Effective Utilization of Branches of Power in Hospitals

Hospitals are among the most challenging buildings to design, construct, and maintain. One of the most distinctive and code-heavy aspects of hospitals is that power supplied to the building must be split into separate “branches” of power. Sorting through applicable codes to determine what is allowed on each branch, however, can get tricky.

In typical non-healthcare facilities, an emergency generator supplies a life safety branch and also commonly an equipment branch. Hospitals and certain other healthcare facilities have an additional unique branch – the critical branch. Each branch is limited to allowing only certain types of loads and (unless meeting specific exceptions) must be fed via a dedicated automatic transfer switch. Codes also limit wiring methods for specific branches and call out maximum lengths of time for transfer to an emergency power supply.

Separation of branches allows for more crucial loads to remain powered and less crucial loads to be shed as the emergency generator becomes overloaded or is not able to generate power while meeting its rated output. These essential emergency systems requirements originate in NEC Article 517, NFPA 101, NFPA 99, and the FGI Guidelines for the Design and Construction of Healthcare Facilities.

The life safety emergency branch is dedicated to loads which serve to evacuate people out of the building safely, assist in first responder rescue operations, or provide the proper alarms for maintenance staff to resolve alarm conditions. The Life Safety branch is permitted to consist only of egress lighting, exit signs, alarms and alert systems (such as medical gas alarm panels and fire alarm equipment), emergency communications systems, generator accessories and power and lighting required for generator maintenance, elevator lighting and controls, and automatically operated doors.

The critical emergency branch is dedicated to patient care and life support. Requirements for this branch are very specific but allow some flexibility. The NEC identifies a number of specific critical loads, but also allows for “additional task illumination, receptacles, and selected power circuits needed for effective hospital operation.” Typically this branch powers emergency receptacles in patient rooms, patient room lighting, the nurse call system, medication fridges, and operational and patient health equipment. The flexibility allowed by the codes in this branch can even include items for patient comfort such as patient TVs or facility staff refrigerators, but due to generator sizing and transfer time requirements, adding these loads can become cost prohibitive. The extent of less crucial patient and staff comfort loads being placed on this branch is limited to the size, in amperage, supplied to the critical branch distribution equipment. Note however, that only single-phase fractional horsepower motors are allowed on this branch – anything larger must be connected to the equipment branch.

The equipment branch consists of mechanical equipment serving patient care areas and all other non-essential standby loads selected to receive emergency power. As large motors have the potential to shut down a branch or run down the generator quickly, they are forbidden on the life safety and critical branches. The equipment branch is permitted to be shed when the generator cannot produce its rated output, allowing the critical and life safety branches to remain online.

Navigating through the complex and changing codes governing healthcare emergency systems can be challenging. If you have questions on new emergency systems for healthcare facilities or are seeking to make compliant changes to an existing system, please contact Matt Bergey, EIT at mab@ba-inc.com or (717) 845-7654 for more information.