Site Issue: Main Power Returned, but Some Racks or Cooling Circuits Did Not
A common site report is: “The generator started and the main switchboard is energized, but one rack row, a PDU or part of the cooling system is still down.” The cause is often circuit zoning, transfer logic, maintenance bypass or labeling records.
ATS/STS and low-voltage distribution are not accessories; they are critical nodes in the backup chain. Unclear labels, unidentified single points of failure or missing test records reduce overall availability.
Configuration Review: Single-Line Diagram and Transfer Equipment Data
Place utility, UPS, generators, ATS/STS, PDUs, racks and cooling circuits on one power-path diagram to identify single points, misconnections, overloads and circuits that cannot be bypassed for maintenance.
- Distribution single-line diagram, ATS/STS specifications, PDU and rack count, and circuit schedule.
- A/B feeds, critical-circuit redundancy, maintenance bypass and breaker selection.
- Recent transfer and load tests, circuit labels and inspection records.
- Rack-density changes, expansion plans and cooling-load connection methods.
Why This Design: the Transfer Path Must Be Testable, Isolatable and Maintainable
Data center transfer equipment must support testing, maintenance and fault isolation—not only automatic transfer. A system without bypass or clear labels can create a new outage during maintenance.
Review breaker interrupting capacity, cable ratings, grounding, circuit redundancy, PDU allocation and expansion allowance. In existing facilities, engineers also verify that drawings match the field installation.
Review Documents: Single-Line Diagram and Circuit Schedule
- Single-line diagram for utility, UPS, generators, ATS/STS, PDUs and rack distribution.
- ATS/STS specifications and breaker, cable, grounding and maintenance-bypass data.
- PDU and rack count, A/B feeds and critical-circuit schedule.
- Transfer tests, load tests, inspection sheets, fault records and expansion plans.
- Whether on-site circuit verification, label correction and long-term monitoring reports are required.