Case study: When an EPSS fails, what happens next?

Providing a hospital with temporary power was paramount.

By Richard Vedvik PE, CHEPP, Principal, IMEG, Rock Island, Illinois January 14, 2025
Courtesy: IMEG

An existing heating water pipe had a structural failure due to age. This pipe was located above a hard-lid (gypsum) ceiling in the main electrical room that serves the entire hospital building. This resulted in water ingress in the main electrical gear for an unknown amount of time until it was discovered in the hallway. The water filled several sections of switchgear, rendering the existing control logic unusable and rendering the generator main breaker and equipment branch transfer switch breakers as inoperable.

I got the call from the client and headed that way once I had gathered one-line diagrams for the entire facility. When I arrived and the draw-out 3,000 amp generator circuit breaker was removed from the gear with the generator locked out. This meant that the facility was without backup power.

The hospital had already transferred all critical patients to other facilities and was on bypass, a term used when emergency cases and ambulances are sent elsewhere. The facility was on utility power only and all transfer switches were in their normal position. Two large critical branch and equipment branch transfer switches were incapable of transitioning to emergency power. This is due to two factors: the lack of a functioning generator breaker and the failed control logic boards.

The existing main electrical service consists of a single lineup of switchgear with normal on one end, emergency on the other end and two large “transfer switches” in the middle. The two “transfer switches,” in between the normal and generator feeds, were electronically operated insulated case circuit breakers that are controlled by circa-1992 logic circuits and relays. Each transfer switch had two circuit breakers and the controls allowed for a closed transition or make-before-break operation.

  • One was rated for 1,600 amp and is the “normal power” source for the facility, meaning it serves loads that can be shed. The breakers in this gear were not damaged by water, but the logic controlling them was damaged. This breaker remained energized but was not able to automatically transfer until replacement parts arrived.
  • The other was rated for 1,000 amp and is the “critical branch power” source for the facility. These are loads that are required to be backed up for the facility to remain occupied. The circuit breaker in this gear was filled with water and no longer functioned.

Next, the team discussed what to do about the two operable breakers acting as transfer switches. The generator vendor suggested moving the emergency breaker in the critical transfer switch to the normal position in the equipment transfer switch. This would allow both to remain on normal power but would mean that neither transfer switch would have emergency power capability for the duration of the repair. The critical transfer switch loads are required to automatically transfer for the hospital to come off bypass.

My direction was to provide two functional circuit breakers in the critical branch switch and provide a temporary power source for the loads served by the equipment branch switch. This will allow the facility to come off the bypass as soon as the temporary feed is executed.

I then walked with the local electrical contractor to determine the best option for temporary power for the equipment branch loads. We discussed operating load and execution methods to ensure the solution could be installed in hours, not days or weeks. Our goal was to get the facility back online in a day or two. Temporary panels were chosen based on capacity and availability of existing spare circuit breakers. It was important to use existing circuit breakers to avoid delays. Of primary concern were elevators, which we wanted to remain on generator power.

After the plan was developed, we provided the hospital with a summary of our plans and the timeframe for temporary resolution. The generator vendor was also responsible for the breakers and controls in the switchgear lineup and they expect a 4- to 5-week timeframe to rebuild the circuit breakers and replace the control logic components. Interim controls were designed and implemented by the vendors and contractors.

The final component of the repair was what to do about the 3,000 amp generator breaker that had a long lead time. Luckily, the design team had recently replaced the 30-year-old standby generator with a new, exterior model and the new model had an onboard circuit breaker. This meant that the damaged circuit breaker was no longer necessary and busing could be installed where the breaker originally bolted in, which was able to be fabricated and installed on the same day.

Figure 6: Image of an existing emergency switchboard damaged by a leaking water pipe above. Courtesy: IMEG

Figure 6: Image of an existing emergency switchboard damaged by a leaking water pipe above. Courtesy: IMEG

The facility had also already experienced the coordination effort required for system shutdowns so they were able to duplicate that protocol. Due to the efforts by the team, the hospital was able to reoccupy and be fully operational just two and a half days after the initial outage. A second outage was scheduled five weeks later when the replacement breakers and controls were available and that installation process went smoothly.

This case study is just one example of how important emergency power supply system (EPSS) equipment location can be. While the existing main electrical room in this facility is not compliant with modern NFPA 110: Standard for Emergency and Standby Power Systems requirements in Chapter 7, for separation of normal service and EPSS in Level 1 systems, it was compliant when it was installed more than 30 years ago.

Many facilities are in similar conditions and designers should look at existing systems with a plan for improvements and upgrades, to prevent issues like this. While NFPA 70: National Electrical Code Article 110.26 prohibits foreign systems above electrical gear, a structural ceiling is allowed to be installed between the foreign systems and the electrical gear. However, the risks remain, as this situation indicates.


Author Bio: Richard Vedvik PE, CHEPP, is a senior electrical engineer and acoustic engineer with IMEG. He is a member of the Consulting-Specifying Engineer editorial advisory board.