Q46 — 125VDC Ground Detection
T2G1 063 K1.01 (2.6)
Given:
• Salem Unit 2 was at 100% power
• During control room log taking, the operator observes the 2A 125 VDC Bus ground ohmmeter reading 40K Ω (ohms)
Based on the above condition, which of the following completes both statements?
1. The reading indicates that a ground on the bus (1) detected.
2. If a ground is detected, S2.OP-SO.125-0004, 125VDC Ground Detection, will (2).
• Salem Unit 2 was at 100% power
• During control room log taking, the operator observes the 2A 125 VDC Bus ground ohmmeter reading 40K Ω (ohms)
Based on the above condition, which of the following completes both statements?
1. The reading indicates that a ground on the bus (1) detected.
2. If a ground is detected, S2.OP-SO.125-0004, 125VDC Ground Detection, will (2).
A. (1) is NOT (2) open all breakers in the panel, then reclose them one at a time, if no change to ground readings then continue
B. (1) is NOT (2) open one breaker at a time, evaluate ground readings, leave open if ground clears
C. (1) is (2) open one breaker at a time, evaluate ground readings, leave open if ground clears
D. (1) is (2) open all breakers in the panel, then reclose them one at a time, if no change to ground readings then continue
▶ Show Answer & Explanation
✓ C. Correct. Per S2.OP-SO.125-0004, a resistance reading of 50K ohms or less indicates a ground is detected. A resistance of greater than 50K ohms is normal indicating no grounds are present. Therefore, a ground reading of 0 ohms indicates a hard ground is present. Per S2.OP-SO.125-0004, breakers on the bus will be opened one at a time until the resistance indicates greater than 50K ohms.
✗ A. Incorrect. First part is incorrect. Plausible because the operator can incorrectly recall and confuse which resistance reading indicates a ground present and believe that the 0 ohms indicates no grounds. Incorrect in that resistance reading less than 50K ohms is a ground. Second part is incorrect. Plausible again if the operator confuses how to interpret resistance readings and believes a lower resistance is good.
✗ B. Incorrect. First part is incorrect. Plausible because the operator can incorrectly recall and confuse which resistance reading indicates a ground present and believe that the 0 ohms indicates no grounds. Incorrect in that resistance reading less than 50K ohms is a ground. Second part is correct.
✗ D. Incorrect. First part is correct. Second part is incorrect. Plausible because the operator can incorrectly recall and confuse which resistance reading indicates a ground present and believe that the 0 ohms indicates no grounds. Incorrect in that resistance reading less than 50K ohms is a ground.
Ref: NOS05DCELECT-11 | Source: New | Cognitive: Fundamental/Memory
K/A: 063 K1.01 — Knowledge of the physical connections and/or cause and effect relationships between the DC Electrical Distribution System and the following systems: Ground detection system.
K/A: 063 K1.01 — Knowledge of the physical connections and/or cause and effect relationships between the DC Electrical Distribution System and the following systems: Ground detection system.
Connections
- Related systems: DC Power
- Related procedures: S2.OP-SO.125-0004 — 125VDC Ground Detection
- Related exam: 2023 NRC Written Exam