Severe contamination of a dielectric medium can cause circuit breakers to __________ by allowing an arc to be sustained between the open contacts or the contacts and the grounded tank.

• A. Trip
• B. Explode
• C. Weld
• D. Short circuit

Answer: (B)

Contamination of the insulating medium lowers its dielectric strength, so an arc can form and be sustained even after the contacts separate or when a contact is near the grounded tank. That sustained arc dumps a lot of energy into the insulation and surrounding oil or gas, vaporizing it and rapidly increasing internal pressure. The sudden pressure rise inside the breaker can cause it to rupture or vent violently, i.e., explode. Tripping is a protective action that may occur later due to fault current, welding would involve the contacts sticking together, and a short circuit describes the electrical fault itself rather than the explosive event caused by an arc in a contaminated dielectric.