What Is Rack PDU Phase Rotation?_
Phase rotation refers to the order in which the three voltage waveforms (L1, L2, L3) are delivered to a three-phase PDU. Incorrect rotation can cause motors or certain power supplies to run backward or malfunction, though most modern IT equipment uses switched-mode supplies that are phase-agnostic. For data center racks, field crews confirm rotation matches the facility’s standard (typically clockwise or counterclockwise) using a phase rotation meter before connecting load cables.
Technical Details
Phase rotation is measured at the PDU input terminals using a rotation tester that indicates the sequence (e.g., ABC or ACB). In a 208/120 V or 480/277 V wye system, rotation must match the upstream panel schedule to avoid nuisance tripping of branch circuit breakers with electronic trip units. Some PDUs include built-in phase indicators, but field verification is still standard practice. The rotation is documented per rack and cross-checked against the site’s electrical single-line diagram.
How Leviathan Systems Works with Rack PDU Phase Rotation
During Leviathan Systems rack builds, the field crew checks phase rotation at every three-phase PDU before connecting any GPU server or networking gear. This step is part of the power pre-commissioning checklist, especially for high-density racks where multiple PDUs share a common feed.
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