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Thread: Transformer

  1. #1
    Join Date
    Aug 2007
    Location
    San Diego,CA
    Posts
    1,169

    Transformer

    Does anyone know off-hand what the +/- percentage of the secondary
    voltage is, when you tap up or tap down the primary on a transformer?

    480 primary/ 208 secondary

  2. #2
    Join Date
    May 2003
    Location
    Leesburg, VA
    Posts
    6,919
    Standard on small dry type is 2.5%.
    Brian John
    Leesburg, VA

  3. #3
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    8,580
    Transformers up to about 30kVA often have 5% taps. Above this the taps are usually 2-1/2% each. The quantities of taps are often +2 and -2 taps although +2 and -4 are not uncommon.
    Just because you can, doesn't mean you should.

  4. #4
    Join Date
    Aug 2007
    Location
    San Diego,CA
    Posts
    1,169
    Thank you both! I had just got a call about a voltage drop problem
    on a MRI fed from a common panel and I was thinking about re tapping
    the transformer. But, I could not remember if it was 2% or 20%
    increase/decrease,before I go out to do field testing, and even consider this
    an option. I'm suggesting a data log first. It's been a long day and here I go
    again.

  5. #5
    Join Date
    Aug 2007
    Location
    San Diego,CA
    Posts
    1,169
    False alarm.

    Facilities managers are servicing a compressor and have a rental
    compressor on site as stand-by. Guess what panel they chose to power it
    from? Compressor starts and the MRI gets 185 volts to do it's job.
    MRI's are corn fed,they need a full dinner to operate.

    Thanks for the help guys!!

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