IEC 60364 Table B.52: Cable Current Ratings

Table B.52 in IEC 60364-5-52 (Annex B) provides the current-carrying capacity of cables installed according to the reference installation methods defined in Table B.52.1. It is the international equivalent of BS 7671 Tables 4D1A–4D5A and forms the basis for cable sizing in countries that adopt IEC standards directly.

The table series covers:

• Table B.52.2: Current ratings for PVC insulated cables (maximum conductor temperature 70°C)
• Table B.52.3: Current ratings for XLPE insulated cables (maximum conductor temperature 90°C)
• Table B.52.4: Current ratings for mineral insulated cables

All values are calculated under reference conditions: 30°C ambient air temperature, 20°C ground temperature, soil thermal resistivity of 2.5 K·m/W, and a single loaded circuit. When actual conditions differ, correction factors from Tables B.52.14 through B.52.21 must be applied.

IEC 60364-5-52 defines reference installation methods using an alphanumeric code system. Each method represents a specific physical arrangement with characteristic heat dissipation properties:

These method codes are shared with BS 7671 (which is derived from IEC 60364), making cross-referencing between the two standards straightforward. However, the specific current rating values may differ slightly due to differences in cable constructions covered by each standard.

The following table shows current-carrying capacity values for copper conductors with PVC insulation (70°C) in two-loaded-conductor configurations under IEC reference conditions:

Note: For three-phase circuits with three loaded conductors, the values differ slightly. The table above shows the two-loaded-conductor (single-phase or DC) configuration. Always verify which conductor loading applies to your circuit.

XLPE (cross-linked polyethylene) insulated cables operate at a maximum conductor temperature of 90°C compared to 70°C for PVC, giving them significantly higher current-carrying capacity for the same cross-sectional area:

The advantage of XLPE increases with cable size because larger cables are more thermally constrained. For cables above 50 mm², XLPE provides approximately 25% more capacity — which can mean a reduction of one or two cable sizes compared to PVC, often offsetting the higher material cost.

Installation methods D1 (in ducts in the ground) and D2 (direct buried) have their own current rating tables because heat dissipation in soil depends on factors not present in above-ground installations:

• Soil thermal resistivity: Reference value 2.5 K·m/W. Dry sandy soil may have 3.0+ K·m/W (poorer), while moist clay may have 1.0 K·m/W (better). Correction factors are in Table B.52.16.
• Depth of laying: Deeper cables have poorer heat dissipation. Standard reference depth is 0.7 m for ducts and 0.5–0.8 m for direct burial.
• Ground temperature: Reference value 20°C. Correction factors for other temperatures are in Table B.52.15.

Direct-buried cables (Method D2) generally have higher ratings than cables in ducts (Method D1) because the cable is in direct thermal contact with the surrounding soil, providing better heat transfer. However, direct burial makes future cable replacement more difficult and provides less mechanical protection.

BS 7671 Appendix 4 is directly derived from IEC 60364-5-52 Annex B, so the table structures and installation method codes are identical. The main differences are:

• Cable types: BS 7671 includes UK-specific cable constructions (flat twin-and-earth, mineral-insulated copper cables) not found in IEC 60364.
• Table numbering: IEC uses B.52.x (e.g., B.52.2), while BS 7671 uses 4Dxx (e.g., 4D1A). The mapping is systematic but not always one-to-one.
• National deviations: Some countries that adopt IEC 60364 apply national annexes with different values for specific cable types or conditions.

For standard cable types (PVC and XLPE, copper and aluminium), the current rating values in IEC 60364 Table B.52 and the corresponding BS 7671 tables are identical or very close, reflecting their shared technical basis.