What Is Emergency vs. Standby Power?
Emergency power systems (NEC Article 700) serve life-safety loads — egress lighting, fire alarms, elevators for firefighter use — and must restore power within 10 seconds with the highest reliability requirements. Standby systems (NEC Articles 701/702) serve everything else the owner wants powered during outages — HVAC, data centers, production — with 60-second restoration and flexible design. The classification determines the generator, transfer switch, wiring, and testing requirements.
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Emergency systems (Article 700)
Legally required for life safety: the loads the code mandates (egress illumination, exit signs, fire alarm, emergency communications). Requirements: automatic transfer within 10 seconds, dedicated wiring separated from all other systems, monthly testing under load, and fuel for the code-required duration. Emergency systems get the most stringent installation rules because lives depend on them directly.
Legally required standby (701) vs. optional standby (702)
Article 701 covers systems the code requires for non-life-safety reasons (hospital equipment branches, smoke control, critical infrastructure) — 60-second restoration, still legally mandated. Article 702 is optional standby: whatever the owner chooses to back up (data centers, commercial kitchens, home generators) — the owner's design, the owner's reliability target. Most commercial generators serve 701/702 loads; the emergency system is the smaller, stricter subset.
Design considerations
The electrical engineer separates the three systems (700/701/702) with independent transfer switches and distribution — mixing them violates the code. Generator sizing considers the largest motor starting, harmonic loads (UPS systems), and selective coordination of the overcurrent protection. Fuel: diesel (with fuel-polishing maintenance for stored fuel), natural gas (no storage limits, utility-dependent), or propane. Monthly load-bank testing keeps the system reliable — untested generators fail when needed.
The bottom line
Emergency (700) = life safety, 10-second restoration, strictest rules. Standby (701/702) = everything else, 60 seconds. Separate the systems, size for motor starting, and test monthly.
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