This recommendation 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. The voltage bands defined are intended mainly for use in connection' with installation rules, but may also be used when preparing requirements for electrical equipment. Notes 1. — The extension of the scope to include frequencies higher than 60 Hz is under consideration. 2. — The voltage bands for d.c. installations are under consideration.