Circuit Breaker Maintenance Flashcards
7 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 7 Circuit Breaker Maintenance flashcards as text
According to NETA MTS, what is the recommended maximum contact resistance for a 15 kV vacuum circuit breaker measured across each pole?
Answer: 100 microhms
NETA MTS specifies that contact resistance for medium-voltage vacuum circuit breakers should not exceed 100 microhms per pole unless the manufacturer specifies otherwise.
Which dielectric test method is used to verify the vacuum integrity of a vacuum interrupter bottle?
Answer: DC hi-pot test across open contacts
A DC hi-pot test applied across the open contacts of a vacuum interrupter checks the vacuum integrity; a degraded vacuum will allow current to flow at lower voltages than expected.
When performing a trip timing test on a low-voltage power circuit breaker, what parameter is being verified?
Answer: Time from trip signal initiation to contact separation
Trip timing tests measure the elapsed time from when the trip signal is applied to when the main contacts physically separate, verifying the breaker responds within manufacturer specifications.
A power circuit breaker's charging spring fails to charge after the close-open operation. The MOST likely cause is:
Answer: Failed spring charging motor or limit switch
The spring charging motor or its associated limit switch is the most common cause of failure to recharge the closing spring after an operation.
NETA recommends that circuit breaker insulation resistance tests be performed at what minimum test voltage for 600 V class breakers?
Answer: 500 V DC
For 600 V class equipment, NETA MTS recommends a 500 V DC megohmmeter test voltage to measure insulation resistance.
Which condition does the 'wipe' measurement on a circuit breaker describe?
Answer: The travel distance of the contacts after initial touch during closing
Contact wipe (also called overtravel) is the distance the moving contact continues to travel after it first makes contact with the stationary contact, ensuring proper contact pressure.
During a circuit breaker maintenance inspection, you find carbon tracking on the arc chute. The CORRECT action is to:
Answer: Replace the arc chute assembly
Carbon tracking on arc chutes creates a conductive path that can cause flashover; arc chutes with carbon tracking should be replaced, not cleaned and returned to service.