This part of IEC 383 applies to insulator strings and insulator sets comprising string insulator units of ceramic material . or glass for use on a.c. overhead power lines with a nominal voltage greater than 1 000 V and a frequency not greater than 100 Hz. This part of IEC 383 also applies to insulator strings and insulator sets for use on d.c. overhead electric traction lines. This part of IEC 383 also applies to insulator strings and insulator sets of similar design when used in substations. It may be regarded as a provisional standard for insulator strings and insulator sets for use on d.c. overhead power lines and for composite insulator sets. The object of this part of IEC 383 is to prescribe standard electrical test procedures and acceptance criteria to verify the defined characteristics of insulator strings and insulator sets falling within the scope of the part of IEC 383. These tests and characteristics are intended to give a common base to designers, users and suppliers of overhead lines, insulators and line equipment when definition, evaluation or verification of the electrical characteristics of such equipment is required. These tests are not intended to be mandatory tests on insulators whether supplied individually or as strings or as sets. NOTES 1 Tests on string insulator units are dealt with in IEC 383-1. Tests on composite insulators are dealt with in IEC 1109. 2 This part does not include artificial pollution or radio-interference tests. These subjects and relevant test methods are dealt with in the following IEC reports: IEC 437: Report — radio interference test on high-voltage insulators. IEC 507: Report — artificial pollution tests on high-voltage insulators to be used on a.c. systems. 3 Power arc tests are currently under study.