This International Standard is applicable to string insulator units of the long rod type with insulating parts of ceramic material intended for use in a.c. overhead power lines with a nominal voltage greater than 1 000 V and a frequency not greater than 100 Hz. It is also applicable to insulators of similar design, used in substations. This standard is applicable to ceramic string insulator units of the long rod type, either with a clevis end fitting at both ends for coupling with a tongue, or with a socket end fitting at both ends for coupling with a pin ball. The object of this standard is to prescribe specified values for electrical and mechanical characteristics, and for the principal dimensions of ceramic string insulator units of the long rod type. This standard is applicable to string insulator units for use on overhead lines situated in lightly polluted areas, and the creepage distances given in table 1 have been established accordingly, using the IEC 60815 recommendation of 16 mm/kV for pollution level I. However, shorter creepage distances may be used in some non-polluted areas. If specific operating conditions require or allow non-standard (longer or shorter) creepage distances, the mechanical characteristics as well as the lengths L (see clause 4) of this standard should be used unless the need for exceptionally long creepage distances requires values of L greater than those given in table 1. In the case of special requirements, e.g. very heavy polluted areas and for other particular or extreme environmental conditions, it may be necessary for certain dimensions to be changed. NOTES 1 As far as reasonably applicable, this International Standard may also be applied to similar insulator units outside the scope of this standard, such as insulators for electric traction lines. 2 This International Standard does not include tests on insulators and dimensions of end fittings. 3 Ball and socket couplings are covered by IEC 60120, clevis and tongue couplings by IEC 60471. 4 For the definition of pollution levels, see IEC 60815. 5 The term "ceramic" is used in this International Standard to refer to porcelain materials and, contrary to North American practice, does not include glasses.