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Thread: Generator Load Bank Testing

  1. #1
    Join Date
    Aug 2010
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    Generator Load Bank Testing

    When performing the annual load bank test on a generator as required by NFPA 110, I wanted to know the following.

    1. Can the normal power to the building be maintained operational while the load bank test takes place?
    2. If so, can the ATS be set to stay in the normal position and not transfer to the to emergency position during the test? How is this done?
    3. In my case, I am designing a generator project that will have one load breaker and one breaker for connecting the load bank mounted on the generator. Do I have to interlock these breakers to make sure that when the load bank breaker is in the on position, the load breaker is in the off position? Code requirement?

  2. #2
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    Aug 2010
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    One more thing, this generator serves only an optional stand-by branch. No Emergency stand-by or Legally Required stand-by, as defined by NEC 701 & 702.

  3. #3
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    Quote Originally Posted by Shujinko View Post
    One more thing, this generator serves only an optional stand-by branch. No Emergency stand-by or Legally Required stand-by, as defined by NEC 701 & 702.
    Is this still required to have an annual test? We shut off all load breakers and connect only the load bank when testing. The load bank is sized based on the parameters of the test.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    Quote Originally Posted by infinity View Post
    Is this still required to have an annual test? We shut off all load breakers and connect only the load bank when testing. The load bank is sized based on the parameters of the test.
    Annual load bank testing is required by NFPA 110, Section 8.4.2 if your loads on the generator during monthly testing don't meet the minimum exhaust gas temperatures as recommended by the manufacturer or don't reach 30% of the KW on the gen-set nameplate.

  5. #5
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    Quote Originally Posted by Shujinko View Post
    One more thing, this generator serves only an optional stand-by branch. No Emergency stand-by or Legally Required stand-by, as defined by NEC 701 & 702.
    If that's the case, then NFPA 110 does not even apply. You are free to test it any way you see fit, or not at all.
    If this was for an Article 700 system then you would have to comply with 110. That would include having means available automatically to power the emergency system even while testing or load banking. Also, under the 2017 NEC there is a new requirement in 700.3(F) related to this. In recent years all sorts of specialized gear has become available for this. Some applications even go so far as to install permeant load banks with fully automatic switching.

  6. #6
    Join Date
    Nov 2017
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    Ventura County, Ca
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    Hi Shujinko,
    To answer your questions directly, presuming this is a commercial system.
    1. The ATS will not transfer to emergency as long as utility is present.
    2. Your gen breaker will be open so it can't switch anyway.
    3. Having a load bank breaker makes connection of the load bank quite simple. Your gen techs will love you! The breakers have no requirement to be interlocked, code or other. As this is a manual operation care must be taken when testing to configure the breakers as required especially when completing your testing, to leave the building load breaker closed, the LB breaker open and the genset in auto! Hope this helps!

    BTW, I'm a long time reader and registered to help here.

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