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Exams > 2023 Q47 — 125VDC Mechanical Interlock and Bus Transfer

2023 Q47 — 125VDC Mechanical Interlock and Bus Transfer

⚠️ DRAFT
Q47 — 125VDC Mechanical Interlock and Bus Transfer T2G1 063 K4.01 (3.4)
Which of the following completes both statements concerning the 125 VDC Electrical Distribution System?

1. The 125 VDC Distribution System design (1) include a mechanical interlock when transferring from normal to the backup (emergency) bus.
2. Transferring 125 VDC distribution loads to the backup bus is permitted during (2).
A. (1) does NOT (2) ALL Modes
B. (1) does NOT (2) Modes 5, 6, or defueled Only
C. (1) does (2) ALL Modes
D. (1) does (2) Modes 5, 6, or defueled Only
▶ Show Answer & Explanation
✓ D. Correct. The 125 VDC system does include a design feature that prevents paralleling the normal and backup busses. A mechanical interlock located in the distribution panel requires the normal supply breaker to be open and then the mechanical device is allowed to move allowing the closing of the backup or emergency power. Per procedure, transferring to the backup DC bus is only allowed during Modes 5, 6, or defueled.
✗ A. Incorrect. Part 1 is incorrect. Plausible because the operator may incorrectly recall that the DC busses do not have a mechanical interlock. Incorrect in that a mechanical interlock is part of the design. Part 2 is incorrect. Plausible because the operator may misinterpret the questions and believe that the DC bus can be transferred during any modes. Incorrect in that paralleling DC bus will make the DC busses Inoperable during Modes 1-4.
✗ B. Incorrect. Part 1 is incorrect. Plausible because the operator may incorrectly recall that the DC busses do not have a mechanical interlock. Incorrect in that a mechanical interlock is part of the design. Part 2 is correct.
✗ C. Incorrect. Part 1 is correct. Part 2 is incorrect. Plausible because the operator may misinterpret the questions and believe that the DC bus can be transferred during any modes. Incorrect in that paralleling DC bus will make the DC busses Inoperable during Modes 1-4.
Ref: NOS05DCELECT-11 | Source: Bank — Salem | Cognitive: Fundamental/Memory
K/A: 063 K4.01 — Knowledge of DC Electrical Distribution System design features and/or interlocks that provide for the following: Manual/automatic transfers of control.

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