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Thread: Questions on 120v loads on a 120/208 3 phase panel with NO 3 phase loads? Panel size?

  1. #11
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    To add to what jflecther and kwired have said:

    By assigning kVA values to all the loads and then distributing them, you will be able to work with single and three phase loads and panels.

    Most panels are goings to be a combination of loads and if you do it this method we are trying to show you, it will always work.
    "Electricity is really just organized lightning." George Carlin


    Derek

  2. #12
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    Quote Originally Posted by jumper View Post
    You cannot add the amps that way. Period.

    Your 97A total is incorrect.

    Are all your loads continuous? Why the .8?
    Okay from spec sheets it comes to 97.1 if added together (I'm listening to try and learn why this isn't correct)


    Yes the loads are continuous or all on when open for business.

    /.8 = panel size 125% of load
    Last edited by re-evaluating; 01-05-18 at 01:45 PM.

  3. #13
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    Quote Originally Posted by JFletcher View Post
    Welcome to the forum. You need a 3ph panel that can carry the maximum load per leg, which as kwired calculated was 33.33A. A 60A panel is more than capable of that. You need a minimum 5 wire #8 feed, which sounds terribly small for a commercial kitchen; what are the exact loads you have?

    Three phase power is kw = VL-L x I x pf x √3 ÷ 1000 or kW = (VL-L× I × PF × 1.732) ÷ 1,000.

    As mentioned above, you cannot add amps, tho if each line were perfectly balanced, you could use total kW or kva with the above formula, reworked as such:

    I = KW ÷ (VL-L x √3 x PF )

    In other words, if you had a single 11.5kW 3ph 208V load, it would draw 31.9A per leg. If you were sizing a breaker for this, and it were a constant (continuous) load, you'd need a 40A breaker, and #8 wire.

    A 60A 3ph panel is plenty for what you list. Is this a package kitchen, like what would be on a food truck? I ask because a single 208V 3ph commercial deep fryer can pull 40A (11.5+kW) on its own. It looks to me you have 6 208V 1ph loads and 1 120V load to 13 120V loads that are all relatively small.
    No this is a Chef's counter with 13 120v circuits 8 inductive warmers 4 @(1100w) and 4 @(950w) 2 refrigerators @(876w) 1 freezer @(924w) and 2 printers @(360w).

    Thank you for taking the time to help me understand the concepts here. Here is the layout.
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  4. #14
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    Re-evaluating, the only time you add amps is when dealing with equipment on a single line. Example: you have 12 1.5A and 6 1.0A loads, all 120V. In that case you have 24A total @ 120V. Now, if you had a 1 ph panel, and the loads were balanced, you would have 6 1.5A and 3 1.0A per leg, or 12A total, at 240V. If you had a 3ph panel that was balanced, you'd have 4 1.5A and 2 1.0A to give (you'd think) 8A per leg, but across 208V, not 360V. The ONLY way this works tho is factoring the varying voltages; you are no longer working with 120V in all 3 cases:

    24A @ 120V = 2880W - 24A on a single 120V circuit
    12A @ 240V = 2880W - 12A on a 240V circuit
    8A @ 208V = .... 1664W... oops! when working with three phase, we have to multiply by the square root of 3: 1664 x 1.73205... = 2880W, or 13.8A

    eta: just saw your above post. Yes, everything there is correct. To answer again your initial post, a 60A 3ph panel is plenty for your application.
    Last edited by JFletcher; 01-05-18 at 01:59 PM.
    Electricians do it until it Hertz!

  5. #15
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    Quote Originally Posted by re-evaluating View Post
    ...my panel supplier keeps telling me that I have to account for total amperage when sizing this panel (97.1/.8=121.4amp = 125amp panel)....
    You need a new panel supplier.
    Just because you can, doesn't mean you should.

  6. #16
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    Your panel supplier is incorrect in adding amperage for three phases together. kwired was correct on his first post. With 33.33A being the highest leg and adding 25% to all on this leg for continuous duty, highest case scenario is 41.66A. The 60A 120/208V 3-phase panel will work fine!

  7. #17
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    And my POCO representative tells me that I should always run the heat and the A/C at the same time so I have a zero energy balance.

  8. #18
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    Never mind.
    Last edited by infinity; 01-05-18 at 05:54 PM. Reason: Removed confusion
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  9. #19
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    Quote Originally Posted by infinity View Post
    Never mind
    Rob, please do not go there.

    I and many members here will understand your point, but that is not the proper way to learn load distribution.

    That idea could work here if one knows all what applies, but the full method always works.

    Throw in one 20A 208V single or three phase load and it goes kaput.
    Last edited by infinity; 01-05-18 at 05:55 PM. Reason: Removed confusion
    "Electricity is really just organized lightning." George Carlin


    Derek

  10. #20
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    Never mind.
    Last edited by infinity; 01-05-18 at 05:53 PM. Reason: Removed confusion
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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