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Thread: Distribution panel

  1. #1
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    Distribution panel

    I'm new here, thank you for the help in advance.

    I have a 600amp-480v panel, feed to a 25kva transformer, supply by a 30amp single phase breaker. Secondary side of transformer is feeding a 120/240v distribution panel(no main breaker at distribution panel) The equipment grounding conductor and the neutral conductor should be in the same bar or separate?
    if the can share the same bar, then do I need a main bonding jumper at the transformer?.

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    Welcome.

    There should be a neutral conductor and an EGC. They should be bonded at one point, either in the transformer or in the panel, but not both.

    In either case, it's good practice to wire the panel as if the neutrals and the EGCs are to be separate, even if the bond is to be in the panel.

    Don't forget your grounding electrode system.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    The bonding jumper at the transformer or the panel would be a system bonding jumper not a main bonding jumper. As Larry stated it needs to be either at the transformer or in the panel and at the same location that your GEC would connect. Also take a look at 408.36 regarding an OCPD for the panel.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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    Interesting on many fronts. I'm surprised your 25kva transformer doesn't trip due to inrush current.
    As to the transformer grounding/bonding the sketch below might help.
    As mentioned see 408.36 for requirement for a main.
    Click image for larger version. 

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ID:	22956
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    Very helpful

    I did look at 250.30(A)(1)(a)&(b) yesterday and the picture is just perfect. i can see now that both ways are correct as long as is not double bonded for it'll create parallel paths for ground and create a bigger hazard. And thank you for the correction on the main bonding jumper and the System Bonding Jumper, i saw that in the definitions. As far as the OCPD for the distribution panel it does not have one buacuse it falls into the 240.21(C)(1)(2) rule, but if i'm wrong please let me know.

    Thank you guys for taking the time to write back to teach others like me I will forward the knowledge and teach others.

    P.S my name is jay from Oklahoma working in the oilfield at the moment. PM me if you have more questions.

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    Quote Originally Posted by jctj88 View Post
    . . . both ways are correct as long as is not double bonded for it'll create parallel paths for ground and create a bigger hazard.
    Actually, the concern is a parallel pathway for neutral current on parts that should never carry normal current.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by jctj88 View Post
    As far as the OCPD for the distribution panel it does not have one buacuse it falls into the 240.21(C)(1)(2) rule, but if i'm wrong please let me know.

    240.21(C)(1)(2) is about protecting only the conductors on the secondary of a transformer.
    However, the panelboard also needs protection per 408.36, as others have mentioned.
    Just because you can, doesn't mean you should.

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    jim..

    i was talking about the secondary side of the transformer when i mention 240.21(C)(2) thats why i didnt put a OCPD on the secondary distribution panel, as far as the primary side of the transformer it is protected by a OCPD as well as the MDP.

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    Click image for larger version. 

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ID:	22959 This is how it looks. 600 amp MDP -->25kva transformer-->120/240v 125amp Distribution panel.

  10. #10
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    Quote Originally Posted by jctj88 View Post
    jim..

    i was talking about the secondary side of the transformer when i mention 240.21(C)(2) thats why i didnt put a OCPD on the secondary distribution panel, as far as the primary side of the transformer it is protected by a OCPD as well as the MDP.

    I know what used to be a common practice, but the panelboard cannot be a Main Lug Only design, since at least 2014. 408.36 requires the panelboard to have an overcurrent protective device. 408.36(B) requires the device to be located on the secondary side of the transformer.
    Just because you can, doesn't mean you should.

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