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Reference
Tiers & scale, at a glance.
Two tables worth bookmarking: the Uptime Tier levels that define resilience, and how requirements shift across small, medium and large builds.
Uptime Institute
Tier I to Tier IV.
| Attribute | Tier I | Tier II | Tier III | Tier IV |
|---|---|---|---|---|
| Redundancy | N | N+1 | N+1 | 2N / 2N+1 |
| Distribution paths | 1 | 1 | 2 (1 active) | 2 (both active) |
| Concurrently maintainable | No | No | Yes | Yes |
| Fault tolerant | No | No | No | Yes |
| Availability (approx.) | 99.671% | 99.741% | 99.982% | 99.995% |
| Two utility feeds required? | No | No | No | No* |
*Common in practice for cost and safety, but not a Tier requirement — generators are the recognised primary source.
By scale
Small, medium and large.
| By scale | Small | Medium | Large / Hyperscale |
|---|---|---|---|
| Typical use | Server room, edge, SME | Enterprise / colo floor | Colo campus, cloud, AI |
| Racks | 1–10 | 10–100 | 100 – several thousand |
| IT load | 5–50 kW | 50 kW – 1 MW | 1 MW – 100+ MW |
| Redundancy | N / N+1 | N+1 | 2N / 2N+1 |
| Cooling | Precision / split AC | CRAC + containment | Chilled water + liquid |
| Power | UPS + small DG | UPS bank + DG | MV distribution, DG plant |
Not sure which tier or scale fits you?
The right answer depends on what downtime costs your business. We help you decide before you commit.
Talk to SNA Power