What Is Inrush Current?_
Inrush current occurs when capacitive or inductive components in power supplies, such as input capacitors or transformers, initially charge or magnetize. This surge can be many times the steady-state operating current and may last from milliseconds to seconds. It must be accounted for in circuit breaker sizing and power distribution design to avoid nuisance tripping.
Technical Details
Inrush current magnitude depends on the power supply topology, input voltage phase at turn-on, and the impedance of the upstream circuit. Active inrush limiting circuits (e.g., NTC thermistors or relay-bypassed resistors) are commonly used to reduce peak current. In GPU racks, multiple power supplies energizing simultaneously can compound inrush, requiring staggered power-up sequences or soft-start modules per the OEM’s installation guide. The relevant electrical code and facility power study should verify that branch circuit breakers and PDUs can handle the combined inrush without tripping.
How Leviathan Systems Works with Inrush Current
During initial rack power-up, Leviathan field crews sequence PDU breakers and GPU server power supplies to prevent cumulative inrush from tripping upstream protection. We also verify that any active inrush limiting in the liquid cooling distribution units (CDUs) is functioning per the manufacturer’s startup procedure.
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