buying guide

Reading an Insulator Datasheet Before You Order

Which figure to design against, which one is a type test result, and which dimensions decide whether the unit fits your structure.

Failing Load Is Not Working Load

A glass disc quoted at 210 kN is stating its mechanical failing load, the destructive type test result. The figure to design against is the routine proof value applied to every unit, 105 kN in that case. On ANSI porcelain discs the equivalent pair is combined M&E strength, 67 kN on a 52-3, against a 33.3 kN routine proof test load and maximum working load.

Creepage, Spacing and Shed Diameter

Creepage per unit drives the unit count for your pollution class. Spacing drives total string length and therefore the tower window check. Shed diameter drives the swing envelope and, in substations, enclosure clearance. All three are published per type, and all three have to pass.

Dry and Wet Withstand Figures

Dry and wet power-frequency withstand voltages are quoted separately because the wet value is measured under standard artificial rain, which shorts part of the leakage path. For exposed line work the wet figure is the conservative reference. Impulse withstand and, on some designs, polarity-dependent critical impulse flashover values are given alongside.