Upgrading a chiller plant can be one of the most exciting projects for an engineer to work on, specifically when the plant needs to be kept fully operational during the construction process. Figure 1 shows the layout of a typical chilled water plant that is near the end of its useful life. Figures 2 and 3 show the piping system diagram: The plant is comprised of three water-cooled chillers, each sized for approximately 30% of the load, and arranged in a primary-secondary configuration. Three equally sized constant-speed and constant-flow towers are used to cool the condenser water. As shown in Figure 1, a motor control center (MCC) is used to deliver and control power to the central plant equipment and other ancillary loads. It is not unusual for older central plants to be provided with an MCC; one of the main reasons for this approach was the lack of variable frequency drives (VFDs) to control motor loads. An MCC is comprised of multiple “buckets,” with each bucket representing an assembly of a circuit breaker, motor starter, and a means to disconnect power to a load.