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IEC 60228 (Conductors)
IEC 60228 (Conductors)
IEC 60228 conductors are defined under the IEC 60228:2023 standard, which specifies the nominal cross-sectional areas for conductors used in electric power cables and cords, ranging from 0.5 mm² to 3,500 mm². This standard applies to various types of IEC 60228 conductors, including solid, stranded, and Milliken conductors made from copper, aluminum, and aluminum alloys. It also includes flexible copper IEC 60228 conductors designed for fixed cable installations. However, the IEC 60228 standard for conductors does not cover applications intended for telecommunication purposes.
1. Why IEC 60228 matters
Inside every power, control, or data cable are IEC 60228 conductors, which determine how much current can flow, how much heat is generated, and how long the cable will last. The IEC 60228 standard, titled “Conductors of insulated cables”, is the foundational document specifying how IEC 60228 conductors must be constructed and the direct-current (d.c.) resistance they must meet at 20 °C. Recognized globally, this standard for IEC 60228 conductors is referenced by nearly every major cable regulation, including IEC 60502, IEC 60332, EN 50575/CPR, BS 6724, and NF C 32-322. As a result, a single certification for IEC 60228 conductors allows cable specifiers to source compliant cables internationally without needing to retest under local conductor standards.
2. Scope in one sentence
IEC 60228 conductors, as defined in the IEC 60228:2023 standard, include solid, stranded, flexible, and extra-flexible types made from copper, aluminium, or aluminium alloy. These IEC 60228 conductors are manufactured in cross-sectional areas ranging from 0.5 mm² to 3,500 mm² and are commonly used in power and control cables for both fixed and flexible installations. The standard for IEC 60228 conductors ensures consistent performance across various cable applications. However, IEC 60228 conductors do not cover use in telecommunication, RF systems, or bare overhead conductors.
3. Edition history & what changed in 2023
| Edition | Year | Key changes |
| 1st | 1968 | First alignment of metric cross-sections and resistance values. |
| 2nd | 1978 | Added aluminium and tinned copper resistance tables. |
| 3rd | 2004 (still cited by many national specs) | Introduced Class 5 and Class 6 flexibility definitions. |
| 4th | 2023 |
• Extended nominal areas to 3 500 mm² • Added Milliken sector conductors • Tightened resistance tolerances for aluminium-magnesium-silicon alloys • Clarified test‐equipment accuracy (ref IECEE OD-5014). cdn.standards.iteh.aicdn.standards.iteh.ai |
Always specify the edition year when referencing IEC 60228 conductors on drawings and RFQs—for example, “IEC 60228:2023 Class 2 Cu conductors”—to ensure you receive IEC 60228 conductors built to the latest standards, avoiding outdated 2004 tolerances with looser requirements.
4. Conductor classes – the heart of the standard
| Class | Typical construction | Flexibility index* | Typical cable types |
| 1 – Solid | Single, round or sector copper/aluminium wire | ★ | Building wires (H07V-U), transformer windings |
| 2 – Stranded | 7, 19, 37, 61 or 127 wires, compacted or non-compacted | ★★ | LV & MV power cables (IEC 60502-1/-2), control cables |
| 5 – Flexible |
Very fine strands ≤ 0.21 mm for 0.5–6 mm²; ≤ 0.41 mm above 6 mm² |
★★★★ | H05VV-F cords, drag-chain automation cables |
| 6 – Extra flexible | Finer strands (≤ 0.16 mm up to 4 mm²; ≤ 0.25 mm above) | ★★★★★ | Welding leads, speaker cables, robotics dress-packs |
*Higher stars = greater strand count → smaller wire Ø → tighter bend radius allowed.
Milliken and segmental conductors (used above 1 000 mm² to cut skin-effect losses) are now explicitly recognised as Class 2 variants provided each sector meets the strand rule.
5. Resistance tables – the compliance benchmark
| Nominal area (mm²) | Class 1/2 (Ω /km) | Class 5 (Ω /km) | Class 6 (Ω /km) |
| 1.5 | 12.1 | 13.3 | 13.7 |
| 10 | 1.83 | 1.91 | 1.94 |
| 120 | 0.153 | 0.158 | 0.161 |
Values factor in strand lay-length and contact resistance; manufacturers must not exceed them after compaction or tinning.
Why it matters:
- Energy efficiency – a 120 mm² Cu feeder that runs 5 % above spec adds ~200 W loss per 100 m at 250 A.
- Temperature rise – incorrect resistance shortens insulation life or triggers breaker nuisance trips.
6. Material options and treatments
| Material | Resistivity ρ (20 °C) | Notes |
| Annealed copper | 1.724 µΩ cm (the reference) | Preferred for class 5/6 because of ductility. |
| Tinned copper | +2 % resistance allowance | Tin eases soldering and slows corrosion in LSZH cables. |
| Aluminium (1xxx) | 2.826 µΩ cm | 48 % lighter than Cu; needs larger cross-section. |
| Al-Mg-Si alloy | 3.086 µΩ cm (tightened in 2023) | Higher strength for overhead style cores in hybrid cables. |
7. Manufacturing tolerances & checks
| Clause | Test | Acceptance criteria |
| 6.2 | Number & diameter of wires | Micrometer on 10 % sample strands; each Ø within +/- 3 %. |
| 6.4 | Overall conductor diameter | Within ±5 % of tabulated max. |
| 7.2 | d.c. resistance | ≤ table value after any compaction & heat treatment. |
| 7.3 | Tensile test on individual wires | Cu: ≥ 200 MPa Rm; Al: ≥ 125 MPa. |
| 7.4 | Elongation | Cu ≥ 20 % (1 & 2); Cu ≥ 15 % (5 & 6); Al ≥ 4 %. |
| 7.5 | Hot set (for tinned copper) | ≤ 10 % set at 150 °C, 20 N cm-². |
Factories run routine resistance checks on every reel, while tensile/elongation are sample tests per production lot.
8. How IEC 60228 plugs into the bigger cable rulebook
- Dimensional core: IEC 60502 uses the nominal areas and classes from 60228 to define insulation thickness (e.g., 10 mm² Class 2 Cu → 3.4 mm XLPE @ 0.6/1 kV).
- Fire standards: CPR/EN 50575 Euroclass calculations reference conductor heat capacity, which in turn relies on 60228 copper mass.
- Short-circuit rating: IEC 60949 formula Isc = k × S takes S (area) straight from 60228 tables.
- Ampacity: IEC 60287 loss equations assume the resistance ≤ 60228 limit; overshoot would invalidate derating curves.
9. Comparing IEC 60228 metric sizes with AWG/MCM
| IEC size (mm²) | Nearest AWG | Resistance Cu Ω/km (IEC) | Difference vs IEC limit |
| 2.5 | 14 | 7.35 |
AWG table gives 8.29 Ω/km → worse (⚠ higher loss) |
| 16 | 6 | 1.15 | AWG 6 = 1.31 Ω/km → still higher |
| 95 | 3/0 | 0.193 | AWG 3/0 = 0.206 Ω/km → close |
10. Specifiers’ mini-guide (print & pin)
- State the edition – “IEC 60228:2023”.
- Pick the class – 1/2 for fixed; 5 for flexible; 6 for robotics.
- Material – plain Cu, tinned Cu, Al, or Al alloy.
- Nominal area – 0.5 … 3 500 mm²; beware AWG mismatches.
- Shape – circular, sector, compacted circular, Milliken.
- Resistance clause – “shall not exceed Table 1 values”.
- Certificate – request type-test report ≤ 5 years old & routine resistance log for each delivery.
11. Emerging trends & likely future amendments
- Carbon-footprint disclosure – WG 9 has proposed Annex E requiring kg CO₂ e per tonne conductor, aligned with ISO 14067.
- High-temperature alloys – trial tables for CuMg and Al-Zr conductors rated 105 °C continuous are under committee review.
- Recycled copper verification – draft method links conductivity scatter to trace elements, ensuring scrap blends still hit R20 limits.
- Digital nameplates – Edition 5 may mandate a QR code on drum flange linking to resistance & tensile batch data.
11. Emerging trends & likely future amendments
Yes, the standard allows mixed classes provided each core meets its own resistance row and overall lay remains symmetrical.
Tin adds ≈ 2 % resistance—already factored into the tinned-copper rows—so derating is not required if tables are met.
IEC 60228 sets maximum resistance; compaction is optional unless another standard (e.g., IEC 60502 for 35 kV) requires it to control electric-field stress.