0.426 mm². Three strands: 3 × 0.426 = 1.28 mm². Seven strands: 7 × 0.426 = 2.98 mm². The codes do not land exactly on the IEC 60228 nominal areas, which is why each wire has two names: 3/29 sells as 1.5 mm² even though it carries less copper than that, and 7/29 sells as 3 mm² — some shops bill it as 2.5–3 mm², because it sits between the two nominals.

In Pakistan's wire market, 3/29 and 7/29 are strand codes read as strands times diameter in inches: 3/29 means three copper strands of 0.029 inch, and 7/29 means seven strands of 0.029 inch. Three strands work out to 1.28 mm² of copper, sold as 1.5 mm² wire; seven strands work out to 2.98 mm², sold as 2.5–3 mm². On BS 7671 reference method C — clipped direct, 30°C, two loaded conductors — wire sold as 1.5 mm² is rated 19.5 A and wire sold as 2.5–3 mm² is rated 27 A. In a house on Pakistan's 220 V supply, 3/29 belongs on lighting and fan circuits behind a 6–10 A breaker, and 7/29 belongs on socket circuits behind a 16 A breaker. Neither code is the right wire for a 1.5 ton air conditioner or an electric geyser; those circuits start at 4 mm², confirmed by a licensed electrician.

Notice the shape of those numbers: 7/29 carries 7 ÷ 3 = 2.33 times the copper of 3/29, but 27 ÷ 19.5 is only about 1.4 times the current. Capacity does not scale with area, because a thicker conductor has proportionally less surface to shed its heat through. That is why doubling the strands never doubles the amps — and why the amp rating, not the copper weight, is what a circuit is sized on. 3/29 and 7/29 are two rungs of a longer ladder; the wire strand codes guide charts every code from 3/29 to 7/64 against its metric name.

3/29 or 7/29 for house wiring — which circuit gets which?

A house on a 220 V single-phase supply splits into circuits, and each circuit's wire is sized against its breaker, not against the appliance alone. That is the whole logic of the 3/29-or-7/29 choice:

• Lighting and fan circuits — 3/29. The usual lighting breaker in a Pakistani board is 6–10 A. A room's LED lights and ceiling fans together draw an amp or two; 3/29 at 19.5 A clears that breaker with margin to spare even after derating for conduit and summer heat. The LED lighting guide and ceiling fan guide cover those circuits in detail.
• Socket circuits — 7/29. Room sockets normally sit behind a 16 A MCB. 7/29 at 27 A keeps an 11 A margin over that breaker before derating. Keep it out of a conduit packed with other loaded circuits, and the margin holds.
• Never 3/29 on a socket circuit. Its 19.5 A rating looks like it clears a 16 A breaker — until conduit grouping and summer heat derate it below the breaker, and the cable cooks before the protection trips. If a shop hands you 3/29 for a socket circuit, hand it back.
• Dedicated appliance circuits — neither. AC, geyser and motor points get their own circuits and bigger wire; the next-but-one section says why.

For the whole-house scheme — how many circuits, which size on each, and the earthing to match — start from the best wire for house wiring guide and the SWG–mm² wire size chart.

How far can each wire run before voltage drop bites?

Heat sets the amp rating; length sets the second limit. Every metre of wire loses millivolts per amp, and on a long run that loss adds up at the far end. Two worked examples, using the mV/A/m figures from the table above.

A lighting circuit on 3/29: 5 A over a 20 m run drops 29 × 5 × 20 ÷ 1000 = 2.9 V. Hold the installation to 3% of 220 V — 6.6 V — and give the final circuit half of it, 3.3 V, because the submain from the meter has already spent the rest. 2.9 V passes.

A socket circuit on 7/29: 10 A over an 18 m run drops 18 × 10 × 18 ÷ 1000 = 3.24 V — just inside the same 3.3 V budget. Stretch the run to 25 m at the same 10 A and it becomes 18 × 10 × 25 ÷ 1000 = 4.5 V, well over budget: shorten the route, split the circuit, or go up a size.

On the 3.3 V budget, 3/29 at 5 A runs 3.3 ÷ 0.145 = 22 m and 7/29 at 10 A runs 3.3 ÷ 0.18 = 18 m. Most rooms sit inside those lengths; the far corner of a double-storey plot does not. Put your own current and route into the voltage drop calculator before you buy the coil.

When neither 3/29 nor 7/29 is the right wire

The two codes on this page cover lights and sockets, and that is where their job ends. Two circuits in a Pakistani house routinely get wired with 7/29 anyway, and both deserve better:

• The AC point. A 1.5 ton unit runs at about 8 A, but it sits on a 20 A type C breaker to ride the compressor's start surge, and the wire must clear that breaker after derating for conduit and summer heat. 7/29 is the size that runs out of margin first in that arithmetic. The 1.5 ton AC wire guide works it through and lands on 4 mm² — the code 7/36.
• The geyser point. A heating element pulls its full current for long, unbroken stretches — the hardest duty a house circuit sees. Size it from the geyser cable guide, on its own breaker, never off a socket circuit.

The shop will not always volunteer this: 7/29 is the answer to "socket ka wire", not to "AC ka wire". Ask by the circuit, not by the habit.

3/29 aur 7/29 mein kya farq hai?

3/29 ka matlab hai teen strand, har aik 0.029 inch ka — kul 1.28 mm² copper, jo bazaar mein 1.5 mm² ke naam se bikta hai. 7/29 mein wohi strand saat hote hain — 2.98 mm², jo 2.5–3 mm² ke naam se bikta hai. Ghar ki wiring mein 3/29 lights aur pankhon ke circuit par jata hai, 6–10 A breaker ke saath; 7/29 socket circuit par, 16 A breaker ke saath.

AC ya geyser ke liye dono chhote hain — wahan 4 mm² (7/36) ya us se bara wire chahiye, apne alag breaker par. Aur 3/29 kabhi socket circuit par na lagayen: garmi aur bhare conduit mein uski 19.5 A rating 16 A breaker se neeche aa jati hai, to wire pehle jalega aur breaker baad mein girega.

The wire behind each code

SINGLE CORE · STRANDED COPPER · 450/750 V PVC

3/29 and 7/29, drawn in Lahore

Both codes come off the Pilone line as single-core stranded copper, PVC insulated, 450/750 V — 3/29 copper cable for the lighting circuits, 7/29 copper cable for the sockets. Copper is priced by the day, so the current rate lives on the product page and the exact figure on WhatsApp.

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Send the codes, total metres per size and your city — delivery in Punjab takes 1–2 days, the rest of Pakistan 2–4.

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