For currents of 200 A and above, voltages up to 275 kV. Busbars of copper or aluminium, with principal insulation; air, oil, solid, semi-solid materials, primarily for a.c. power switchgear; but applicable in part to d.c. busbars, and to similar a.c. and d.c. connections between items not switchgear. Current ratings based on temperature rise above ambient; clearances for different types in detail; no cross-sectional dimensions. Appendices on: information on selection, temperature measurement, insulati on co-ordination, jointing practice.