Requirements for two types of board for electrical purposes made from glass bonded mica powder, from 1/8 in (3.2 mm) up to ½ in (12.7 mm) in thickness. Definitions, classifications, finish, flatness, thickness, electric strength proof test in oil, surface electric strength proof test in air, insulation resistance, carbon arc test, spirit burner test, water absorption, deformation under compression, shear strength and cross breaking strength. Methods of test given in appendices.Cross References:BS 46:Part 3BS 148BS 350BS 738 BS 871BS 2782:Part 4:Methods 430A to 430DBS 3497BS 3503BS 3591BS 3718IEC 167