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Thread: NEC 2008 Article / section 702.5 (B)2

  1. #1

    NEC 2008 Article / section 702.5 (B)2

    This topic has been covered before but it still is not clear to me what the code panel means here. My inquiry to all the 2008 NEC knowledgeable folks out there is based on this recent emailed article I received from NEC Plus. The quote from the article:

    Question:
    Does Section 702.5(B)(1) of the 2008 NEC require a manual standby system to be sized according to the total calculated load of the occupancy?

    Answer:
    Section 702.5(B)(1) in the 2008 NEC requires that optional standby systems with manual transfer equipment only have "adequate capacity and rating for the supply of all equipment intended to be operated at one time." It is not necessary to have capacity for all the connected load. Section 702.5(B)(1) states that "the user of the optional standby system shall be permitted to select the load connected to the system" and this load selection can be performed through manual shedding of the load that is not intended to be operated at one time. The user of the system can, during the period of utility power outage, perform connection and disconnection of various loads based on their needs. This is different from 702.5(B)(2) which requires capacity for full load, or the load determined by an automatic load management system.

    In NY we are moving to the 2008 NEC in January 2011. Yes we are always behind.
    As I understand the change to 702.5 from the 2005 NEC if auto bus transfer equipment is used per 702.5(B)2 the generator must be sized for the connected load or load management equipment must be introduced. In this case the " full load" /connected load is that which is determined by Article 220.
    My question is, if the electrician is choosing the calculation method are the calculations based upon the calculated connected load the client wants on the generator or the calculated connected load on the service?

    Due to snow and wind storm (and picturesque trees and no rights of way to trim them) we have many many residential generator installations in this part of the country (Where NY borders MA/VT/CT). Due to labor cost most if not all residences have 200 ampere services instead of the 100 -150 they really need based upon the Article 220 calculated load for designing the service size. If the 2008 NEC's new requirement is for the service calculated connected load, I envision minimum 25 KVA generators (at least not 50KVA based on the service size).

    If that is the case I suspect load management equipment will be the choice in the future ........ or manual transfer..

    Comments on what the Code actually means here?

  2. #2
    Join Date
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    I believe that you have it correct.

    If you are using an automatic transfer switch then the generator must be capable of suppling the full load that is transfered by the automatic transfer equipment or have a load management system that sheds the loads to that of the capacity of the generator.

    Chris

  3. #3
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    I agree you have a good handle on it.
    My question is, if the electrician is choosing the calculation method are the calculations based upon the calculated connected load the client wants on the generator or the calculated connected load on the service?
    The load would be what is calculated for the service if using a ATS. One way to over come it is to install a sub panel with only critical loads which would let you go with a smaller kw gen. set if the customer felt they could live with out a few things.
    Organized people are people that are just too lazy to look for their stuff

  4. #4
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    Quote Originally Posted by ceb58 View Post
    I agree you have a good handle on it.


    The load would be what is calculated for the service if using a ATS. One way to over come it is to install a sub panel with only critical loads which would let you go with a smaller kw gen. set if the customer felt they could live with out a few things.
    How can you say that they are in between two different requirements?
    Are/ What are they meeting 2005 or 2008, or the requirement is to meet in 2011 reflective of 2008?

    2008 is 100% last of my understanding!
    Last edited by cadpoint; 07-13-10 at 10:12 PM.
    = : )

  5. #5
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    Fine I missed it! The target is shreaded...
    = : )

  6. #6
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    Quote Originally Posted by cadpoint View Post
    Fine I missed it! The target is shreaded...
    Jude, take 2 asprin and call Dennis in the morning
    Organized people are people that are just too lazy to look for their stuff

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