IEC 60228 Conductor
Classes Explained.
Class 1, 2, 5, 6 — these are not quality grades. They are construction classes that define flexibility, strand count, and wire diameter. Specifying the wrong class in a panel causes cable failures that look like terminal problems. This is the definitive reference.
What each conductor class means.
Strand count and resistance by class — IEC 60228 / IS 8130:2013.
| Size (mm²) | Class 1 — solid | Class 2 — stranded | Class 5 — flexible | Max R Class 2 (Ω/km) | Max R Class 5 (Ω/km) |
|---|---|---|---|---|---|
| 0.5 | 1 solid wire | — | 16 × 0.20mm | 36.0 | 39.0 |
| 0.75 | 1 solid wire | — | 24 × 0.20mm | 24.5 | 26.0 |
| 1.0 | 1 solid wire | — | 32 × 0.20mm | 18.1 | 19.5 |
| 1.5 | 1 solid wire | 7 × 0.52mm | 30 × 0.25mm | 12.1 | 13.3 |
| 2.5 | 1 solid wire | 7 × 0.67mm | 50 × 0.25mm | 7.41 | 7.98 |
| 4.0 | — | 7 × 0.85mm | 56 × 0.30mm | 4.61 | 4.95 |
| 6.0 | — | 7 × 1.04mm | 84 × 0.30mm | 3.08 | 3.30 |
| 10.0 | — | 7 × 1.35mm | 80 × 0.40mm | 1.83 | 1.91 |
| 16.0 | — | 7 × 1.70mm | 128 × 0.40mm | 1.15 | 1.21 |
| 25.0 | — | 7 × 2.14mm | 200 × 0.40mm | 0.727 | 0.780 |
Source: IEC 60228:2004 Table 1–3 / IS 8130:2013. Strand counts are typical minimum — manufacturers may use more strands of smaller diameter.
The work-hardening failure mode — why Class 5 is not optional.
Class 1 (solid) and Class 2 (stranded) conductors are designed for fixed installation. Once routed in conduit or wall, they are static. Inside a switchgear panel, every conductor is routed through multiple bends during installation and disturbed for maintenance.
Repeated bending of a solid or Class 2 conductor causes work-hardening — the copper becomes progressively more brittle until it fractures at a termination point. The fracture is invisible on visual inspection. The failure presents as intermittent high-resistance contact, unexpected tripping, or terminal overheating — not as an obvious broken wire.
Class 5 fine-stranded conductors distribute bending stress across many small strands. Each strand bends elastically. No single strand accumulates enough plastic deformation to fracture under normal installation and maintenance conditions. This is the engineering reason IS 8130:2013 Class 5 is specified for panel and flexible cable — not preference.
Building fixed wiring in conduit: Class 2 stranded is common in the market (IS 8130:2013). National Cables FR Single Core Wire (IS 694:2010) is supplied as Class 5 standard for pull-through flexibility; Class 2 and Class 1 on request.
Panel internal wiring, OEM equipment: Class 5 fine-stranded (IS 8130:2013 / IS 694:2010 Single Core Flexible)
Trailing leads, moving machinery: Class 5 or Class 6 (IS 694:2010 / IEC 60245 flexible cord)
Control cable, multicore: Class 5 (IS 694:2010 Control Cable / Multicore Flexible)
IS 8130:2013 — the Indian equivalent of IEC 60228.
IS 8130:2013 is the Bureau of Indian Standards specification for conductors of insulated cables. It is technically harmonised with IEC 60228:2004. The class designations — 1, 2, 5, 6 — are identical. The resistance values are the same. When IS 694:2010 specifies "conductor to IS 8130:2013," this means IEC 60228 requirements are met.
The practical implication for procurement: a cable marketed as "IS 8130:2013 Class 2" meets the same conductor specification as "IEC 60228 Class 2." Test certificates from IS 8130:2013 and IEC 60228 are equivalent for conductor resistance verification.
Conductor classes — common engineering questions.
Why the conductor class on the spec sheet matters more than the cross-section, and what happens when the wrong class is used.
Why is Class 5 specified for panel wiring instead of Class 2?
Class 2 (stranded) conductors are designed for fixed installation in conduit, on a wall, or in a duct — they remain static after routing. Class 5 (fine-stranded) is designed for flexible applications and panel wiring because the many thin individual strands distribute bending stress elastically. Each strand flexes without work-hardening.
Inside a switchgear panel, every conductor is bent multiple times during installation, and again during maintenance. Repeated bending of Class 2 progressively work-hardens the larger strands until they fracture at a termination point. The fracture is invisible from outside and presents as intermittent contact, unexpected tripping, or terminal overheating — not as an obviously broken wire. Class 5 is the engineering requirement, not preference.
Can I substitute Class 2 for Class 5 in a flexible application?
No. IEC 60228:2004 and IS 8130:2013 assign each class to a specific application context. Class 2 is for fixed building wiring; Class 5 is for flexible and panel applications.
Substituting Class 2 where Class 5 is specified — for example, in trailing leads, control panel internal wiring, or any cable subject to repeated installation/maintenance disturbance — causes work-hardening failures because the individual strands are too thick to flex elastically. The cable's certification is to a specific class; using it outside its design context voids the compliance claim.
What happens if I use a solid Class 1 conductor in a flexible application?
Solid Class 1 has zero flexibility. Used in any flexible context — panel wiring, trailing leads, moving equipment — the single solid wire cannot distribute bending stress and rapidly work-hardens, fracturing at a termination or splice. Failures typically present within months of service as intermittent contact faults rather than obvious breakage, making them difficult to diagnose.
IEC 60228 and IS 8130:2013 reserve Class 1 strictly for permanent fixed installation in building wiring (in conduit or buried in walls) where the conductor will not be disturbed after installation.
How do I verify a cable meets IS 8130:2013 Class 5 requirements?
IS 8130:2013 is technically harmonised with IEC 60228:2004 — identical class designations (1, 2, 5, 6) and identical maximum resistance values. A cable certified to IEC 60228 Class 5 automatically meets IS 8130:2013 Class 5.
Verify by checking the supplier's test certificate: it should state the conductor class and the maximum DC resistance in Ω/km at 20°C. The resistance value must not exceed the standard's table for that class and cross-section. Strand counts on the page are typical minimums — manufacturers may use more strands than the minimum, but never fewer. Always request the test certificate from your supplier; it is the proof of class compliance.
Need Class 5 flexible wire or Class 2 building wire?
National Cables manufactures both — IS 694:2010 certified, BIS marked.