IEC 60502 vs GB/T 12706 vs BS 7870: XLPE Power Cable Standards Compared
Three standards sit behind almost every XLPE insulated power cable enquiry we receive: IEC 60502, GB/T 12706 and BS 7870. They are technically close relatives, but the differences in voltage designation, test regime and conductor class decide whether an inspection certificate is accepted at site. This article sets out what actually differs.
Why the Standard Matters More Than the Datasheet
Two suppliers can both quote "0.6/1 kV copper XLPE cable" and deliver products that fail different tests. One may be built to GB/T 12706.1 with a 0.7 mm insulation wall and a routine spark test; the other to IEC 60502-1 with a full 3.5 kV / 5 min routine voltage test and a 4-hour sequential test on samples. The purchase order must name the standard and the edition.
Side-by-Side Comparison
| Item | IEC 60502-1 / -2 | GB/T 12706.1 | BS 7870 |
|---|---|---|---|
| Scope | 1 kV to 30 kV extruded insulation | 1 kV to 35 kV, aligned with IEC | LV distribution cables for UK networks |
| Voltage designation | U0/U (Um) | U0/U (Um) | U0/U, 0.6/1 kV typical |
| Conductor class | Class 1 solid, Class 2 stranded per IEC 60228 | Class 1 and Class 2, same tables | Class 2 compacted, waveform specific |
| Sheath compound | ST1 / ST2 / ST3 / ST7 | ST1 / ST2 equivalent | PE or PVC per UK practice |
| Routine voltage test | 3.5 kV / 5 min (0.6/1 kV) | 3.5 kV / 5 min | 3.5 kV / 5 min |
| Acceptance in projects | Global, World Bank and ADB tenders | China, Southeast Asia, Africa, Middle East | UK DNO and utility frameworks |
Voltage Designation: U0/U (Um)
IEC and GB both express the rating as U0/U, where U0 is the phase-to-earth voltage and U the phase-to-phase voltage. A cable marked 0.6/1 (1.2) kV therefore means 0.6 kV to earth, 1 kV between phases and 1.2 kV maximum system voltage. Medium-voltage designs continue as 3.6/6, 6/10, 8.7/15, 12/20 and 18/30 kV. Confusing U0 with U is the single most common specification error we correct for buyers.
Test Regime: What the Buyer Actually Receives
- Routine tests on every drum — conductor resistance, partial discharge for MV, and the 3.5 kV / 5 min voltage test for LV.
- Sample tests on finished cable — conductor examination, insulation and sheath dimensions, tensile and elongation before and after ageing.
- Type tests once per design — electrical ageing, impulse voltage for MV, and the 4-hour AC test at elevated voltage.
Buyers should ask for the routine test certificate per drum and the type test report for the cable design, not for a generic catalogue page.
Where the Standards Genuinely Differ
- Insulation thickness tables are close but not identical for sizes below 16 mm²; a GB/T builds 0.7 mm where some IEC editions allow 0.6 mm.
- Sheath colour and marking — BS 7870 practice expects specific UK marking sequences and waveform conductors.
- Flame test — IEC 60332-1 or -3 versus BS EN 60332 equivalents; the wording in the PO determines the test house.
- Armour construction — steel tape for LV direct burial versus steel wire for MV and for larger fault currents.
Practical Recommendation
For projects outside the United Kingdom, specify IEC 60502-1 or -2 as the primary standard and add GB/T 12706.1 as an acceptable equivalent for factory routine testing. Add KEMA or TUV type test reports where the lender or consultant requires independent verification, and state explicitly whether CE marking and a Declaration of Performance are needed.
For construction details, designations and current rating tables of the same cable family, see the XLPE insulated power cable guide.
