Description

This report, which is Part V of the 69-30 series, provides current ratings for cables with 90°C thermosetting insulation. The ratings were calculated based on the dimensions of cables to BS 5467. Ratings are given for cables installed direct in the ground, in underground ducts and in air. These ratings are also considered to be applicable to cables to BS 6724, BS 7846 and BS 7889.

Ratings have been calculated in accordance with the formulae recommended by the International Electrotechnical Commission in their standard IEC 60287 and amendments 1 to 4 where relevant, and for other cases formulae have been taken from ERA reports. The conductor temperature limit of 90°C on which the cable ratings are based has been adopted to conform to the British Standards.

Ratings are given for single circuit configurations of either steel wire, aluminium wire or aluminium strip armoured cables. Tables of group rating factors for cables laid direct in the ground and in single way ducts have been omitted. However, the construction of the cables to the above standard differs to a small extent only from that of cables to BS 6346 so that group rating factors given in 69-30 Part III can be used as a guide. It is estimated that the error will, at worst, give group ratings not more than 1% on the high side.

An important warning relevant to this edition concerns guidance on the choice of soil thermal resistivity for cables laid in the ground, see Section 1.7.