Circuit Breaker Maintenance Flashcards
6 cards from real NETA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Circuit Breaker Maintenance flashcards as text
Vacuum circuit breakers extinguish arcs by:
Answer: Relying on the high dielectric strength of vacuum to prevent re-ignition after current zero
In vacuum interrupters, arcing occurs in a vacuum envelope. At the first natural current zero, the arc cannot sustain due to the absence of ionized particles, and the high dielectric recovery of vacuum prevents re-ignition.
What is the purpose of the anti-pumping feature in a circuit breaker control circuit?
Answer: To prevent multiple close-open cycles when close command is held while the breaker trips
Anti-pumping prevents the breaker from rapidly cycling between closed and open if the close control signal remains active while an automatic trip occurs. This prevents mechanical damage.
When performing contact wear measurement on a vacuum circuit breaker, the technician is measuring:
Answer: The contact erosion or stroke reduction from arcing
Contact wear in vacuum circuit breakers is measured as the reduction in contact stroke (erosion indicator). As contacts erode from arc interruption, the contact gap when open decreases, eventually reaching the end-of-life limit.
A circuit breaker's interrupting rating is different from its continuous current rating because:
Answer: Interrupting rating is the maximum fault current the breaker can safely clear, while continuous rating is the maximum normal load current it can carry
Continuous current rating (amperes) is the normal load current. Interrupting rating (kA symmetrical) is the maximum short-circuit fault current the breaker can safely interrupt without damage.
The purpose of a slow close test on a circuit breaker is to:
Answer: Manually operate the mechanism to observe contact alignment and travel
A slow close test manually moves the breaker mechanism slowly through its closing operation, allowing visual inspection of contact alignment, contact touch, wipe, and full close position without electrical testing.
What should be verified when testing the trip coil of a circuit breaker?
Answer: Coil resistance, minimum voltage to operate, and that it releases the trip latch reliably
Trip coil testing should verify DC resistance (for continuity and coil integrity), minimum operating voltage (to ensure reliable tripping even with degraded battery voltage), and functional latching release.