Case study: Figuring out the upgrade to hospital essential power systems

As part of a renovation project for a Boston-based health center, it was requested that its existing essential power system be upgraded due to the age and condition of the two generators located on the roof of the building. One of the generators served two automatic transfer switches (ATSs), one that fed an emergency panelboard originally designed for egress lighting and one that fed a standby power panelboard designed for receptacle and heating, ventilation and air conditioning (HVAC) loads. The second generator was dedicated to a separate standby power ATS to serve additional HVAC loads.

Over time, the loads served by each of these panels became mixed to the point where it was difficult to determine which panels were supposed to be dedicated to emergency loads.

To ensure the correct essential power system design was provided for the facility, several meetings were held between the owner and design team to determine the types of patient care that would be provided within the building and what flexibility would be needed in the future. Through these conversations and follow-up emails, it was determined that the facility would have no Category 1 spaces but would have Category 2, 3 and 4 spaces. However, there was a desire to keep the facility flexible should any Category 1 spaces be needed in the future.

Figure 4: Separation of essential electrical system branches, required for systems more than 150 kVA. Courtesy: Fitzemeyer & Tocci Associates Inc.

Based on these criteria from the owner, along with the budget constraints of the project, it was determined that a Type 2 essential power system was the correct solution for the project. Both generators on the roof were to be replaced and upsized based on the new load requirements of the renovation but instead of serving specific ATSs they were to be paralleled and connected to a new essential power switchboard. The decision to parallel the generators allowed engineers to bypass the requirement to add a temporary generator connection (NFPA 70: National Electrical Code (NEC) Article 700.3(F)) as each generator was sized appropriately to carry the life safety loads of the building should one of the generators need to be serviced.

The new essential power switchboard was designed with five sections:

• Two incoming generator breaker sections.

• One life safety branch section.

• One equipment branch section.

• One spare section.

Each section was designed to be vertically isolated from the other sections allowing the spare section to be used to feed a new critical branch if required by the facility if they add any Category 1 spaces in the future. This provided the flexibility desired by the owner while minimizing unnecessary costs for the project.

The existing emergency power ATS was replaced and tied into the new life safety section of the essential power switchboard. The existing standby transfer switches were replaced with one larger equipment branch ATS and a distribution panelboard to back feed each of the standby panelboards throughout the building from the new equipment branch section.

The branch circuit discrepancies were not addressed as part of this project but will be corrected in future renovation projects at the facility to ensure essential power loads are served from the correct branch based on the NEC requirements of Article 517.

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