Separately Derived Systems

Q. Dan, Are hospital generators always considered separately derived systems?

A. Hospitals are not always considered separately derived.

If the generators are operating at 208V with 3-pole transfer switches, or are 480V generators with main circuit breakers less than 1000A in size, then being separately derived is not a requirement. If you have 4-pole transfer switches with any voltage, you need to have the generator be separately derived.

It really is a voltage and size issue dictated by the NEC for all applications, not just hospitals.

Christopher L. Mouer, E.I.
Principal, Project Manager
TLC Engineering for Architecture
255 South Orange Avenue, Suite 1600
Orlando, Florida 32801-3463
(w) 407.841.9050
(f) 407.540.0234