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Thread: I have a ground rod question. Installing a new 120/240v service. Going to install 2 g

  1. #21
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    Quote Originally Posted by Adamjamma View Post
    A single rod could be good enough if it has a low enough resistance... I forget how the code reads but there is a level there that if you read under that, you’d not need a second ground rod. The second rod is to try to get the Ze under the amount needed sofaults will trip the breakers. It is all about Ze and Ze... and breaker trip current amounts.
    You're misunderstanding what Infinity and myself are getting at. He has been around for a while, I'm sure he knows when two rods are required and when they are not.

    If the service requires a grounding electrode system and takes two rods to get it done, why would an outbuilding requiring a grounding electrode system only need one?

    Second, I believe you're mistaken on rods playing a part in the operation of breakers sensing overcurrent conditions.

  2. #22
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    Quote Originally Posted by Cow View Post
    1)You're misunderstanding what Infinity and myself are getting at. He has been around for a while, I'm sure he knows when two rods are required and when they are not.

    2)If the service requires a grounding electrode system and takes two rods to get it done, why would an outbuilding requiring a grounding electrode system only need one?

    3)Second, I believe you're mistaken on rods playing a part in the operation of breakers sensing overcurrent conditions.
    1) I believe that I do.
    2) That was exactly my point.
    3) Yes, grounding electrodes play no part in opening the OCPD's. That is the function of the EGC and the MBJ.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  3. #23
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    Quote Originally Posted by Adamjamma View Post
    A single rod could be good enough if it has a low enough resistance... I forget how the code reads but there is a level there that if you read under that, you’d not need a second ground rod. The second rod is to try to get the Ze under the amount needed sofaults will trip the breakers. It is all about Ze and Ze... and breaker trip current amounts.
    Not only do you forget how the code reads you forget the most basic of all concepts about grounding and bonding, that the earth is never to be relied on to clear a fault.
    If you don't think too good, don't think too much.

  4. #24
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    Quote Originally Posted by Cow View Post
    You're misunderstanding what Infinity and myself are getting at. He has been around for a while, I'm sure he knows when two rods are required and when they are not.
    I have been, and I thought so. Apparently, I'm wrong in this case.

    If the service requires a grounding electrode system and takes two rods to get it done, why would an outbuilding requiring a grounding electrode system only need one?
    Because a service and a sub-panel have different requirements, so I've always thought.

    That's what I was taught, I've always done, and always passed inspection with only one.

    Second, I believe you're mistaken on rods playing a part in the operation of breakers sensing overcurrent conditions.
    Definitely agree; electrodes are not required to have low-enough impedance to trip OCPD's.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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