Applies to a.c. electrical installations of buildings supplied at a frequency not exceeding 60 Hz and at a nominal voltage up to and including 1 000 V. Defines two voltage bands: Band I covers the installations where protection against shock is provided under certain conditions by the value of voltage and the installations where the voltage is limited for operational reasons (e.g. telecommunications, signalling, bell, control and alarm installation). Band II contains the voltage for supplies to household, commercial and industrial installations. This band contains all the voltage of public distribution systems in the various countries. Note: The voltage bands defined are intended mainly for use in connection with installation rules (see IEC 60364), but may also be used when preparing requirements for electrical equipment.