Flexible, stranded or solid? What the strand count really changes

PILONE CABLES TECHNICAL TEAM

Take flexible — IEC 60228 class 5 — for anything pulled through conduit, terminated in a panel, or connected to something that moves. Take standard — class 2 — for a fixed run made once and left in a wall.

The size does not change with the build. 4 mm² is 36 A clipped direct at 30°C whether it is 7/0.85 class 2 or 56/0.30 class 5. What changes is how far the conductor bends before it fatigues, how it behaves in a screw terminal, and a small resistance penalty: IEC 60228 allows class 5 between 4% and 10% more resistance than class 2 at the same nominal size.

Three builds, not two

The question is usually asked as flexible versus solid, but a Pakistani shop sells three things and only calls two of them by name.

Solid is one single wire, class 1 in the standard. It exists only at the small sizes — a lighting drop, a loop inside a box. Bend it repeatedly and it work-hardens and snaps, so nothing heavy is sold this way.
Standard is what the counter means by "standard cable": class 2, a few thick strands, seven of them at every size up to 25 mm². Stiff enough to hold a shape, cheap to draw, and the normal choice for concealed fixed wiring.
Flexible is class 5: dozens of fine strands making the same cross-section. 2.5 mm² is 50 strands of 0.25 mm against 7 of 0.67 mm. It turns a corner in conduit without fighting back and survives being moved.

So what a Pakistani buyer is actually choosing between is the two stranded builds, not stranded against solid. Both hold copper of the same nominal size; the ladder below is the whole difference between them.

Class 2 and class 5, size by size

Strand construction and maximum conductor resistance per IEC 60228: class 2 (rigid stranded, sold as standard) against class 5 (flexible). Strand format is count / strand diameter in mm; resistance is the standard's maximum for a plain annealed copper conductor at 20°C. Current capacity is read against the nominal size and is the same for both classes: two loaded conductors, BS 7671 reference method C (clipped direct), 30°C ambient, PVC. Verify sizing with a licensed electrician for your installation.
Size	Class 2 strands	Class 5 strands	Class 2 resistance	Class 5 resistance	Capacity, 2 cores
1.5 mm²	7/0.53	30/0.25	12.1 Ω/km	13.3 Ω/km	19.5 A
2.5 mm²	7/0.67	50/0.25	7.41 Ω/km	7.98 Ω/km	27 A
4 mm²	7/0.85	56/0.30	4.61 Ω/km	4.95 Ω/km	36 A
6 mm²	7/1.04	84/0.30	3.08 Ω/km	3.30 Ω/km	46 A
10 mm²	7/1.35	80/0.40	1.83 Ω/km	1.91 Ω/km	63 A
16 mm²	7/1.70	126/0.40	1.15 Ω/km	1.21 Ω/km	85 A

Two things to read off it. The class 2 column is seven strands the whole way up, getting thicker as the size grows; the class 5 column changes both count and strand diameter — 10 mm² uses 80 strands of 0.40 mm where 6 mm² uses 84 of 0.30 mm, because past a point it is thicker strands, not more of them, that keep the conductor buildable. And the capacity column has one value per row, not two: the current rating belongs to the nominal size, not to the build.

What the extra strands cost you

Nobody publishes this and it is the one real electrical difference. IEC 60228 sets a higher maximum resistance for a class 5 conductor than for a class 2 conductor of the same nominal area — 7.98 against 7.41 Ω/km at 2.5 mm², 4.95 against 4.61 at 4 mm². The reason is geometry: fine strands are laid in a helix, so each strand is a little longer than the cable it runs through, and that extra length is extra resistance.

Put a number on it. A 4 mm² circuit carrying 20 A over a 30 m one-way run loses 2 × 20 × 30 × 4.61 ÷ 1000 = 5.53 V in class 2 and 2 × 20 × 30 × 4.95 ÷ 1000 = 5.94 V in class 5, both at 20°C. The flexible build costs you 0.41 V on that run — under a fifth of one percent of a 220 V supply. Real, measurable, and almost never the thing that decides a job. Both figures rise together once the conductor is working hot, which is where the tabulated 11 mV/A/m for 4 mm² comes from; that arithmetic is set out on the 2.5mm vs 4mm cable guide.

The honest summary: choose the build for how the cable has to be installed and handled, and check the length in the voltage drop calculator if the run is long enough for a fraction of a volt to matter.

Which build for which job

Both builds are available at the same nominal sizes, so the size decision is unchanged — take it from the load and the run length, then pick the build from this table.
Job	Build	Why
Pulling through conduit with several bends	Flexible, class 5	Turns corners without fighting the draw wire
Appliance tails, machine leads, pump connections	Flexible, class 5	The only build that tolerates repeated movement
Distribution board and panel wiring	Flexible, class 5	Tight radii inside an enclosure
Concealed fixed wiring, chased and plastered	Standard, class 2	Run once and left; cheaper for the same copper
Submains and meter tails on a straight route	Standard, class 2	Stiffness helps at a lug; fewer strands to clamp
Buried or exposed outdoor runs	Armoured, either class inside	Mechanical protection is a separate decision

The termination is where flexible goes wrong

A class 2 conductor has seven thick strands and a screw terminal clamps all seven. A class 5 conductor at the same size has fifty or more, and a screw driven onto loose fine strands pushes some of them aside instead of gripping them. Fewer strands then carry the whole current, the joint runs warm, and warm joints loosen as they heat and cool. This is the commonest fault in flexible wiring and it has nothing to do with the cable.

Crimp a bootlace ferrule on the end before it goes into a screw terminal. The ferrule turns the strands into one solid pin.
Never tin the end with solder as a substitute. Solder creeps under pressure and the joint loosens over time.
Do not lose strands during stripping. A conductor missing a fifth of its strands is a conductor a fifth undersized at that point.
At a lug, use one made for the strand class and crimp it with the right tool, not with pliers.

The current capacity in the table 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, the build and the terminations for your job — or start with the cable size calculator.

The cable for each build

FLEXIBLE · CLASS 5 · 450/750 V

Flexible Cable, All Sizes

Fine-stranded class 5 copper to IEC 60228, drawn in Lahore. The house-wiring sizes are 2.5mm 3 core flexible cable and 4mm 3 core flexible cable; for machine and pump tails, 6mm 3 core flexible cable.

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STANDARD · CLASS 2 · 450/750 V

Standard Cable, All Sizes

Seven-strand class 2 copper to IEC 60228 for fixed concealed wiring. Common picks are 4mm 3 core cable for appliance circuits and 16mm 2 core cable price for meter tails and submains.

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Both builds hold the same copper per metre at the same nominal size, so the rate difference between them is small — it is drawing cost, not metal. Send the size, the metres and your city and we will quote both against each other.

Frequently asked

What is the difference between flexible and solid cable?

The number of strands in the conductor. Solid is one wire. Standard is class 2, a few thick strands — 7/0.67 at 2.5 mm². Flexible is class 5, many fine strands — 50/0.25 at the same size. All three can be the same nominal cross-section and carry the same tabulated current; what changes is how far the conductor bends before it fatigues.

Does flexible cable carry less current than standard cable?

No. Capacity is read against the nominal size, so 4 mm² is 36 A clipped direct at 30°C in either build. IEC 60228 does allow class 5 a slightly higher resistance for the same size — 4.95 against 4.61 ohm/km at 4 mm², about 7 percent — because the fine strands are laid in a helix and each one is a little longer than the cable. On a long run that is worth knowing.

Flexible ya standard — ghar ki wiring ke liye kaun sa behtar hai?

Deewar ke andar conduit mein pull karne ke liye flexible aasan rehta hai, khaas taur par jahan mor zyada hon. Jo run ek dafa daal kar chhor dena hai, us par standard class 2 theek hai aur sasta bhi. Size dono mein wohi rakhein — 4 mm² dono soorat mein 36 A hai. Motor, machine ya appliance ki tail hamesha flexible.

Can I use flexible cable for permanent house wiring?

Yes, and in Pakistan it is common — flexible copper is pulled through conduit in most house rewires because it turns corners easily. The condition is the termination: fine strands must be clamped by the whole conductor, not pinched by a screw that splays half the strands out of the terminal. Use a ferrule or a proper clamp connector.

Why do fine strands need a ferrule in a screw terminal?

Because a screw bearing on 50 loose strands pushes some aside instead of clamping them all. Fewer strands carry the current, the joint runs warm, and it loosens as it heats and cools. A bootlace ferrule crimped on the end turns the strands into one solid pin the screw can hold. Standard class 2, with seven thick strands, is far more forgiving.

Is solid wire better than stranded for house wiring?

Only at the small sizes and only for short, straight, fixed runs — a lighting drop or a loop inside a box. Solid conductors are stiff, work-harden and break where they are flexed repeatedly, which is why nothing above the smallest sizes is sold solid. For a house rewire in Pakistan the real choice is class 2 against class 5.

Class 5 or class 2, at the factory rate

We draw both builds in Lahore and sell at the day's copper rate — no dealer margin, and the line that made the coil answers the message. Send the size, the metres and your city: Punjab in 1–2 days, rest of Pakistan in 2–4.

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