Your questions answered: Critical power: hospital electrical systems

The Sept. 15, 2016, “Critical Power: Backup power systems” webcast presenters addressed questions not covered during the live event.

By Danna Jensen, PE, LEED AP BD+C, and Robert R. Jones Jr., PE, LEED AP September 21, 2016

Designing hospital electrical systems is more demanding than for conventional commercial buildings because the stakes are so high. When specifying electrical distribution systems in hospitals, engineers must account for the facility’s size, flexibility needs, medical equipment and procedure types, essential (emergency) power needs, and safety requirements. They must design and coordinate electrical protection for all branches and the equipment fed by them. In addition, they must consider whether to apply isolated power systems.

The Sept. 15, 2016, “Critical Power: Backup power systems” webcast presenters addressed questions not covered during the live event. The presenters are:

  • Danna Jensen, PE, LEED AP BD+C, vice president, ccrd, a WSP | Parsons Brinckerhoff Co., Dallas
  • Robert R. Jones Jr., PE, LEED AP, JBA Consulting Engineers, Las Vegas

Q: Describe some typical issues that the local authority having jurisdiction (AHJ) wants corrected.

Danna Jensen: The inspectors tend to look for things that are regularly missed, or new additions to the code. A list that I’ve assembled that are typically on the top of the list for items written up during an inspection include:

  • Battery lights in anesthetizing locations
  • Battery light, life-safety light, and receptacle at automatic transfer switch (ATS) and generator locations
  • Bond between the normal and critical panelboards in electrical rooms
  • Patient care area receptacle testing (resistance, contact tension, and millivolt leakage).

Q: Can renewable energy sources be integrated with the essential electrical system?

Robert R. Jones Jr.: Possibly, but it may be cost-prohibitive. Renewable energy sources are not specifically listed as an acceptable source of power in NFPA 70: National Electrical Code (NEC) Article 517, but battery systems are. A renewable energy source could be used to charge the batteries. However, the demand and consumption requirements of a hospital would likely require a very large battery system. Batteries currently require a lot of physical space and are expensive to maintain.

Q: Are there any additional considerations when using a natural gas genset versus a diesel genset for backup power?

Jensen: There are two main considerations for using natural gas versus diesel. First, does your local authority consider natural gas as meeting the requirement for onsite storage of fuel (this is a requirement in NFPA 110: Standard for Emergency and Standby Power Systems and the number of hours depends on your facility classification, but typically not less than 24 hours). I have not found many jurisdictions that do.

Second, is the natural gas generator capable of being up and running and all loads connected to it within 10 seconds? This is a requirement of NFPA 110 for Level 1 systems (which a hospital is classified as). Natural gas engines start slower than diesel and, depending on the size of the engine, may have trouble getting to the required ratings within 10 seconds.

Q: Can mobile backup generators not on the premise still be deployed and used to power a hospital during an emergency?

Jones: NEC Article 517 requires that a generator be located on the premises and sized to support the essential electrical system (EES) demand. Nothing precludes the installation of provisions to hook up a mobile generator in addition. Applications may include backup of the permanently installed generator due to failure/maintenance or supply of nonessential loads desired to maintain normal operations during an extended loss of utility.

Q: What is a good demand factor you would suggest to use in addition to the NEC demand factors to keep generators sized well?

Jensen: The demand factors must be used per NEC. There are specific demand factors that can be used for lighting and receptacles in a hospital (NFPA 70-T220.42), elevators (NFPA 70-T620.14), diagnostic equipment (NFPA 70-517.73(A)(2), and so on. You must collect historical data to use the demand calculations listed in NFPA 70-517.30(D). This can be done by compiling a database as shown in the presentation, or by metering the load on the transfer switches and using that data.

Q: Which branch should a nurse call system be connected to, life safety or critical?

Jones: Nurse call systems should be connected to the critical branch. Refer to NEC Article 517.33(A)(5).

Q: What about pharmacies? Do those fall under NFPA 99: Health Care Facilities Code?

Jensen: It depends on their license. Most are designed to fall under USP 797 (or the newer version 800), however if they are not licensed under the hospital, they are not required to follow NFPA 99. If not, they can even be classified as “B” occupancy since there is not inpatient care provided.

Q: You indicated that 36 outlets are required in new operating rooms. Does that mean 36 double-outlet receptacles?

Jones: The receptacles provided to satisfy NEC Article 517.19(C) may be any combination of single, duplex, or both.

Q: NEC Article 700 requires surge protection device (SPD) protection of all distribution equipment. Does this apply only to the life safety branch? Are SPDs required for critical or equipment somewhere else in the code?

Jensen: Yes. The requirement for SPDs listed in NEC Article 700 applies only to the life safety branch because both NEC Article 517 and NFPA 99 state that the life safety branch of the EES shall meet the requirements of article 700 (NFPA 70-517.26 and NFPA 99- SPDs are not required for critical or equipment branches elsewhere in NFPA 99 or NFPA 70-517.

Q: Are special insulation requirements for isolated power conductors still required?

Jones: It would be a best practice to design the isolated power system with components to minimize leakage current from line to ground. NEC Article 517.160(A)(6) Fine Print Note 2, which is explanatory only and not actual code, suggests minimizing branch circuit conductor length and the use of conductors with insulation properties of less than a 3.5 dielectric constant and resistance greater than 20,000 meg-ohms at 60°F. Type XHHW conductors are suggested over the use of THHN/THWN.

Q: It is my understanding that the separation of emergency circuits begins at the transfer switch, not the upstream gear.

Jensen: The code does not distinguish one way or the other. However, it is inferred by the diagrams in the handbook and the wording in the text that the “branch” consists of all wiring and feeders, including the upstream overcurrent protective device (OCPD), which must be selectively coordinated. I also have run across many jurisdictions that consider the branch to start at the first OCPD supplying the transfer switch.

Q: Nursing home and long-term care facilities require only two branches, correct?

Jones: NEC Article 517.41(A) contains the requirements for the EES in nursing homes and limited care facilities. If the facility admits patients who may need to be sustained with life support equipment or performs surgical treatment requiring general anesthesia, an EES is required. The EES is comprised of the life safety branch and the critical branch.

Q: Are you allowed to shed the equipment branch to serve a fire pump?

Jensen: No. If your system is running as usual (meaning all designed engines are still operational), then all of the required systems must be connected and operational as well. This includes the automatically connected equipment branch. The only time load shed is permitted is if the load is optional to begin with, or you lose an engine or other catastrophe in which additional measures must be taken to keep as many systems operational as possible. Note however, when the fire pump is running and you have a fire in the facility, unless you have an intricate smoke control system, you will likely have a reduced load on the equipment branch b the air handling unit will de-energize upon sensing smoke in its return detector at the unit.