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Thread: Reasons to get 480/240V single phase service?

  1. #1
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    Reasons to get 480/240V single phase service?

    I know this might be odd (or maybe not?), but I was considering requesting a 480/240 single phase service for a building. I will have multiple pieced of equipment, all running 240V, and all my lights running 240V. Basically I have very minimal 120V loads and considering just installing a 5kva transformer for 120V and eating the costs to keep it energized.

    Mainly I want to have my place "over wired" so when comes time for more power, the power company just needs to install a bigger transformer. I was going to get a 400A service. I realize I can just get 800A of 240V but that is twice the wire, well twice everything really.

    Or does 480V single phase gear command a premium being that it is less common? I planned to just run two, 200A panels with 4/0 Al triplex.

    Anything else to consider on a 480V service or system? I realize the dangers of 480V.

  2. #2
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    Depending on just what kind of "gear" you are thinking of, you may have a much harder time finding single phase 480 than single phase 240. I expect it to be less common and of course to draw more current than three phase. Not sure whether that would also translate to a premium price.

    PS: POCO may not want to deliver 240/480 single phase. You might get 277/480 from two out of 3 phases, similar to 120/208.

    Sent from my XT1585 using Tapatalk

  3. #3
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    You are going to pay more for 480V gear.

    The two reasons I have seen 480V single phase are
    1) To run a phase converter for an irrigation pivot where three phase is not available.
    2) To overcome voltage drop on a service to a building that was far from the power lines, so it was easier to step down the voltage once rather than step up and then step down.

    For single phase those are the only two reasons that make sense to me. 400A 240V service is a lot of power already. And while you acknowledged the danger of 480V may I just point out that my lineman relatives both admit to being happier working on kilovolt systems rather than 480V because it will sustain an arc better than anything above it or below it.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  4. #4
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    I should clarify this is a rural area where only single phase is available via 7.2kv primary, and that would be brought underground up to the building and a dedicated transformer set. Yep, I get to pay for that sucker! And I wanted to wait until the full effect of the hurricanes hits every price tag I get to pay for. Figures that when I need to buy, there is some market excuse why prices need to be inflated.


    I was planning to just install a 480 3P panel and not use one leg. I know we have a few around, fully loaded up. Of course I have not checked the code book yet and I am sure there is some reason I cannot do that. I can possibly see the breakers by having the dead circuit still poled on but but...... I mean with all breakers, if they are poled together, they are still designed where if one hits overload, they all kick down.

  5. #5
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    Quote Originally Posted by fastline View Post
    I was planning to just install a 480 3P panel and not use one leg. I know we have a few around, fully loaded up. Of course I have not checked the code book yet and I am sure there is some reason I cannot do that. I can possibly see the breakers by having the dead circuit still poled on but but...... I mean with all breakers, if they are poled together, they are still designed where if one hits overload, they all kick down.
    The standard name for that is "common trip".
    The disadvantage to using three pole breakers is that one failed circuit will trip the other too and when you want to work on a circuit you must turn off both circuits associated with that breaker.
    A simple handle tie between single pole breakers will not make them common trip, but you will have to turn all off to reset any one.

  6. #6
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    I'd suggest a load calculation for what you have now, and future loads.

    If the xfmr is being set in the building, the panels would presumably be close by, and having an 800A capable feeder at 240V vs 400 @ 480V would be a negligible cost in the overall equation. I dunno the difference in cost of gear, or if your lights (and other eqpt) are capable of running on 480V.

    eta: I would also consider the availability of a xfmr should yours go down.
    Electricians do it until it Hertz!

  7. #7
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    Also relevant to the design is the suitability of the equipment for connection to a 240V L to N supply rather than a 120/240V L-L supply.

    Because of _grounded_ input filters or transient voltage suppression, your equipment may not be happy with 240V L-N...or if the equipment is European in origin it migt be designed for 240V L-N.

    -Jon

  8. #8
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    Quote Originally Posted by ActionDave View Post
    May I just point out that my lineman relatives both admit to being happier working on kilovolt systems rather than 480V because it will sustain an arc better than anything above it or below it.
    That really depends also on the speed of operation of the associated protective gear. If the speed of operation of protective gear of the 240V system is slower than that of 480V system, it can have a more dangerous arc fault.

  9. #9
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    Dave, I am curious what loads you might be thinking of that would become problematic on 240V L-N? I can see your point as a device may normally connect a L-L with both lines being isolated from ground, then on a L-N, one leg of that would be the same potential as ground?

    Gold - I see what you are saying about the triple pole breakers. I forget I would only need a single pole for 240V loads. I guess I would have to source 480V breakers though, as typically they are 120/240. for 480 3P but I would think singles for 277V would still need to be rated for 480V being in that box?



    I could probably increase my entrance size I suppose, that way I would still be covered if we need to increase amperage, but 750mcm is NOT fun to work with and I know all the switch gear is going to get expensive.

  10. #10
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    Quote Originally Posted by fastline View Post
    Dave, I am curious what loads you might be thinking of that would become problematic on 240V L-N? I can see your point as a device may normally connect a L-L with both lines being isolated from ground, then on a L-N, one leg of that would be the same potential as ground?
    I also brought up the L-L vs L-N issue.

    Variable speed drives are a common example in 3 phase systems. These often have wye connected transient voltage suppressors connected line to _ground_. When these drives are installed on corner grounded systems the TVSs fail because of the voltage overload.

    While ground is not supposed to be used as a circuit conductor, it is commonly used as the reference for TVS and noise filtering devices. Because of this ground reference the system is not 'agnostic' with respect to L-L versus L-N supply.

    -Jon

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