AS IEC 60433-2007 pdf Insulators for overhead lines with a nominal voltage above 1000 V- Ceramic insulators for a.c. systems- Characteristics of insulator units of the long rod type

For the purposes of this International Standard, the following definition applies:
The corresponding values are specified in table 1. The minimum nominal creepage distances are based on a specific creepage distance of 16 mm/kV for the lowest value of the highest voltage for equipment corresponding to the specifed value of the standard lightning impulse withstand (in accordance with IEC 60071-1).
NOTES
1 The tolerances given in IEC 60383-1 are applicable to all the dimensions in table 1, even it the adjectives “minimum” or “maximum” are used before the term “nominal”.
2 Dry lightning impulse withstand vollage and wet power frequency withstand voltage are specifhed in table 1 for single unit string insulators. values of withstand voltages of insulator strings consisting of more than one unit are not contained in this standard.
3 The rod diameter is not specilied since it depends on the mechanical characteristics of the insulating material. Information on the definition and classification of ceramic insulating materials can be found in IEC 60672-1 and IEC 60672-3.
Long rod insulators are designated in table 1 by letter L, followed by a figure indicating the specified mechanical falling load in kilonewtons. Then follows the letters B or C indicating ball and socket or clevis and tongue coupling respectively, followed by the value of the lightning impulse withstand voltage in kilovolts.
The insulators shall be marked either on the upper shed or on the metal parts with the name or trade mark of the manufacturer and the year of manufacture. In addition, each unit shall be marked with the specified mechanical failing load, by using the first part of the designation; for instance, the insulator shall be marked L 160 for the units with 160 kN specified mechanical failing load.
These markings shall be legible and indelible.
Figure 1 shows a long rod insulator with clevis couplings, figure 2 shows a long rod insulator with socket couplings.