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480-4wire service

Discussion in 'Electrical Engineering' started by User 1.nospam, May 25, 2004.

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  1. I saw a new one (to me) yesterday. Trouble shooting an aircompressor
    control panel I got strange readings on the incoming line to ground. I had
    thought it was a standard 480Y277 service. On one leg to ground I got

    I thought I was familiar with all the different configs available in the US,
    so imagine my surprise when I examined the three xfmrs on the pole and
    discovered that they were connected 480 delta and that one of them had a
    center tap, which created a neutral, hence the 242 volts. The connections
    could have easily been for 240, 4 wire, which is fairly common here, but it
    is definitely 480-4wire. The installation is about 10 years old.

    I have done electrical work in this area (Kentucky) for 30+ years and this
    is a first. So I ask, anyone else ever seen this? What applications does
    it have? Is it common anywhere?

    Maybe the power company ordered the wrong xfmrs, or got a real deal on a
  2. John Gilmer

    John Gilmer Guest


    Yes, but ...

    Are not these arrangements accomplished with just TWO transformers in a "dog
    leg" configuration?

    The "special" problem is the 3rd phase which is supplied by the smaller
    transformer. A significantly lower interrupting capacity when used in a
    "supply" that can't supply much current, isn't much of a risk, is it?

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