The process for selecting the level of insulators made by composite or ceramic is identical. Based on strength alone, a composite insulator can directly replace insulators made of porcelain or glass.

Historically, when selecting a level of insulator a two to one safety factor has been applied because all materials have a time-load characteristic that reduces their residual strength over time. Most manufacturers rate composite insulators at a maximum working load equal to 50% of the ultimate Load rating.
Establishing the everyday working load of an insulator requires that ice and wind conditions for the area of application be considered. Ice and wind can add considerable load to the conductor and insulators, resulting in greater loads.

This calculation of the level of insulator does not include the weight of the insulators and other items that increase the load on the insulators. Normally, such items should be added to the final load. A composite insulator’s weight is a small percentage of the total weight; therefore, omitting it from the calculation will have minimal effect on the outcome.

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