NEC 517.31(B) / NFPA 110 Type 10
What it means on the job
This fails code. NEC 517.31(B) requires the life safety branch to be restored within 10 seconds of power interruption. While the 5-second ATS delay is a common technique for avoiding unnecessary transfers during momentary utility fluctuations, the total 13-second restoration time (8-second generator start + 5-second ATS delay) exceeds the absolute 10-second maximum. The ATS time delay must be shortened or eliminated for the life safety branch to meet the code requirement. Critical life safety loads — exit signs, egress lighting, fire alarm — cannot be dark for 13 seconds during a hospital emergency. NFPA 110 classifies hospital generators as Type 10, meaning 10 seconds maximum from any cause of power loss to full restoration.
Tested in 1 CraftIQ puzzle
- code-checkEmergency Power Transfer Time
Related NEC sections
NEC 517.30(B)(1)
NEC 517.30(B)(1) requires transfer switches for the essential electrical system to be located in spaces that minimize the possibility of interruption from fire, flooding, or vandalism. An unsecured mechanical room exposes the transfer switch to damage or tampering, which could disable the entire essential electrical system during an emergency.
NEC 517.30(C)(1)
NEC 517.30(C)(1) ('Separation from Other Circuits') requires the life safety branch and critical branch wiring to be kept entirely independent of all other wiring and equipment — they cannot share the same raceway, box, or cabinet with normal power circuits. Mixing essential electrical system branch wiring with normal power circuits in the same conduit means a single conduit failure could disable both the essential and normal systems simultaneously, defeating the purpose of the essential electrical system.
NEC 517.30(G)
NEC 517.30(G) ('Coordination') requires overcurrent protective devices serving the essential electrical system to be coordinated for the period of time a fault's duration extends beyond 0.1 second. (This is coordination beyond 0.1 s, not the full selective coordination to time zero required elsewhere.) Without a coordination study, a fault on a single branch circuit could trip the upstream feeder breaker, causing a blackout across the essential electrical system — including life safety loads like exit lighting and fire alarm systems.
NEC 517.31(B) / NFPA 99 Section 6.4.1.1.4
NEC 517.31(B) and NFPA 99 Section 6.4.1.1.4 require the life safety branch of the essential electrical system to restore power within 10 seconds of utility failure. A 15-second transfer time means exit lighting, fire alarm systems, and critical corridor illumination remain dark for 5 seconds beyond the allowable limit — an eternity during a hospital evacuation.
NEC 517.33 / NEC 517.34
This fails code. NEC 517.33 and 517.34 specifically require nurse call systems, task illumination in patient care areas, and selected receptacles at patient bed locations to be connected to the critical branch of the essential electrical system. These loads are not optional — they must be on the critical branch regardless of generator capacity concerns. During a utility outage, patients on monitors and ventilators need powered receptacles, nurses need call system notification, and clinical staff need task lighting. If the generator cannot handle the full essential system load, the generator must be upgraded — not the load assignments reduced.
NEC 590.4(D) / high-rise office Specification
The high-rise commercial office specification requires all panels and breakers used for temporary lighting to be clearly labeled. Unlabeled temporary power creates confusion about which circuits are temporary vs. permanent and risks leaving construction power live during turnover.
CraftIQ explanations are original educational commentary written in trade language and verified against the cited standards. Always confirm requirements against the code edition adopted by your jurisdiction — this is training material, not a substitute for the code book or your AHJ.