Applies to d.c. and three-phase a.c. machines, with shaft heights 56 mm and higher and a rated power up to 50 MW, at nominal speeds from 600 rev/min up to and including 3 600 rev/min. For vertical machines, applies to those machines which are measured in a state of free suspension, and excludes those exceeding a shaft height of 400 mm. The contents of the corrigendum of August 1984 have been included in this copy.