This Mission Critical Data Center required additional backup power capacity to support current and future missions, with no allowance for termination of services. This included replacing the high maintenance rotary UPS System (3-1.8MW units) which had proven unacceptable time and expense to keep the system at 100% capability. A new main-tie-main medium voltage distribution/control system was provided with generator backup (N+1). Both the utility and generator medium voltage switchgear was designed to all full maintenance without equipment shutdown. Redundant generator controls were also provided to avoid a single point of failure. The new UPS system was designed as modular distributed (2N) redundant (3 MW). The initial UPS capacity will be 2 MW upgradable to 3 MW without any system outages. The new computer room air conditioners and humidifiers are designed to be 2N redundant with dual-path chilled water piping. The upgrade doubles the electrical capacity and all construction will be phased to avoid impacting facility operations.