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QOTD: Leaving a phase out

Discussion in 'Question of the Day' started by Footer, Nov 22, 2011.

  1. Footer

    Footer Senior Team Senior Team Premium Member

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    STUDENTS ONLY

    During the in for a tour, the head elec hands you a distro and asks you to tie it in. When you look at it, you realize it only has 4 male Cam-loks, one green, one white, one black, and one red. Your company switch has 5 cam females, one green, one white, one black, one red, and one blue.

    How do you proceed and why?
     
    Last edited: Nov 22, 2011
  2. 65535

    65535 Active Member

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    My thought is that you can safely omit a phase and wire it up as the split-phase the distro was designed for with.

    Other than loading the 3 phase transformers odd I don't see a problem. I know our shop uses 1 leg of the 3 phase supply to run sometimes grossly unbalanced loads at 208V transformed to 220V (ok so it's really more like 218.4V depending on how stable the phase is) for stationary saws and welders.

    Considering most applications feed 3phases around the building chopped down to single phases per load. I don't see it being a problem.

    The only alternative I could think of would be to acquire a 3phase 5 wire distro and balance the loads.
     
    Last edited by a moderator: Nov 22, 2011
  3. mstaylor

    mstaylor Well-Known Member Departed Member

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    Just remember proceed doesn't necessarily mean go hook it up, it can but maybe there is something else.
     
  4. esmphoto

    esmphoto Member

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    Seconded.,
    My first thought on reading the question was that I didn't know what the heck you were talking about.
    Given that most of the pros I get to work with undertand that I'm a student I'd probaby find someone and ask, I'd rather someone know that I didn't know than do anything wrong with three phase power.
     
  5. headcrab

    headcrab Active Member

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    Just because the power is available (or the connector is there) doesn't mean you have to use it. Loading two out of three phases won't necessarily damage anything, though the POCO may hate you for it.
    I'd connect as normal, matching colors on the distro to the switch, but ignore the blue phase (c?) on the company switch. It would not have anything connected to it.
    When loading the distro, one would have to keep in mind that the phase-to-phase voltage is 208V and not 240.
     
  6. chausman

    chausman Chase Fight Leukemia

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    Well, this might not be what Footer meant by asking the question, but for me, if I was told to do something I wasn't sure of, I would ask someone else to do it correctly (and safely), and show me how.

    I do know somewhere we've talked about not using all the Cams on here before.
     
  7. porkchop

    porkchop Well-Known Member

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    Footer should the assumption be made that the gear is from the US (i.e. US color scheme and 3 phase WYE?) or are we thinking about the wide variety of touring gear out there?

    You're very unlikely to find this phase-to-phase voltage anywhere unless you have specific transformers for it.
     
  8. epimetheus

    epimetheus Active Member

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    I'm not sure I understand your statement here. 208V and 240V are probably the most common phase-to-phase voltages available in the US.
     
  9. porkchop

    porkchop Well-Known Member

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    240V is a common phase to ground or neutral voltage in lot of countries other than the US, but in the US it's hard to get 240V unless you are using both sides of a single 120V transformer. In that case you would get 240V between phases but they are 180 degrees out of phase not 120.
    That's not really useful for show power. It's done in residential and industrial installs but that's not what we're talking about here. To be honest this isn't really the point the first half of the post was the more important part.
     
    Last edited: Nov 23, 2011
  10. rochem

    rochem Well-Known Member Premium Member

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    Well I mean, "say no and locate a qualified person, per the NEC to do it" seems like a reasonable answer to the question. But I don't think that's what you're looking for, is it? Or do you want an answer like "run and hide, he's gonna blow his stuff up!"?

    Not totally related, but I came across a block full of television trucks and their thousands of feet of feeder today in manhattan. Found a particularly interesting spider box on a corner, which not only had the connections into the box completely submerged under 7-10" of water, but also the electrician apparently decided he didn't feel like plugging in the ground, and it was just kinda sitting there underwater. I tried to take some photos, but they all came out blurry and obscured from the pouring rain.
     
    Last edited by a moderator: Nov 23, 2011
  11. avkid

    avkid Not a New User Fight Leukemia

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    Outside MSG?
    Those TV trucks do some weird stuff.
     
  12. epimetheus

    epimetheus Active Member

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    Your right voltage differences between countries and the arrangement of 120/240V split-phase, of course, but in regards to Footer's original question (and I hope I'm not giving too much away here), the most common reason someone would be in the situation of hooking a 5 wire company switch up to a 4 wire panel would be the instance of a 120/240V split-phase service.

    Also, I disagree with your statement that 120/240V split-phase is not useful for show power. Though I feel I can't explain any further without totally giving away the answer to this QOTD.
     
  13. porkchop

    porkchop Well-Known Member

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    If it's a 5 wire company switch you're talking about 120/208V. That was my point.
     
  14. DuckJordan

    DuckJordan Well-Known Member

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    not to muddy the waters further but for those of you who say hook it up as is, What do you do with the now open hot?
     
  15. drummerboi316

    drummerboi316 Member

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    Stand in a puddle and lick the inside? :twisted:
     
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  16. 65535

    65535 Active Member

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    Ground it of course....

    At least on our company switch and others I've seen they all had covers over the connectors.
     
  17. Sony

    Sony Active Member

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    I've seen some pretty sketchy company switches that are just basically tails hanging out of a disconnect. Not all company switches have covers.
     
  18. ejsandstrom

    ejsandstrom Member

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    Just curious why no one has suggested measuring the voltage? Why assume? I have had to use all of the above colors for various voltage connections.
     
  19. mstaylor

    mstaylor Well-Known Member Departed Member

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    As somebody that hands tails like this to building electricians and also receive them as the building electrician, there is a very basic thing that has to cleared up, what type of hook up is needed. When I hand four wires to be hooked up I tell him whether I want a single phase,nuetral and ground or three phase, three hots, no neutral and a ground. If I am recieving tails I ask what he wants, then I tell him to come visually inspect it and meter it before attaching to his gear.
    If you are hooking up single conductor cables, then you should know your tie ins and shouldn't have to meter it. If you don't already know then you don't meet the defination of qualified person. Now if you happen to be tapping a generator then absolutely check voltages.
    If you are doing a single phase tap, then either cap the spare leg or tape it off so it can't be touched.
     
  20. SteveB

    SteveB Well-Known Member

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    It's been a week and as the QotD is usually a week for students, I'll throw in my thoughts.

    1) If you are not the person designated and/or the person with the skill and authority to do tie-ins, politely inform the event electrician that you will get the correct person to do the tie-in. You work for the house, so follow the rules of the house.

    2) Double check that the person that handed you the tails is the person with the event that actually knows what kind of power they need. Verify what they need.

    3) Verify that the tails being provided are color coded correctly for the event equipment. If in doubt, have the person from the event hand you a Hot when asked, then another Hot, then the Neutral then the Ground. This way the event personnel are responsible for their own gear if they were in error. Big red caution lights go off in my head when I see Cam-Lok connectors that are covered in vinyl colored tape of a different color then the Cam color, makes me ask WHY ?.

    4) Connect as per color once all concerns are addressed, or connect as per the event electricians direction. If something seems amiss, be prepared to meter the tie-in at the tails.

    5) If the blue is not used, either cap it or if no capability to cap exists, open up the company switch and remove the blue feed wire from that phase lug. If the switch has live wires, switch off at the appropriate breaker, lock and tag prior to working in the disconnect. If the blue tails wire is bundled, mark it with a "Not Used and Connected" flag, white 2" gaff would be my choice.

    In truth, I run into this all the time with audio gear and simply cap the non-used tail. If it's a one-off I rarely mark it (my bad) as I'm the only electrician dealing with the tie-in.
     
    Last edited: Nov 30, 2011

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