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Thread: hospitals - Life Safety vs Critical

  1. #1
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    hospitals - Life Safety vs Critical

    Reviewing a set of drawings for a hospital that has two isolated breakers at the emergency generator. One goes to an Equipment ATS (450A) and the other goes to a DP. The DP then feeds a Critical ATS and a Life Safety ATS.

    In reviewing 517.30 it strikes me that this is taking a liberty with the code. If the system is less than 150KVA you could go to a single ATS, but I don't see anywhere where they permit the arrangement so described above. What do you think?

    Also when 517 talks about systems smaller than 150kVA, are they talking about the Life safety and Critical systems combined? Or is this inclusive of the equipment load as well?

    Thanks,

    Mike
    Mike Shields, PE
    Boston, MA

  2. #2
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    Quote Originally Posted by mshields
    Reviewing a set of drawings for a hospital that has two isolated breakers at the emergency generator. One goes to an Equipment ATS (450A) and the other goes to a DP. The DP then feeds a Critical ATS and a Life Safety ATS.

    In reviewing 517.30 it strikes me that this is taking a liberty with the code. If the system is less than 150KVA you could go to a single ATS, but I don't see anywhere where they permit the arrangement so described above. What do you think?

    Also when 517 talks about systems smaller than 150kVA, are they talking about the Life safety and Critical systems combined? Or is this inclusive of the equipment load as well?

    Thanks,

    Mike
    Mike,

    This is the commentary in the NECHB that goes with 517.30.


    FPN Figure 517.30, No. 1 and FPN Figure 517.30, No. 2 illustrate possible electrical system connections for hospitals. For a small electrical system having a maximum demand on the essential electrical system of 150 kVA, see FPN Figure 517.30, No. 2. A small load can be served by a single transfer switch that can handle the loads associated with both the emergency system and the equipment system. This, of course, is based on the assumption that the transfer switch has sufficient capacity to handle the combined loads and that the alternate source of power is sufficiently large to withstand the impact of the simultaneous transfer of both systems in the event of a normal power loss. For further explanation of loads permitted on an emergency system, see NFPA 99-2005, Standard for Health Care Facilities, 4.4.2.2.
    The requirement in 517.30(B)(6) correlates with 12.3.3.2 of NFPA 99.

  3. #3
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    517.30 is a page and a half long, so I'm not sure exactly what part you don't think this meets. But I think you will find certain AHJ's would allow this, and others wont.

    Regarding the single transfer switch, the 150 KVA limit if for all three - life safety, critical, and equipment - combined.

    Steve

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