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Thread: different voltages

  1. #1
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    different voltages

    Does the 2017 NEC permit 110 voltage AC and 277 voltage AC in the same conduit if they are originated in the same lighting control panel where the 277 volt lighting circuitry is also stepped down to 110 for receptacles of the same lighting area serviced?
    All conductors in the same conduit are originated from the same Source lighting control panel and are insulated at 600 volts ac.
    All conductors are appropriately fused with circuit protection in the lighting control panel.

  2. #2
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    Yes. I don't have time right now to look up the relevant article. But as long as all conductors have an insulation system that is rated for the highest voltage in the conduit, you are allowed to mix voltages in the conduit. For your example, the conductors will all have a rating of 600 volts.

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    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  3. #3
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    You also would need to identify the neutral of each system. Typically one method is by using white for 120 volts and gray for 277. If the building has both systems then the voltage would likely be 208Y/120 so it's 120 volts not 110.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    300.3(C), 200.6(D) for those keeping score at home.
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  5. #5
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    Quote Originally Posted by infinity View Post
    You also would need to identify the neutral of each system. Typically one method is by using white for 120 volts and gray for 277. If the building has both systems then the voltage would likely be 208Y/120 so it's 120 volts not 110.
    Ungrounded conductors of each system need identification as well.

  6. #6
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    480Y/277V and 208Y/120V cannot be in the same panel. Raceways from each could go to a common j-box, then out from there to the loads served, so long as they comply with the aforementioned code sections.
    Electricians do it until it Hertz!

  7. #7
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    Quote Originally Posted by JFletcher View Post
    480Y/277V and 208Y/120V cannot be in the same panel. Raceways from each could go to a common j-box, then out from there to the loads served, so long as they comply with the aforementioned code sections.
    You sure about that?

    Remember a panelboard gets installed in a cabinet, so you are not so likely to land both systems on the same panelboard, but they can be in the same cabinet.

    There are "mini power zone" assemblies that have 480 volt primary breaker, transformer and 120/208-240 secondary panelboard all in one enclosure.
    Last edited by kwired; 09-11-17 at 09:39 AM.

  8. #8
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    Quote Originally Posted by kwired View Post
    You sure about that?

    Remember a panelboard gets installed in a cabinet, so you are not so likely to land both systems on the same panelboard, but they can be in the same cabinet.

    There are "mini power zone" assemblies that have 480 volt primary breaker, transformer and 120/208-240 secondary panelboard all in one enclosure.
    Yes they can occupy the same panel you would just need to identify the conductors that are passing through.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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