Refer to the simplified drawing of an electrical distribution system showing 7.2 KV switchgear, step-down transformers, and 480 V motor control centers (MCCs) (see figure below).
The high voltage side of each step-down transformer has a remote-operated disconnect.
The control circuit for each disconnect is position-interlocked with the associated MCC feeder breaker.
Which one of the following describes the interlock operating scheme that will provide the greatest protection for the disconnect?
A. Permits opening the feeder breaker only if the disconnect is closed.
B. Permits opening the feeder breaker only if the disconnect is open.
C. Permits opening the disconnect only if the feeder breaker is closed.
D. Permits opening the disconnect only if the feeder breaker is open.
Show Answer
Answer: D
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