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Thread: 120/208 vs 120/240

  1. #11
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    Quote Originally Posted by Little Bill View Post
    Yes, but my reply was in thinking the OP was needing to have actual 240/120 voltages.
    I might have read him wrong as he could be asking about the panel rating only.
    His post states that he knows he will only get 208.
    The more they overthink the plumbing, the easier it is to stop up the drain

  2. #12
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    Quote Originally Posted by GoldDigger View Post
    But you can use a panel rated for 120/240 for a two out of three phase application. Just be careful with MWBCs.
    What is MWBCs?

    Sent from my XT1565 using Tapatalk

  3. #13
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    Quote Originally Posted by kda3310 View Post
    What is MWBCs?

    Sent from my XT1565 using Tapatalk
    multi-wire branch circuit
    Sometimes I don't know whether I'm the boxer or the bag.

  4. #14
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    Quote Originally Posted by JFletcher View Post
    Some 240V rated equipment will not be happy on 208V. A hearing test trailer should have 120V equipment for the testing, so whether it's fed from a 120/208 or 120/240V source *shouldnt* matter.

    As to your second question, residential service is often single phase (split phase or center tap neutral), with 120V to neutral but 240V line to line. Commercial transformers are often 3 phase and due to phase angle, 120V to neutral gives 208V line to line. There are open delta transformer banks that have 240V line to line, but the B phase is 208V to neutral. Why have 120, 208, 240, 277, 480V here? Different demands of equipment is one answer. A 900HP aeration blower would be wired to 4160V, you could wire it 480V or even 120V if you could make conductors that would carry 4,000+A. Cheaper to make better insulation and smaller wire.
    Just don't change the taps on the transformers, as I've seen done to get 240V on a three phase transformer (wanted the hot water heaters to heat faster). They had 130V to neutral, and didn't notice it for years.

  5. #15
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    Quote Originally Posted by kda3310 View Post
    What is MWBCs?

    Sent from my XT1565 using Tapatalk
    http://lmgtfy.com/?q=mwbc
    The more they overthink the plumbing, the easier it is to stop up the drain

  6. #16
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    Quote Originally Posted by kda3310 View Post
    I have to install a sub panel 120/240 single phase on to a 120/208 three phase system as per instructions of my boss.
    Mine just told me to drive to the moon to pick up some material. I'll get right on it boss...

    -Hal

  7. #17
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    Quote Originally Posted by hbiss View Post
    Mine just told me to drive to the moon to pick up some material. I'll get right on it boss...

    -Hal
    Green cheese?
    The more they overthink the plumbing, the easier it is to stop up the drain

  8. #18
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    Quote Originally Posted by kda3310 View Post
    I have to install a sub panel 120/240 single phase on to a 120/208 three phase system as per instructions of my boss. What I would like to know is there a problem with running 240 equipment on a 208 system and why do we have these two nominal voltage systems.

    Sent from my XT1565 using Tapatalk
    This is a pretty common practice in apartment buildings where all the loads in the unit are 120V.

  9. #19
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    Sep 2004
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    Norfolk, VA
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    Quote Originally Posted by kda3310 View Post
    This is our plant administration offices. It is all 3 phase 208. They want to hook up a mobile hearing test booth to it that has been running on a 1 phase 120/240 generator. I don't know what the both requires. I'm only doing what my boss is telling to do. I'm hoping there is not going to be any problems.

    Sent from my XT1565 using Tapatalk
    Every mobile hearing test provider I've had experience with wants 2 dedicated 120V circuits.

  10. #20
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    Quote Originally Posted by Mike Furlan View Post
    Just don't change the taps on the transformers, as I've seen done to get 240V on a three phase transformer (wanted the hot water heaters to heat faster). They had 130V to neutral, and didn't notice it for years.
    Quote Originally Posted by kentirwin View Post
    Every mobile hearing test provider I've had experience with wants 2 dedicated 120V circuits.
    Which makes sense. Some loads have a very abrupt load changes and cause a dip. You usually want equipment sensitive to sag and notching separate from house load to keep them away from notches and spikes.

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