scope:

This standard is applicable to string insulator units of the long rod type with insulating parts of ceramic material intended for a.c. overhead lines with a nominal voltage greater than 1000 V and a frequency not greater than 100 Hz. The smallest insulator unit standardized has a lightning impulse withstand voltage of 125 kV. It is also applicable to insulators of similar design, used in sub-stations. This standard is applicable to string insulator units of the long rod type either with a clevis at both ends for coupling with a tongue, or with a socket at both ends for coupling with a pin ball. This standard is applicable to string insulator units with external metal fittings.