Know the electrical, power components in a data center

Overview

This article is a broad primer that walks through the power chain of a data centre from start to finish. It begins with the classification of emergency and standby loads under the NEC, then covers PDUs, UPS types, battery chemistries, DRUPS, containerized UPS and generators. The author, Murali Vakacharla, published it in Consulting-Specifying Engineer in 2026.

The most notable part of the article is a table (Table 1) showing typical UPS and generator redundancy and fuel autonomy by facility type: enterprise, colocation, hyperscale, edge, modular and telecom. Typical fuel autonomy is 2-4 h for enterprise, 24-72 h for colocation and hyperscale, 48-72 h for telecom, and minutes to 1 h for edge. The table is a practical benchmark for choosing a starting assumption for a facility type.

The article gives practical sizing rules for battery runtime, generator loading and fuel storage. For battery runtime, about 5 minutes is a practical baseline, Tier III/IV facilities need at least 15 minutes, and poorly maintained batteries are blamed for about 25% of dropped loads. Generators should be loaded to at least 30% to avoid wet stacking, and start time ranges from a few seconds to 30+ seconds per NFPA 110.

On fuel, mission-critical sites need 48-72 h; Level 1 EPSS in seismic design categories C-F may need 96 h, and each generator typically has a day tank of about 24 h. A typical critical block is about 2 MW IT plus 1 MW cooling, roughly 3 MW, usually with a dedicated generator. In the glossary, an ATS transfers in 50-200 ms plus 5-10 s of generator stabilization, and an STS in under 4 ms. These are practical values from the article and are not binding standards.

Key points

1. Typical fuel autonomy: enterprise 2-4 h; colocation and hyperscale 24-72 h; telecom 48-72 h; edge minutes to 1 h.
2. About 5 minutes of battery runtime is a practical baseline; Tier III/IV facilities need at least 15 minutes.
3. Poorly maintained batteries are blamed for about 25% of dropped loads.
4. Generators should be loaded to at least 30% to avoid wet stacking.
5. Generator start time ranges from a few seconds to 30+ s per NFPA 110.
6. Mission-critical sites need 48-72 h of fuel; Level 1 EPSS in seismic design categories C-F may need 96 h; each generator typically has a ~24 h day tank.
7. Typical critical block: about 2 MW IT plus 1 MW cooling = ~3 MW, usually with a dedicated generator.
8. ATS transfer 50-200 ms (3-12 cycles at 60 Hz per UL 1008) plus 5-10 s generator stabilization; STS transfers in under 4 ms.

Using it in design

• Seed facility-type templates with default UPS/generator redundancy and fuel autonomy from Table 1.
• Warn if battery autonomy is under 5 minutes (or under 15 minutes for Tier III/IV targets).
• Warn if generator minimum load is under 30%, and if fuel autonomy is under 48 h for mission-critical designs.
• Catalogue transfer devices (ATS, STS) with transfer-time fields.

Who should read it

Engineers new to the data centre power chain and designers setting UPS and generator assumptions by facility type.

Related standards

• NFPA 70 Art. 700/708
• NFPA 110
• NFPA 111
• TIA-942-C
• UL 1008
• UL 1778
• UL 2085

Publication details

Authors

Murali Vakacharla

Publisher

Consulting-Specifying Engineer

Year

2026

Document language

English

Source type

Expert / community

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation