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Thread: Unusual Question - Powering a single phase panel with 120 Volts

  1. #1
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    Unusual Question - Powering a single phase panel with 120 Volts

    I have a design I am completing which will be installed in various locations around the US for the Federal Government. The installation will be at radio station tower locations.

    There is a 30 amp 120 volt feed and I need two 20 amp 120 volt circuits powered through this feed. The 30 amp circuit is capable of handling the loads as they are minimal wattage for each item. (1200 watts for one and 600 watts for the other)

    I need a means of disconnect and the items are both required to be on a 20 amp max disconnect per the manufacturer. I have two thoughts for how to do this (other than in-line fuses which I don't like and do not want to use)

    1 - Install a single phase panel and power only one leg of the panel
    2 - I have seen some din rail mounted circuit breakers that could be placed in a Hoffman enclosure, but I do not think they are code compliant due to the fact that the Hoffman enclosure is not UL listed for that purpose and the cover must be removed to access the breakers

    So, does anyone know if I can power a single phase panel with 120 volts? or am I mistaken about the Hoffman enclosure? Thank you in advance for your help.

  2. #2
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    I would get a small 240/120 panelboard and just jump the incoming terminals on the main together and feed it with 120V.
    Bob

  3. #3
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    I've looked at powering 1 phase of a panel before but it seem like it gets messy and would need lots of labeling.
    You could use 2x enclosed circuit breakers tapped to the feeder. Or even a 2 pole 240V/20A with both poles tied to the same hot.
    For 1800W of load you would only need 1x20A circuit which is even simpler.

  4. #4
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    Quote Originally Posted by sheldonrf View Post
    There is a 30 amp 120 volt feed and I need two 20 amp 120 volt circuits powered through this feed.
    Why cant you just replace the 30 amp 120v feed with (2) 20 amp 120v feeds from the panel that the 30 amp feed is coming from already ?


    JAP>

  5. #5
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    Quote Originally Posted by jap View Post
    Why cant you just replace the 30 amp 120v feed with (2) 20 amp 120v feeds from the panel that the 30 amp feed is coming from already ?


    JAP>
    It is complicated, but it is what must be because the power is an output from a "black box" so to speak.

  6. #6
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    Quote Originally Posted by sheldonrf View Post
    It is complicated, but it is what must be because the power is an output from a "black box" so to speak.
    Almost sounds like a 20 amp circuit would handle both of those small loads.

    Change the 30 amp CB out to a 20 amp, and rock and roll with the new 20 amp branch circuit.


    JAP>

  7. #7
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    Run your 30 amp feed to a 6 breaker sub panel. Power one side of the bus. Install 2 20 amp Breakers that are powered from that bus. Done.

    You can use three phase panels for single-phase applications, and you can use a split phase panel with just 120. No special labeling required unless perhaps you put a jumper across from A to B, which is unnecessary here anyway
    Electricians do it until it Hertz!

  8. #8
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    Quote Originally Posted by JFletcher View Post
    Run your 30 amp feed to a 6 breaker sub panel. Power one side of the bus. Install 2 20 amp Breakers that are powered from that bus. Done.

    You can use three phase panels for single-phase applications, and you can use a split phase panel with just 120. No special labeling required unless perhaps you put a jumper across from A to B, which is unnecessary here anyway
    There's a special brand name for the panels used in this type of installs.

    They're called Whodoneits.


    Jap>

  9. #9
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    Quote Originally Posted by sheldonrf View Post
    There is a 30 amp 120 volt feed and I need two 20 amp 120 volt circuits powered through this feed. The 30 amp circuit is capable of handling the loads as they are minimal wattage for each item. (1200 watts for one and 600 watts for the other)
    I have seen this exact setup a few times. Its NEC compliant. A 30A 120V feeder going to a two circuit loadcenter, hots jumped together on the main lugs. These had a 1 pole 20A and a 1 pole 10A. I remember thinking it was odd every time and looking it up. When we demoed one out I kept the 10A plug in circuit breaker because I had not seen one before. It is now in my odd breaker collection.

  10. #10
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    Quote Originally Posted by tortuga View Post
    I have seen this exact setup a few times. Its NEC compliant. A 30A 120V feeder going to a two circuit loadcenter, hots jumped together on the main lugs. These had a 1 pole 20A and a 1 pole 10A. I remember thinking it was odd every time and looking it up. When we demoed one out I kept the 10A plug in circuit breaker because I had not seen one before. It is now in my odd breaker collection.
    Click image for larger version. 

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ID:	20128Siemens 10 amp single pole breaker. Click image for larger version. 

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ID:	20129 SQ-D 10 amp single pole breaker. Both under $5 at wholesaler's.
    85deg. an Sunny today.

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