Last month, I covered the first part of the requirements for types and sources of power for life safety systems for hospitals. This article continues this discussion, because hospitals and the systems that power them are critically important. These power systems are the basis of healthcare facilities, and we must be able to rely on their continued operation and reliability. We should train electricians on the importance of these systems and compensate them appropriately for their expertise. 

Most hospitals use power from electric utilities and generators as on-site power sources to supply the life safety and critical branches. Both of these rely on the equipment branch for building operation. Let’s examine each branch’s importance in powering a hospital. 

Life safety branch

As you may remember from last month’s article, the life safety branch provides power to electrical equipment necessary for egress and exit lighting and alarm and evacuation systems. However, while most residential, commercial and industrial buildings use life safety systems to successfully evacuate a building and the emergency power must only last long enough to get people out of the building in an emergency, hospitals and similar facilities do not operate that same way. It is possible many critical patients cannot evacuate safely. They may need to be relocated or stay in the intensive care unit while the hospital’s critical power is maintained. During and immediately after Hurricane Katrina in 2005, all hospitals in the area lost both normal power from the electric utilities and emergency power for the life safety and critical branches, which is a situation that everyone wants to avoid in future natural disasters. 

Critical branch

The critical branch supplies power for all task illumination to ensure proper medication; adequate lighting for deep sedation, anesthesia and similar critical care; electrical equipment necessary for patient life support; and all essential power loads for proper patient treatment and care. 

New sources of power

Two new sources of power permitted in NEC 517.30 for the life safety and critical branches are energy storage systems covered in Article 706 and healthcare microgrids. Energy storage systems collect and store energy in battery systems from generators, utilities or renewable sources of energy, such as wind turbines and photovoltaic systems. 

These systems must have a capacity greater than 3.6 megajoules (greater than 1,000 watt-hours) of energy. They can be a standalone power source or interactive with other power sources in a microgrid. This stored energy system can be installed as a single separate building or multiple modular buildings used for emergency power for hospitals. These modular buildings are usually manufactured at a separate facility, shipped in and connected to the hospital quickly. 

A common power source is storing power from utility connections overnight to take advantage of low peak energy. 

Article 706 covers energy storage systems, and the overall scope is for the complete assembly for storing and exporting electrical energy from these modular buildings. NEC 706.2 requires these systems to be listed. NEC 706.4 requires the systems to have a visible nameplate after installation and be marked with the following: the manufacturer’s name, trademark or other descriptive marking by which the organization responsible for supplying the energy storage system can be identified; rated frequency; number of phases, if AC; rating in kilowatts or kilovolt-amperes; available fault current derived by the energy storage system at the output terminals; maximum output and input current of the energy storage system at the output terminals; maximum output and input voltage of the energy storage system at the output terminals; and whether the energy storage system can be utility-interactive. 

This last part is very important, since the energy storage system must be able to be disconnected from the utility if it loses power and is transferred using a transfer switch to directly connect into the hospital power source as part of the system’s essential electrical power microgrid. This isolates the utility grid during a power outage.

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