A rack contains 20 1U servers with dual power supplies and two PDUs on separate 15A circuits. Each server is connected to both PDUs, and each server draws 1A of current in normal operation. One of…

Dual power supplies provide per-server redundancy against a single PSU failure, but cannot prevent the second circuit breaker from tripping when the total transferred load of 20A exceeds its 15A rated capacity.

Servers do not gracefully shut down in this scenario - the second circuit breaker trips instantly due to overload, resulting in immediate ungraceful power loss rather than a controlled shutdown sequence.

With 20 servers each drawing 1A, total load is 20A spread across two 15A circuits (approximately 10A each under normal operation). When one breaker trips due to a power surge, all 20A of load attempts to draw from the single remaining 15A circuit. This immediately exceeds the 15A breaker rating, tripping the second breaker and removing power from all servers simultaneously.

Half the servers losing power would only occur if each server had a single PSU connected to only one PDU; since every server has dual PSUs connected to both PDUs, the entire 20A load shifts to the surviving circuit and overloads it.