Which of the following is a common mechanical failure mode of insulators?

• A. Cracking from impact
• B. Electro-magnetic interference from nearby equipment
• C. Surface mottling due to UV only
• D. Color fading of glazing

Answer: (C)

Mechanical damage from external impact is a common failure mode for insulators. Porcelain and glass insulators are brittle, so a hard strike from hail, a dropped tool, or mishandling can create cracks. Once cracked, the insulator’s strength and its ability to isolate under voltage are compromised, increasing the risk of failure in service. By contrast, surface mottling or color fading caused by UV exposure describes aging or weathering of materials and is not a mechanical failure term. Electromagnetic interference from nearby equipment isn’t about the insulator’s physical integrity either.