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Thread: 250.58 Clarification

  1. #1
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    250.58 Clarification

    250.58 Common Grounding Electrode. Where an ac sys-tem is connected to a grounding electrode in or at a build-ing or structure, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. Where separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding electrode(s), the same grounding electrode(s) shall be used. Two or more grounding electrodes that are bonded to-gether shall be considered as a single grounding electrode system in this sense.

    Does this mean that two services should be connected together only through one electrode, or can I use the last sentence to mean that I can connect one service to one electrode, have a bonding jumper to another electrode, and then connect the second service to that electrode?

  2. #2
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    Quote Originally Posted by George Stolz View Post
    or can I use the last sentence to mean that I can connect one service to one electrode, have a bonding jumper to another electrode, and then connect the second service to that electrode?
    I would say yes. In the code you quoted, I think "electrode(s)" and "electrode system" are being use to reference an electrode system as discussed in 250.50. Once you bond your two electrodes together, they become part of an electrode system. The two services can be connected to this system with a GEC connected to any of the electrodes in the system.

  3. #3
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    Common Grounding ac system

    Quote Originally Posted by George Stolz View Post
    250.58 Common Grounding Electrode. Where an ac sys-tem is connected to a grounding electrode in or at a build-ing or structure, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. Where separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding electrode(s), the same grounding electrode(s) shall be used. Two or more grounding electrodes that are bonded to-gether shall be considered as a single grounding electrode system in this sense.

    Does this mean that two services should be connected together only through one electrode, or can I use the last sentence to mean that I can connect one service to one electrode, have a bonding jumper to another electrode, and then connect the second service to that electrode?
    Hi George,

    The question you pose may have two directions of interpretation (in my mind) and affected by what code cycle of application. There are multifamily buildings that can have two separate ac sources to their respective Service Centers on the same structure. In days prior the UFER requirements, each Center had their own supplemental bonding.

    Present multi-family systems implementing a UFER foundation grounding electrode system are bonded together through a common (rebar) grounding system through the the foundation tied to both Service Center disconnects bonded with their respective GEC. (For all purposes...a Service Center with dual meters does not usually fall into this scenario.)

    I do not believe that the 250.58 intention of the "Two or more grounding electrodes" sentence "in this sense" being referred to in the supplemental arrangement would be applicable in the multi-family Separate Service Center applications I interprete. (if that is what is being asked.)

    Note: In multi-family structure, the separate Service Center serving one group of tenants are divided by a fire barrier from the other Service Center grouping.
    Last edited by gndrod; 01-05-12 at 04:49 PM. Reason: Added note.
    rbj, Seattle...Safety is a Professional Courtesy.

  4. #4
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    It is essentially saying each building or structure shall only use one set of grounding electrodes. Every electrode connected to one system must also be connected to all other systems. The GEC's are not required to be common, but a common GEC may be more cost effective in many instances.
    Last edited by Smart $; 01-05-12 at 04:46 PM.
    I'll never get there. No matter where I go, I'm always here.

  5. #5
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    Quote Originally Posted by George Stolz View Post
    or can I use the last sentence to mean that I can connect one service to one electrode, have a bonding jumper to another electrode, and then connect the second service to that electrode?
    This would be my interpretation but then since I think this is correct, it probably means the opposite...

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