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Wye 3 phase to single phase distribution woes

  1. Jan 13, 2010 #1
    I have a 125amp, 240v three phase circuit feeding a 30 kva UPS through a delta/wye transformer, leaving 208/120v three phase entering my panelboard. I plan to use 50 amp, 3 pole breakers, with a neutral and ground, making 5 wire three phase.

    My question is: When I bring the 5 wire, three phase out to the field, I want to make three, single phase, 120vac circuits. Can anyone provide feedback, parts that could make this happen, or tell me im nuts and then offer another solution?

  2. jcsd
  3. Jan 13, 2010 #2
    You won't bring the three phase out into the field, you will have single phase circuit breakers in your panel board that supply single phase (Active, Neutral and Earth) supplies to the equipment. The active is one of the phases that has been brought into the board. Each circuit can be on a different phase.
  4. Jan 13, 2010 #3
    Im bringing the three phase because the runs are over 1000 feet. Im going to run awg 4 stranded copper wire to reduce voltage drop.

    Is there a panelboard that will accept a 3 wire three phase main, provide a nuetral and ground bar, and have single phase breaker outputs that will ensure balanced loading throught the phases?

    A model number would be appreciated if this exists, or i may just be retarded
  5. Jan 13, 2010 #4
    I can't help with a model number, I live in Australia, but what you have described is what happens most of the time in panel boards, 3 phase in/single phase out. If you are supplying 3 pieces of equipment then its easy to put each one on a different phase. As for balanced loads, it depends on when the equipment runs.
  6. Jan 13, 2010 #5
    the equipment runs 24/7 but it has different loading at different times.

    btw, is your name a jay and silent bob quote?
  7. Jan 13, 2010 #6
    Yes it is, I have been using it for a very long time.

    There isn't much that can be done about balance at the design phase other than trying to spread the loads as equally as possible. If it is going to be a problem, the use of 3 phase equipment should be considered (if possible).
  8. Jan 13, 2010 #7
    the 120v feeds from the 3 phase sub panel are going to equal transformers, perhaps a 1kva 120v/24v transmformer. These are all identical.

    Would it be better to run a different UPS? Possibly a 240v 2-phase (L,L,N,G, if thats even right) circuit to the distribution for 120v circuits?

    I ultimately need 120v at the field locations, which are far from the UPS. What do you think?
  9. Jan 13, 2010 #8
    Chances are the loads if only 1kVA aren't going to be much of an issue for balance. There is always inbalance.
  10. Jan 13, 2010 #9
    Thanks, appreciate the advicer
  11. Jan 18, 2010 #10
    Yes, they make 208Y/120V panelboards. There are 3 line lugs (one for each leg of the 3 phase). There is also a neutral bus bar and a ground bus bar which should not be bonded together since, in your case, this will be a sub panel (this should only be done at the main panel).

    They are quite common. All the major companies dealing with electrical distribution carry them (G.E., Square D, Eaton, Siemens, etc.)
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