NETA Circuit Breaker Maintenance 3

Question 1

Vacuum circuit breakers extinguish arcs by:

Accepted Answer

Relying on the high dielectric strength of vacuum to prevent re-ignition after current zero

Answer

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.

Question 2

What is the purpose of the anti-pumping feature in a circuit breaker control circuit?

Accepted Answer

To prevent multiple close-open cycles when close command is held while the breaker trips

Answer

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.

Question 3

When performing contact wear measurement on a vacuum circuit breaker, the technician is measuring:

Accepted Answer

The contact erosion or stroke reduction from arcing

Answer

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.

Question 4

A circuit breaker's interrupting rating is different from its continuous current rating because:

Accepted 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

Answer

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.

Question 5

The purpose of a slow close test on a circuit breaker is to:

Accepted Answer

Manually operate the mechanism to observe contact alignment and travel

Answer

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.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Circuit Breaker Maintenance 3