Hospitals are obligated by law and building code to have backup generators with multiple (at least 3) separate backup power feeds for critical branch, life safety branch, and equipment branch. These are defined as ‘essential loads’ by the National Electrical Code. They can all be fed from the same generator but must use separate overcurrent protection and automatic transfer switches.

Critical branch is defined as loads that are used for direct patient care, plus ‘additional task lighting, receptacles, and circuits needed for effective hospital operation.’

Life safety branch is the fire alarm system and emergency lighting, plus elevator lights and controls, medgas alarms, PA/notification systems used during building evacuation, and some generator accessories.

Equipment branch has some require items including OR cooling, patient room heating, and data rooms. Some hospitals will add MRIs, non-patient care HVAC, and chillers (for air conditioning) on the generator backup system as well.

There’s typically a fourth system for everything else (‘normal’ power) that is not backed by a generator. Non-emergency lighting, convenience receptacles, and other non-essential loads are on this system.