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Thread: No primary protection required?

  1. #11
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    Quote Originally Posted by jumper View Post
    Well, when the electrician installs the required disco and OCPD, yout concerns will be gone.

    Besides that, I am not 100% sure about the first tranny OCPD protecting the conductors so landing them in an OCPD is a good idea.
    Here's the problem: cables between transformers on the 480V side have already been installed. Contractor doesn't want to spend the $ to fix it, so he's using his imagination to avoid the rework.

  2. #12
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    Quote Originally Posted by Isaiah View Post
    Here's the problem: cables between transformers on the 480V side have already been installed. Contractor doesn't want to spend the $ to fix it, so he's using his imagination to avoid the rework.
    Contractor really has no choice. Tranny has to have primary OCPD and disconnecting means. Fused switch or breaker can accomplish both.
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #13
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    Quote Originally Posted by jumper View Post
    Contractor really has no choice. Tranny has to have primary OCPD and disconnecting means. Fused switch or breaker can accomplish both.
    Thanks -

    Isaiah.

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    Quote Originally Posted by Isaiah View Post
    Thanks -

    Isaiah.
    No problem. Trust me, this site is totally pro, if I am wrong someone will call me on it.

    Let’s wait a few minutes and see if anyone does, but I am pretty sure I am correct.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jumper View Post
    No problem. Trust me, this site is totally pro, if I am wrong someone will call me on it.

    Let’s wait a few minutes and see if anyone does, but I am pretty sure I am correct.
    Here's the other part of the issue:
    Contractor bought a step-down transformer to utilize as a step-up ('flipped' it 180 degrees - secondary is now the primary @ 120V and primary is now secondary @ 480V). This is not considered a good practice since secondary windings are not normally suited to withstand inrush current as is the primary; plus 450.11(4) requires nameplate to identify primary and secondary voltages.
    The 480V side is also not grounded - 250.21(B) requires grounding detectors for ungrounded AC systems - another cost adder.
    To do this right, I believe he needs to replace the step-down xfmr with a true step-up, 120-480V and corner ground one side.
    Thoughts?

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    These are single phase transformers, correct?
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jumper View Post
    These are single phase transformers, correct?
    that's right.

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    Quote Originally Posted by Isaiah View Post
    that's right.
    I just PMed a friend who is better at designs than me.

    Hang tight.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    10-4, thanks

  10. #20
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    Quote Originally Posted by Isaiah View Post
    ....To do this right, I believe he needs to replace the step-down xfmr with a true step-up, 120-480V and corner ground one side.
    Thoughts?
    It's no problem to reverse feed a transformer. 450.11(B) makes this clear. Besides, it's only been recently that the code had anything to say about it at all and I don't think the manufacturers did anything different to their transformers other than add a note to the instructions that says, "It's ok if you want to backfeed this".
    If you don't think too good, don't think too much.

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