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Thread: Equipment Nameplate Marking - Larger or Smaller Voltage First?

  1. #1
    Join Date
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    Faribault, MN, USA
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    Equipment Nameplate Marking - Larger or Smaller Voltage First?

    This may be a simple question, but I'm having trouble finding an authoritative answer. Is there a UL or NEC document that requires whether the larger or smaller voltage comes first?

    For example, should a portable power distribution panel be marked 208/120V or 120/208V? Out of habit I've typically used the larger voltage first because that would usually drive component selection and spacing requirements. But I have not been able to find a written specification that requires one or the other.

    Thanks,
    Steve Takata

  2. #2
    Join Date
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    Quote Originally Posted by stakata View Post
    This may be a simple question, but I'm having trouble finding an authoritative answer. Is there a UL or NEC document that requires whether the larger or smaller voltage comes first?

    For example, should a portable power distribution panel be marked 208/120V or 120/208V? Out of habit I've typically used the larger voltage first because that would usually drive component selection and spacing requirements. But I have not been able to find a written specification that requires one or the other.

    Thanks,
    Steve Takata
    It depends on if it is single phase or three phase.
    One document to look at is the 'Red Book' IEEE STD 141 which is based on ANSI C84.1.

    The simple methodology is:
    For single phase systems use LV/HV, such as 120/240
    For three phase systems use HV/LV, including the symbol Y when applicable such as 240/120 and 208Y/120.

    Industry standards are really just suggestions, so it is likely you will find exceptions to this methodology.
    Just because you can, doesn't mean you should.

  3. #3
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    Oct 2011
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    Faribault, MN, USA
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    Thanks for the info. It has been the "standard" here for sales to write it LV/HV and for engineering to write HV/LV.

    So here's the most authoritative source that I can find on my desk -- Article 100 Definitions of NEC 2011. And it does agree with what you suggest. Good call!

    Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts).... Informational Note: See ANSI C84.1-2006, Voltage Ratings for Electrical Power Systems and Equipment (60 Hz).
    I figure if NEC and the NEC Handbook authors use this standard, it's good enough a standard for me.

    Steve

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