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Thread: Seperately derived system

  1. #11
    Join Date
    Jul 2003
    New Jersey
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    Quote Originally Posted by Hoggedy View Post
    So, I was told to look at 250.92 services. where it states that normally non current carrying metal parts shall be bonded together.
    So I think the issue here is dictating whether or not this is considered a service or a separately derived system.
    The conductors feeding the disconnect are going to be fed from a cable that will then be connected to a Meltric on the side of a breaker panel. The breaker (branch circuit) will feed the cable, in turn feeding the switch(primary side of transformer) and then the secondary side will feed another panel.
    wouldn't a service only be the wires between the serving utility and the service equipment? making the service only the points where it enters our company? everything downstream of that is feeders and branch circuits? in turn, a branch circuit feeds our switch to transformer, making that a separately derived system. Which would make it not necessary to bond the raceways?
    How do I distinguish what is a service and what is a SDS bonding raceways changes based on which one we are dealing with.
    An SDS has similar requirements regarding GEC's and bonding jumpers but it is not the same as a service. As Dave stated the definitions and distinctions between the two start in Article 100.

    For the record I still have guys telling me (incorrectly) that you need bonding bushings on a transformer because you "treat it like a service".


    All responses based on the 2014 NEC unless otherwise noted

  2. #12
    Join Date
    Mar 2005
    Hampton, VA
    0 Post(s)
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    The definition of service has always confounded a lot of people when it comes to industrial complexes where the service point is typically at a main substation and all the supplies to the buildings are then feeders and separately derived systems. As was mention earlier, there grounding requirements for services and other supplies are similar but not exactly the same. I have a few documents that I developed for my site to help our workers understand the differences. One shows the changes to the definition of services over the last 10 or so code cycles, one illustrates what constitutes a service, and one is a comparison of the code requirements for services to those for feeders and SDS's. They are too big to share as attachments but I am happy to share via email if you PM me your email address. It might help in discussions with your peers.

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