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Thread: Respective Branches for Legally Required and Optional Standby Loads

  1. #1
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    Respective Branches for Legally Required and Optional Standby Loads

    Hello All, I am new to this so be nice!!

    Here's my question, I understand that legally required and optional standby systems can have the same transfer switch, and even be fed from the same cabinet or switchboard section.. But since they are defined as different systems, do the respective branches eventually have to be separated at all?

    Example, A single ATS feeds a distribution panel, that panel has main breakers for legally required and optional standby systems, once the panel branches are the legally required and optional standby systems required to remain separate? Can you mix in the branch circuit loads with one another after the separation occurs? The reason I ask is I am running into an issue in the field with this, and the engineer is telling me its perfectly fine.. Why separate the systems at all?

    I cannot find anything to dispute this, but it seems like an uncommon practice, and do not think its a good one!

    I hope to learn a lot from this forum, and some of your Great Minds!!!

  2. #2
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    The engineer is fudging or at least stretching the wording. Read 700.10(B) taking special note of (5) and then 701.10 taking note of "general wiring" it does not mention "emergency wiring".

    Look at page 49 of this link for examples.

    Roger
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  3. #3
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    Unless the facility falls under 517.
    The more they overthink the plumbing, the easier it is to stop up the drain

  4. #4
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    Quote Originally Posted by dkidd View Post
    Unless the facility falls under 517.
    Even then you can pretty much look at the Life Safety Branch in alignment with 700 (see 517.26), the Critical Branch as 701 (except you can not install in raceways or enclosures with "general wiring"), and the Equipment Branch as 702.

    Roger
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  5. #5
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    Quote Originally Posted by Sam@CEgeeks View Post
    I understand that legally required and optional standby systems can have the same transfer switch, and even be fed from the same cabinet or switchboard section..
    Only in a health care facility with a total demand on the essential system is less than 150KVA.

    Otherwise, you need separate transfer switches.

  6. #6
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    Quote Originally Posted by steve66 View Post
    Only in a health care facility with a total demand on the essential system is less than 150KVA.

    Otherwise, you need separate transfer switches.
    Thank you for the response, could you give me some more information regarding this? So if it’s not a health care facility with a total demand on the essential, separate transfer switches are needed? This is an Assembly Occupancy, considered a high rise under the Florida Building Code.. any input is greatly appreciated

  7. #7
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    700.6 D - Transfer equipment shall only supply emergency loads.

    That is assuming you have a true emergency system, and you don't have battery powered exit lights and emergency lights.

    Also, if its a high rise, you should also read through article 700. It has some additional requirements for a high rises and/or assembly occupancies.

  8. #8
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    Quote Originally Posted by steve66 View Post
    700.6 D - Transfer equipment shall only supply emergency loads.

    That is assuming you have a true emergency system, and you don't have battery powered exit lights and emergency lights.

    Also, if its a high rise, you should also read through article 700. It has some additional requirements for a high rises and/or assembly occupancies.
    his wording implies that he is referring to article 701 systems not 700 systems


    I know what I don't know, and I know where to go to find it!

  9. #9
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    Quote Originally Posted by Sam@CEgeeks View Post
    Hello All, I am new to this so be nice!!

    Here's my question, I understand that legally required and optional standby systems can have the same transfer switch, and even be fed from the same cabinet or switchboard section.. But since they are defined as different systems, do the respective branches eventually have to be separated at all?

    Example, A single ATS feeds a distribution panel, that panel has main breakers for legally required and optional standby systems, once the panel branches are the legally required and optional standby systems required to remain separate? Can you mix in the branch circuit loads with one another after the separation occurs? The reason I ask is I am running into an issue in the field with this, and the engineer is telling me its perfectly fine.. Why separate the systems at all?

    I cannot find anything to dispute this, but it seems like an uncommon practice, and do not think its a good one!

    I hope to learn a lot from this forum, and some of your Great Minds!!!
    I am not familiar with a code that allows (or prohibits) a single ATS and panel to act as both NEC 701 and 702 systems. If it exists I assume it would be in NFPA 110. That said, 701.10 clearly allows both system to share the same everything. No ambivalence.


    I know what I don't know, and I know where to go to find it!

  10. #10
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    Quote Originally Posted by Strathead View Post
    I am not familiar with a code that allows (or prohibits) a single ATS and panel to act as both NEC 701 and 702 systems. If it exists I assume it would be in NFPA 110. That said, 701.10 clearly allows both system to share the same everything. No ambivalence.
    Yes, your are right - he did say legally required. And if that is the case, then I agree with your answer.

    But it really makes me scratch my head because to the best of my knowledge, I have never ran across a "legally required system".

    So now I'm wondering if I have been mis-classifying systems. I know I have asked the difference between what systems are emergency and what are legally required, but I'm not sure I ever got an answer that was definitive.

    Almost all buildings require egress lighting and exit lighting with a second source of power. I have always assumed those lights and exit signs are "Emergency Systems". The IBC even uses the phrase "emergency power".

    So are exit lights and dual head egress lights emergency, or legally required?

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