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  1. #14
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    I have run into those situations when where the input voltage on a transfers is hooked onto the 240 when in reality it should have been hooked to th 208 leg which is th supplied voltage. Don't know why people do it but it sure gets screwy as the unit ages





    QUOTE=timebuilder;24795681]I have seen this overlooked for so many years I can no longer count the number of instances I have found this one issue.

    It should never be overlooked.

    It is SO quick and easy to do.

    And, you won't look like you were standing in front of a Home Depot that morning.

    Please.

    Set the right voltage.

    I know no one is mentioning it. That part is obvious. Let me explain.

    When three phase units are tested at the factory, they are using a three phase Delta supply. So, the factory is testing the unit with 240/3 volts. At one time, this was the same voltage being used in the three phase world of commercial and industrial power.

    This is no longer the case in most places.

    Today, the end use voltage is either 460/480 (and they make no distinction between those levels, as 480 is the new 460, due to rising feeder voltages) or 208/230 (or, 240).

    And that second group is the issue here.

    What used to be a Delta power setup is now more frequently a Wye setup, and as many of you know, a transformer tapped for a Wye output in this voltage range is going to have a target voltage of 208.

    Most of the time, you will have a control transformer with a 230 tap and a 208 tap. Before you leave, make sure the correct tap is selected. Easy peasy.

    Now, for you Trane guys, you have a second transformer, which is used for the hot surface ignitor and sometimes other loads. That transformer comes from the factory with the load group connected to H3, which is the 230 volt input tap. In order for the HSI and other output needs to be properly met, that primary terminal group needs to be moved over to H2. It's right in the notes on the wiring diagram.

    Once again...it's easy.

    So, in summary...

    ...make the contactors and ignitors and everything else in that unit get off to the right start, so that as the HSI ages, it can work longer, instead of being starved for source voltage, which reduces the current to the point that the HSI can no longer light the gas mixture.

    Commercial installers...stand up and do a Pro job.

    End of electrical rant for today. [/QUOTE]

  2. #15
    Join Date
    Nov 2006
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    Thread Starter
    Here's another little tidbit:

    on the 480-volt units, the transformers often have a 575 volt tap, which obviously you do not want to be using when you have a 480 volt supply.

    I like to take an insulated sta-kon terminal and plug it on to the unused tap tabs...because the unused tabs are hot.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
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  3. #16
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    Sep 2002
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    Why is so little 575 used in the US? At one time I used to see more and more of it and at the time concluded that it was likely to be a growing trend. But apparently the idea of a 600 volt system never spread. Now that I'm thinking about it - 575V used two difference frequencies too. 25 and 50hz I don't know why though.

    In Europe 240V is generally the lowest voltage available and all seems to go well. In the US we could cut all the wire gauge requirements in half if we standardized at 240 instead of 120. Hey; maybe the copper lobbists are more powerful than we ever suspected? <g>

    PHM
    --------



    Quote Originally Posted by timebuilder View Post
    Here's another little tidbit:

    on the 480-volt units, the transformers often have a 575 volt tap, which obviously you do not want to be using when you have a 480 volt supply.

    I like to take an insulated sta-kon terminal and plug it on to the unused tap tabs...because the unused tabs are hot.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  4. #17
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    Thread Starter
    They are very powerful.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
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  5. #18
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    Apr 2003
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    Maple Grove, MN
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    Well we're on the subject, Heatcraft has some walk-in freezer evaporators that have circuit boards and electronic expansion valves in them. I can't think of what they're called but they're really slick if you run into them.

    Anyways, there is a transformer in those things that needs the incoming voltage to be on the right tap also.

    Good post, Timebuilder. This is something that I see that gets missed all of the time too.
    If at First You Don't Succeed, Skydiving Is Not for You.

  6. #19
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    Thanks. I'm venting...with a purpose.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  7. #20
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    Quote Originally Posted by Poodle Head Mikey View Post
    Why is so little 575 used in the US? At one time I used to see more and more of it and at the time concluded that it was likely to be a growing trend...
    Just throwing this out there...could it be that anything over 600 VAC is considered medium voltage? I don't know if over 600 is considered medium voltage or not, however, I see 600 VAC used a lot in literature as the upper threshold when talking about voltage ranges. While 575 VAC is the nominal value, the line voltage could easily surpass 600 VAC under certain circumstances.
    Don't step on my favorite part of the Constitution just to point out your favorite part.

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  8. #21
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    A lot of electrical devices and tools used in the US are listed for up to 600 volts. That may figure in....
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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