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Thread: 120/240 Three Phase Transformer

  1. #11
    Join Date
    Apr 2009
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    Williamsburg, VA
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    Quote Originally Posted by Jraef View Post
    I didn't know (or maybe remember) any of this until late in my career when I went to work for Siemens in 2006. I attended a training module on Switchgear and Transformers and thought "I can teach this, I'll just sleep through it and ace the exam." I got that wrong on the exam, which forced me to go back through some of the stuff I slept through and there it was; something "new to me".

    Like I said, the convention makes sense, but few people adhere to it, so it's mostly a convention in name only. Kind of like Switchgear and Switchboard, which have specific official definitions, but most people use the terms interchangeably. So if you are a stickler and try to correct everyone that uses the terms wrong, nobody wants to talk to you twice...
    Like how people wrongly call 8p8c plugs/jacks "RJ-45".
    Electricians do it until it Hertz!

  2. #12
    Join Date
    Feb 2003
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    Wisconsin
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    Quote Originally Posted by Jraef View Post
    Just FYI for the naming convention (per IEEE):

    • If discussing THREE phase systems, you always put the Line to Line voltage first, as in 208Y120 or 208/120; 480Y277 or 480/277; or in this case, 240/120V 3ph 4 wire.
    • If discussing a SINGLE phase service, you always use the Line to Neutral voltage first, as in 120/240V.


    Case in point, per the IEEE rules the title of this thread is technically incorrect... In discussing the service transformer, it would be described as a 240/120 3 phase 4 wire delta transformer.
    But in the wolrd of Power Companies/Utilities, the IEEE designations are not commonly used. If you look at Cooper utility transformer literature it seems to be based on the type (one or two insulated connections) of single phase transformers which could be used to create the three phase service.

    Also, I first sold a slash rated 480Y/277V breaker when Square D introduced their NEHB lighting panel in the early 80's.
    Just because you can, doesn't mean you should.

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