A 4.0 MW critical-load data center built to Uptime Institute Tier III — N+1 UPS topology, generator plant redundancy, and rack-level distribution, all organized around one question none of this program's other projects ask: how do you keep every component maintainable without ever touching the load?
The project brief: a single-building enterprise data center with a critical IT load of approximately 4.0 MW across roughly 650 server racks, 480V utility service from an on-site substation, an N+1 modular UPS plant feeding rack-level PDUs, and an N+1 diesel generator plant with automatic transfer. Tier III's technical definition — concurrently maintainable — means every capacity component and distribution path has to be removable for planned maintenance without ever interrupting the critical load, which reshapes UPS module count, generator count, and distribution topology in a way no other project in this program requires.
This module walks the whole project end to end: why critical IT load and mechanical/cooling load are deliberately kept on separate distribution paths, the N+1 UPS topology and a full worked sizing calculation showing exactly why five 1.0 MW modules (not four larger ones) makes the concurrent-maintainability math work, the generator plant's parallel N+1 design and closed-transition transfer scheme, and rack-level dual-corded distribution with static transfer switches for legacy single-corded loads. The full worked numbers and complete bill of materials are part of the unlocked module below.