220 single phase drop

Discussion in 'General Electronics Chat' started by explorer12, Nov 27, 2008.

  1. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    Can someone please help me. I am in the US. I have to make a single phase 220v drop from overhead bus bar. I dont know the rating for the bar. To power a rectifier for a test. I am using 12/3 black cord and a strain relief. The black cord has a white, black, and green wire. At the rectifier there is places for 2 lines in and a ground simple. At the bar is where i get confused there are 4 lines inside the top one is for common white wire. The green ground wire grounds to the box. I need to know if Iam doing this right by puttting white wire to top bar, the black one of the other three bars, and the green to the box. This is a circuit breaker protected box. I was going to use 20 amp breaker here is where i get confused again I have options to put in one to three circuit breakers. Should i just use one breaker on the black wire? The white wire /common has no place for a breaker. I dont think it needs one. If i am correct how do i know it is single phase 220v. thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    You did not mention the colors of the wiring inside the channel. If it is to code, then green is the protective ground. White is the AC common. Another wire should be black. That is one AC hot The remaining wire should be red. That is the other hot phase.

    Measuring black to white (or red to white) should show 120 VAC. Red to black should be 240 VAC.

    Your drop cord is only rated for 120 VAC. The green lead is ground. White is AC common, and the black is the hot phase. You can always wire the white to red for 240 VAC through the cord, but it is bad practice to do so. Any drop from a bus should have a red lead present for the other hot phase. The next best thing is to use tape on the exposed insulation (red) as a signal that it does not carry AC neutral.

    If you are sourcing 220 VAC, then two breakers are necessary - one for each hot phase. For proper protection, they must be linked so one tripping also trip the other. A third breaker in the common line could trip, leaving both hot phases still present - that is a lethal situation.

    If the situation is controlled, it is, perhaps, up to you. But is anyone else is likely to come along later and use that drop, he might look at the lead colors and assume 120 VAC when you have it wired to 240. That could lead to lethal situations and/or destruction of equipment.

    You do not indicate any galvanic isolation being used. That means that every lead into or out of that rectifier should be considered to have 120 volts on it, and be a lethal shock hazard. If this is for some company usage, they are in violation of the NEC.

    By all means, use a meter to verify which line is which up in the bus run before proceeding.
     
  3. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    Cant see in channel. There are four openings in the channel (lined up from top to bottom) where the box plugs or clips on to the channel. Could be metal rods inside not wire colors. Top line connects to neutral/white wire bar in box. Are the other three hot? Is one a ground? maybe. I think there is a white and three hots in the channel. How can i check with meter? Ground meter to channel and check each opening? When i find two hots thats what i need for 220v. Will i find a ground in channel? It may be white on top, then ground, then hot, then hot. Or in any order. thanks
     
    Last edited: Nov 27, 2008
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    The hot phases will both read 120 to neutral and ground, but 220 to each other.
     
  5. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    How many hot phases should i expect to find in the 4 wire channel?
     
  6. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    How much voltage does this channel hold? Do they vary in voltage? thanks
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Since it's industrial, it could be a 3-phase buss with a ground.

    Does the buss have a manufacturer name and part number?

    Are their other items also plugged into the buss nearby? Perhaps you can obtain some information from their motor's plates or the like.
     
  8. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    Iam without a name or part number. Some items are 208v single phase. How do i determine if this buss is single only or three phase?
     
  9. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    What is the difference between single phase and three phase?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Sounds to me like it's 3-phase.

    But I'm not a licensed electrician. You need one to advise you.

    In household wiring in the States, you basically have L1, L2, Neutral and earth ground.
    L1 and L2 are taken from opposite ends of a transformer, and Neutral is the center tap of the transformer.
    Neutral is connected to earth ground at the service panel for safety.

    L1 and L2 are 180° out of phase with each other. If you measure from L1 to Neutral or L2 to Neutral, you'll read 120V (nominally) - but from L1 to L2, you'll read 240V.

    With 3-phase, you have L1, L2 and L3. If it's 120v, then any of the phases to Neutral will read 120V, but reading between any two phases will produce 208v. The phases are 120° apart instead of 180°.

    But as I said already, I'm not a licensed electrician. You need one to wire this up properly - and safely.
     
    Last edited: Nov 27, 2008
  11. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    Thankyou, and Happy Thanksgiving, Is there anyone else who can help?
     
  12. explorer12

    Thread Starter New Member

    Nov 27, 2008
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    ok so if the drop is to be made. L1 black hot and L2 red hot leads should be brought down to rectifier to make 208v. Should neutral white and green ground be connected in the buss box or no neutral and just the ground. Remember rectifier only has L1, L2, and ground allocations. In house electrician is available, but not for another week. on vacation. I would not attempt with out him just curious. I want to be prepared ahead of time.
     
  13. floomdoggle

    Senior Member

    Sep 1, 2008
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    Could please you explain what devices you are attempting to hook-up? Instead of the electrical wiring, the device, and its purpose would help.
    Also all 220v wiring in the U.S. is three phase,on the grid, unless modified. My advice to you is to not try connecting anything until you are sure what you are doing.
    The four wires are as Sarge says, two hot, one neutral and one ground.
    Dan
     
  14. floomdoggle

    Senior Member

    Sep 1, 2008
    217
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    I forgot to talk about safety. Make sure if you attempt to wire up any electrical device, the breaker, fuse, or switch is turned off. Then check to make sure there is no power using a continuity checker, meter, or other device rated at the given voltage. And, as always double check and check again to ground, as you will probably be grounded. Do not trust the previous wiring.
    Dan
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Our OP needs a licensed electrican.

    This isn't something that we can help him wire up via the Internet.

    If his company really needs it badly, they can hire another licensed electrician to come in and advise them, give a quote, and hook it up while their onsite electrician is on vacation.

    I've been around electricity/electronics for the last 40 years, but that doesn't make me a licensed electrician.

    There are too many issues at stake here. The safety of the plant (and all that work in it) are involved. This isn't something for amateurs to attempt.

    A licensed electrician will get the job done quickly and safely.
     
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