CompTIA Server+ (SK0-005)TroubleshootingHard
A server rack is experiencing intermittent power loss to several devices. The power distribution unit (PDU) connected to these devices is rated for 20A, and the circuit breaker for the rack is also 20A. A technician calculates the total continuous load of all connected devices to be 18A. However, several devices have peak power draw ratings that, if combined, could momentarily exceed 20A. Which of the following is the MOST likely cause of the intermittent power loss?
- AFaulty PDU.
- BCircuit breaker tripping due to transient overload.
- CLoose power cables to the devices.
- DInsufficient cooling in the rack.
Show answer & explanationAnswer & explanation
Correct answer: B. Circuit breaker tripping due to transient overload.
Circuit breakers are designed to trip when the current exceeds their rating. While the continuous load is 18A (within 80% of 20A, which is 16A, and also 100% of 20A), momentary peak power draws from multiple devices simultaneously can cause the total current to spike above 20A, leading to the breaker tripping. This is a common issue with servers that have dynamic power consumption.
Why the other options are wrong
- A. While possible, a faulty PDU would likely cause more consistent or random failures, not specifically tied to load spikes.
- C. Loose power cables would cause power loss to individual devices, not intermittent power loss to several devices from the PDU/breaker level.
- D. Insufficient cooling leads to device shutdowns or performance throttling, not direct intermittent power loss from the PDU/breaker.
Circuit Breaker Overload
Circuit breakers protect electrical circuits by tripping and cutting power when the current exceeds a safe limit, often due to a sustained or transient overload from connected devices.
- Rated for maximum current flow.
- Trip when current exceeds rating, even momentarily.
- Continuous loads should ideally not exceed 80% of breaker capacity to prevent nuisance trips.
Memory trick: If the power keeps cutting, the breaker's likely strutting its stuff too much.