Guides
Power reaches a data-centre IT load through a chain: utility and generator, transfer switching, the UPS, then distribution down to the rack. The architecture decides how many of those links can fail or be maintained without the load noticing.
Eaton's UPS basics paper describes three redundant arrangements:
| Architecture | How it works | What a failure does |
|---|---|---|
| Zone | One or more UPS dedicated to a set of resources | The impact is limited to that zone |
| Serial | UPS connected end to end | If one fails, the others compensate automatically |
| Parallel | Independent UPS feeding a common output bus, synchronised to share the load | Any one UPS can fail or be isolated while the others carry the load |
It also notes that a centralised design uses larger UPS than a distributed one. Dual delivery paths, as in Tier III and IV sites, go further: two complete paths, each able to carry the load.
Both work; they place risk differently. A centralised design puts large UPS in one plant room and distributes protected power across the building; Eaton notes that it uses larger kVA UPS than a distributed scheme, where smaller UPS sit closer to the loads they protect. Centralised plant is easier to maintain and monitor in one place; distributed systems limit how much load one failure can reach, much as the zone arrangement does.
Because a second path does nothing for a device with one power cord. Uptime Institute notes that Tier III sites use dual power paths for concurrent maintainability, that Tier IV adds autonomous response to failures, and that single-corded devices turn up in more installations than they should. Large static transfer switches upstream are one way owners try to give single-corded loads two sources; Uptime describes rack-mounted or point-of-use transfer switches as the way to keep that risk as low as possible.
More than a simple load. Cummins lists the data-centre loads a generator must carry: UPS rectifiers that create harmonics, capacitive filters and IT power supplies with a leading power factor, and constant-power loads. It warns that low kW with high leading kVAR is a risk for the alternator, and suggests a generator mode on the UPS where available. Eaton's generator guidance adds that the generator must hold voltage and frequency inside the UPS's input window, or the UPS stays on battery. More in UPS and generator compatibility.
The architecture sets the ceiling; operations decide how close the site gets to it. Uptime Institute's point applies here: long-term value depends on how a site is operated. For maintenance of the UPS layer across Canada, see UPS service for data centres.
Two complete power paths, each able to carry the full load, so either can fail or be maintained. Redundancy counting is explained in the N+1 and 2N guide.
Yes, to protect the server itself. A single-corded device on a dual-path site depends on one path, unless a point-of-use transfer switch feeds it.
Between the utility-generator transfer and the distribution to the racks, carrying the load through the generator start and conditioning the supply.
Because a generator that cannot hold the UPS's input window leaves the UPS on battery, and some UPS input characteristics are hard on alternators.
Sources, checked 2026-10-04:
Tell us the site, the UPS and the timing. We reply and quote within 4 business hours, or call 1 (438) 800-0382
Brand names are trademarks of their owners and are used only to identify the equipment we service. We are not the manufacturer and are not affiliated with it.