Hospitals' Emergency System Connections
I enjoy testing my NEC knowledge by reading your “Quizzes on the Code” column. I believe your answer to Question No. 1 of the Oct. ’98 issue, which states that emergency system transfer switches are only permitted to supply emergency loads, conflicts with Art. 517—Health Care Facilities. Sec. 517-30(b)(4) states that one transfer switch may serve one or more systems in a hospital with less than 150kVA in total essential system load, (which is illustrated in Fig. 517-30[C]). Thus, the hospital emergency system and equipment system could be supplied from a single transfer switch. The designer must make sure the transfer switch is sized to carry the combined systems load, and that the emergency power source can handle the transfer of both systems during a power outage.
Kurt Niven, P.E.
With respect to the first question of “Quizzes on the Code” (Oct. ’98 issue), I believe you may be a bit presumptuous to say a “surgical compressed air system” cannot be considered an emergency load in hospitals.
The emergency system includes a critical branch. Sec. 517-33(a)(9) of the 1996 NEC allows the user to determine what is needed for “effective hospital operation.” Thus, he or she can put that load on the critical branch. How can you take such a rigid position to the contrary? Are inspectors and electrical engineers now going to decide medical matters?
John K. Carter, P.E.
Let’s not forget that the answers in October’s “Quizzes” address articles in Ch. 7 of the Code. These answers call for the best response—not the perfect response. In regard to the small hospital system, Mr. Niven correctly points to a direct conflict in the 1996 NEC with respect to emergency system connections. Art. 700 (the quiz subject) says a single transfer switch is prohibited, and Art. 517 says it’s fine. Although Sec. 90-3 resolves seeming conflicts between the first four Code chapters and Chapter 5, 6, and 7, it doesn’t here because these latter chapters are equal rank. Conflicts between them have no simple resolution. I should have explained this in the response, but space is always tight in this department.
Mr. Carter is correct to write that if the hospital administration makes a conscious and properly documented decision to so classify the surgical compressed air system as one to be on the critical branch, the decision rests with them— not with an electrical official.
Sec. 517-34(a)(3) describes such systems as part of the equipment system. Furthermore, this material is extracted from NFPA 99, Health Care Facilities Standard. That means the NEC Committee didn’t even come up with the language. Instead, the hospital specialists comprising the NFPA 99 Committee developed the requirement.
This provision in the 1999 NEC has an additional sentence expressly stating these systems may be connected to the critical branch. If I run this question again in 2001, I’ll try to remember to pick a different load.