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  1. #1
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    Jan 2020
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    Question regarding multi tap transformer.

    Hello all,
    Hopefully this is the correct place to post this thread, and I apologize if this question has already been answered. I’m performing start up on 2 residential style 4 ton split systems at a factory that will be opening shortly, and my power supply is 208v. The transformer for these electric furnaces are multi tap style transformers, and are currently connected to the 240v tap, instead of the 208v tap. I understand 240v is more for a single phase residential application and that 208v is 2 legs of off a 3 phase power feed. I want to know if the resistance is actually different off of the 208v tap compared to the 240v tap, and what effect it will have on the relays and contactor coil, if the transformer tap isn’t switched to 208v to match the supply voltage.

  2. #2
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    Aug 2006
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    If you have a primary lower voltage than the transformer is rated for, you will put out a lower secondary voltage. If you have the ability to change the tap to a more accurate entering voltage, then do so.
    "Right" is not the same as "Wise".

    Don't step on my favorite part of the Constitution just to point out your favorite part.

  3. #3
    Join Date
    Nov 2011
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    It’s a given that the resistance of the two taps is different.

    If you want to learn more about transformers, google search “transformer Turns Ratio”.

  4. #4
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    Jan 2020
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    Central Indiana
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    Thread Starter
    I pointed out to the journeyman that I was working with today that the panel was labeled 208v and the wiring schematic in the unit showed that it comes from the factory wired for 240v. I mentioned moving the wire connection to the 208v tap and he told me it doesn’t matter. Thank you for the replies, that’s bugged me all evening.

  5. #5
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    Jan 2020
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    Central Indiana
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    Thread Starter
    Quote Originally Posted by 71CHOPS View Post
    It’s a given that the resistance of the two taps is different.

    If you want to learn more about transformers, google search “transformer Turns Ratio”.
    That helps, thank you.

  6. #6
    Join Date
    Aug 2006
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    Quote Originally Posted by jgriffey322 View Post
    I pointed out to the journeyman... I mentioned moving the wire connection to the 208v tap and he told me it doesn’t matter....
    It does matter but he is in charge and responsible for the job so leave it alone.
    "Right" is not the same as "Wise".

    Don't step on my favorite part of the Constitution just to point out your favorite part.

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