Why 277 volt lighting?
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  1. #1
    Join Date
    Mar 2002
    Leesburg, VA USA
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    Why do so many commercial buildings use 277 volts for their fluorescent and metal halide lighting power? Much of the surplus light fixures one comes across are 277 volts.

    I don't understand this. Is the concept that you get 277 volts across 2 legs of 3 phase power? I don't think that is the case.

    Do they run these through transformers? If that is the case, that seems really silly because you loose effieciency in a transformer, not to mention being another point of failure and fire hazard.

    So- how are 277 volt fixtures wired in a commercial setting? And is it reasonable to consider powering them somehow from 240 single phase either directly or via a stepup transformer?

    I am trying to put together a case for the local power company to provide a 3 phase drop to my barn. They run their @#$%^ power lines right across my farm and maybe 30' from the barn. I'd like to be able to justify to them why they should give me the drop (" i have the following 3 phase motors on machines, and my shop lighting is 277 volt")...but I don't know how you power 277 volt lighting, or if its reason for being is related to 3 phase.

  2. #2
    Join Date
    Dec 2004
    Sterlington, LA
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    277 Volts is the voltage between any phase of a 440 volt wye connected 3 phase service and neutral. This is the reason for 277 volt lighting systems in industrial and commercial settings.

  3. #3
    Join Date
    Dec 2002
    Monterey Bay, California
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    "277 Volts is the voltage between any phase of a 440 volt wye connected 3 phase service and neutral. This is the reason for 277 volt lighting systems in industrial and commercial settings."

    480 volts was the logical upgrade from 240 volts.

    480 volts is occasionally found in a Delta system, but this is most often found in a 277/480 volt Wye system.

    There are two general insulation classes in North America for secondary systems: 300 volt class, 300 volts to ground, or less; and 600 volt class, 600 volts to ground, or less.

    (Another insulation class is the so-called SELV, which is 48 volts to ground, or less).

    277 volts falls within the 300 volt class, and a special wiring system is not required to install such a branch circuit. This is the reason 277 volt commercial/industrial lighting is so popular.

    110/115/120 (125 volts max), 220/230/240 (250 volts max) and 440/460/480 (500 volts max) are some nominal secondary voltages found.

    However, the 277/480 Wye system is 480 volt based, just as the 120/208 Wye system is 120 volt based.

    In most commercial and industrial premises, 120/208 or 277/480 is found, and any required 240 is provided by a customer-owned "dry type" transformer.

    At my former employer, this nation's largest municipal electric utility, 240 Delta and 480 Delta were "grandfathered", and service upgrades were expected to be 120/208 or 277/480, with other voltages being possible provided the customer paid for the distribution transformer and provided a dedicated pad or vault for such transformer. (Our primaries were either 4,800 volts or 34,500 volts, at our option).

    (120/240 single-phase is still standard for single and multiple unit residences, except for larger apartments where 120/208 three-phase is generally found).

  4. #4
    Join Date
    Apr 2005
    South of Atlantic City NJ
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    Hi all, I'm not an electrican so I ask at the electrial supplier about install 240 volt lights in my garage. The voltage on the light read 277 volts I power them with single phase 240 volts and they work fine. Anything I should be aware of?


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