Forums » Electrical Engineering

Bonding jumper

    • 19 posts
    January 13, 2019 9:13 AM PST

    Does the 12.5% rule apply when sizing a bonding jumper for a metal water piping system?

    • 200 posts
    January 13, 2019 11:04 AM PST

    If you are using NFPA/NEC (USA code) in some cases "12.5% rule" applies, in some cases DOESN'T. But but I confess to being afraid to give a complete answer, because the Z4E has been totally reset recently. So far my entire contribution has been lost, just like the previous Z4I site. Let's wait for the site to stabilize so we can respond better.

     


    This post was edited by Alex de Moura at January 13, 2019 11:17 AM PST
    • 19 posts
    January 13, 2019 11:15 AM PST

    OK thank you.

    • 140 posts
    January 16, 2019 1:23 PM PST

    A you meaning grounding electrode conductor to a water pipe?  That's 250.66 however a bonding jumper is based on table 250.102(C)(1)

     

    Note 1 of T 250.102 states-- other notes may apply depending on your situation

     

    If the ungrounded supply conductors are larger than 1100 kcmil
    copper or 1750 kcmil aluminum, the grounded conductor or bonding
    jumper shall have an area not less than 121∕2 percent of the area of the
    largest ungrounded supply conductor or equivalent area for parallel
    supply conductors. The grounded conductor or bonding jumper shall
    not be required to be larger than the largest ungrounded conductor or
    set of ungrounded conductors.

    • 19 posts
    January 16, 2019 1:34 PM PST

    • 140 posts
    January 16, 2019 2:16 PM PST

    So the bonding jumper to the transformer as shown above, would be based on T. 250.102(C)(1).  However a bonding jumper to a water pipe would not need to be larger than the grounding electrode conductor that it is jumped from.  Maybe I am misunderstanding the question because you mentioned water pipe but the diagram does not have a water pipe.