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Thread: 120/208 3w vs 4w?

  1. #1
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    120/208 3w vs 4w?

    Hi i am understanding a 120/208 3 Phase service needs to have 3 conductors, one for each phase brought from the utility secondary. This service is a Wye formation, so we need to bring the neutral from the utility transformer wye secondary as well. My question is do I need to bond my neutral and ground at the service panel if I am bringing a neutral from the utility? I am currently showing a 120/208 3 phase service that bonds the neutral and grounding electrode conductor at the panel. I thought I could "derive" my own neutral at the panel and not pull a neutral from the utility. Would this be a 3 wire panel then?

    Can I show a 3 wire panel and derive my own neutral at the panel and not pull a neutral from the utility? ( I have single phase 120V loads)

    Should I show a 4 wire panel and pull a neutral from the utility? Do I need to show a bonding jumper at my panel in this case?

    Thank you, just trying to get this confirmed.

  2. #2
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    Quote Originally Posted by Honeycone View Post

    Can I show a 3 wire panel and derive my own neutral at the panel and not pull a neutral from the utility? ( I have single phase 120V loads).
    Just for my sake, how would derive a neutral at the panel?

    Should I show a 4 wire panel and pull a neutral from the utility? Do I need to show a bonding jumper at my panel in this case?
    Yes to both.
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #3
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    Quote Originally Posted by jumper View Post
    Just for my sake, how would derive a neutral at the panel?
    And don't say "by connecting to ground"!

  4. #4
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    Quote Originally Posted by GoldDigger View Post
    And don't say "by connecting to ground"!
    Darn it Goldy, you blew my trap!!!!

    I wanted to see if he fell for it.
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #5
    Join Date
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    Quote Originally Posted by Honeycone View Post
    Hi i am understanding a 120/208 3 Phase service needs to have 3 conductors, one for each phase brought from the utility secondary. This service is a Wye formation, so we need to bring the neutral from the utility transformer wye secondary as well. My question is do I need to bond my neutral and ground at the service panel if I am bringing a neutral from the utility? I am currently showing a 120/208 3 phase service that bonds the neutral and grounding electrode conductor at the panel. I thought I could "derive" my own neutral at the panel and not pull a neutral from the utility. Would this be a 3 wire panel then?

    Can I show a 3 wire panel and derive my own neutral at the panel and not pull a neutral from the utility? ( I have single phase 120V loads)

    Should I show a 4 wire panel and pull a neutral from the utility? Do I need to show a bonding jumper at my panel in this case?

    Thank you, just trying to get this confirmed.
    Really, Ground Fault Currents are trying to get back to its source NOT ground. In your case the source is the utility transformer.
    A ground fault travels through your EGC, through your main bonding jumper, and then through your utility neutral back to it's source.
    Yes, absolutely, you need to bond your neutral to your grounding bus..it's called the "Main Bonding Jumper", otherwise, your ground fault condition may not find it's way back to it's source. Then the excessive current to trip a C/B will then not be available, leaving a dangerous scenario.
    Your Main bonding Jumper completes a circuit back to the transformer allowing the excessive current to trip a C/B.
    Your utility neutral not only carries the unbalance current back to the XFMR, but it is also used for ground fault currents.

  6. #6
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    250.24(C) Grounded Conductor Brought to Service Equipment.
    Where an ac system operating at 1000 volts or less is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through 250.24(C)(4).
    Don, Illinois
    The code only applies to T&M work....it does not apply to contract work.

  7. #7
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    Disregarding what happens during a fault for the moment - you still need the neutral conductor back to the source for proper operation of 120 volt loads.

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