Dirt contamination can reduce the interrupting capabilities by reducing the dielectric strength when moisture is present. Which statement best reflects this effect?

Dirt contamination can reduce the interrupting capabilities by reducing the dielectric strength when moisture is present. Which statement best reflects this effect?

• A. Increase dielectric strength
• B. Reduce dielectric strength
• C. Have no effect
• D. Improve arc quenching

Answer: (B)

Dirt contamination with moisture lowers the insulation’s ability to withstand voltage, called dielectric strength. When surfaces are dirty and damp, they form conductive paths and leakage currents, so the voltage needed to cause breakdown drops. With a lower dielectric strength, the ability of a breaker to interrupt a fault current is compromised because the arc can sustain more easily or flash over at lower voltages. So the correct description is that dielectric strength is reduced. Increasing dielectric strength would be the opposite of what actually happens, and claims of no effect or improved arc quenching don’t fit the degrade in insulation performance caused by dirt and moisture.

Dirt contamination with moisture lowers the insulation’s ability to withstand voltage, called dielectric strength. When surfaces are dirty and damp, they form conductive paths and leakage currents, so the voltage needed to cause breakdown drops. With a lower dielectric strength, the ability of a breaker to interrupt a fault current is compromised because the arc can sustain more easily or flash over at lower voltages. So the correct description is that dielectric strength is reduced. Increasing dielectric strength would be the opposite of what actually happens, and claims of no effect or improved arc quenching don’t fit the degrade in insulation performance caused by dirt and moisture.