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  1. #1

    3 phase to 120v problem

    I'am putting AC in a auto body shop. The shop has a 3 phase breaker box and I ran 14 wire to the air handlers from 15 amp breakers. I have voltage at the outlet and switch but nothing works. We thought the box wasn't grounded properly so we put a grounding rod in but it still doesn't work.

  2. #2
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    I have a guess but are you a HVAC-R technician or electrician?

  3. #3
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    What exactly are you doing? What is the nameplate electrical data. From what you wrote I really think you should call a HVAC company just like us when we dent our service trucks, we go right to you to get them fixed up. You guys do your jobs very well and so do we.
    ckartson
    I didn't write the book I just read it!

  4. #4
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    Quote Originally Posted by rjshantz View Post
    I'am putting AC in a auto body shop. The shop has a 3 phase breaker box and I ran 14 wire to the air handlers from 15 amp breakers. I have voltage at the outlet and switch but nothing works. We thought the box wasn't grounded properly so we put a grounding rod in but it still doesn't work.
    Which is 100% predictable.

    I would need more information to help you. Also, if you are an HVAC Pro, apply for Pro membership by clicking on the link in the bottom portion of this post.

    In the Pro section, we discuss technical issues in greater detail. we don't do that in the "open" areas.

    Ground rods are for lightning protection.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  5. #5
    Sorry about the lack of info I've never posted before. I am an HVAC tech who is working in an auto body shop. Being more familiar with light residential applications of heating and cooling I don't have much experiance with three phase electrical systems. My boss who is running the jobs has worked with three phase before but never had this problem.

  6. #6
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    I can tell you this: it is not a ground rod problem.

    It would not be a ground rod problem in ANY application.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  7. #7
    The shop has an old 3 phase delta service. The transformer on the poll looks like its 100 years old. I understand that were probably having trouble with the neutral conductor I'm just not sure what to do about it.

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    Moved to AOP forum.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
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    Quote Originally Posted by rjshantz View Post
    The shop has an old 3 phase delta service. The transformer on the poll looks like its 100 years old. I understand that were probably having trouble with the neutral conductor I'm just not sure what to do about it.

    This is when you call in an electrician who can determine if your neutral problem is at the transformer, the service drop, the meter can, or the feeders to the panel.

    I can't remember the last time I saw a delta feed coming from a single can transformer. The norm is a trio of transformers, connected in the delta configuration. Most three phase has a Wye secondary, and the electrician can quickly determine if this is the case.

    You have done all you can do with your own skillset. Now, call in an electrical pro.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  10. #10
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    timebuilder- You can get 3 - phase from 2 transformers, it's called an open delta. One of the two transformers will be a bit larger then the other. the neutral is center tapped on one transformer causing the voltages to read in three phase 230 l1 - l2, 230, l2- l3, 230 l3- l1. Draw a 60* angle on a piece of paper. The three points are the line terminations. On the center of the base draw a line coming down (perpendicular) to the base this is the neutral. you have 120 volts from either of the base points to neutral and 208 volts to the riser angle line connection. rjshantz Did you check to verify that you have true 3-phase power to the unit. I have had several accounts that actually had 3-phase on the pole, but abandoned the third leg in the breaker panel. Makes no sense, but it happens. If your not sure call an qualified electrician. If this is a body shop, they have a large air compressor for tools and painting, is it a 3-phase motor ? -GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  11. #11
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    Quote Originally Posted by ga1279 View Post
    timebuilder- You can get 3 - phase from 2 transformers, it's called an open delta. One of the two transformers will be a bit larger then the other. the neutral is center tapped on one transformer causing the voltages to read in three phase 230 l1 - l2, 230, l2- l3, 230 l3- l1. Draw a 60* angle on a piece of paper. The three points are the line terminations. On the center of the base draw a line coming down (perpendicular) to the base this is the neutral. you have 120 volts from either of the base points to neutral and 208 volts to the riser angle line connection. rjshantz Did you check to verify that you have true 3-phase power to the unit. I have had several accounts that actually had 3-phase on the pole, but abandoned the third leg in the breaker panel. Makes no sense, but it happens. If your not sure call an qualified electrician. If this is a body shop, they have a large air compressor for tools and painting, is it a 3-phase motor ? -GEO
    Correct.

    He said "transformer."

    I said "the norm is a trio of transformers."

    This is how three phase is derived using the two transformers you described. Sometimes called "red leg," the NEC requires that the B phase be marked with an orange marking, to indicate its higher voltage value to the grounded (neutral) conductor.


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    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  12. #12
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    timebuilder - please note I did not respond to this post just to get into a pi$$ing contest. A general question was asked and answered. If I misread the quote about the transformer [s] then shame on me. odds are he is looking at a residential single phase transformer. That is why I gave him the suggestion to look at his air compressor. It has to be pretty large to handle the needs of a body shop, so it MIGHT be 3-phase. You and I both know if you connect a 208-230 volt 3-phase unit to an ACTIVE 3-phase 208-230 volt power supply it should run. The neutral is oblivious. As this is a new guest I am not going to go into switchgear troubleshooting to an inexperienced (as far as I know) guest. We are both skilled at the things we do and shouldn't try arguing on a posted suggestion. -GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  13. #13
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    Quote Originally Posted by rjshantz View Post
    I'am putting AC in a auto body shop. The shop has a 3 phase breaker box and I ran 14 wire to the air handlers from 15 amp breakers. I have voltage at the outlet and switch but nothing works. We thought the box wasn't grounded properly so we put a grounding rod in but it still doesn't work.
    From the thread title, he is looking to provide 120 volts from a three phase panel.

    If he can't determine if there is a three phase panel, that is all the more reason to call an electrician.

    No pi$$ing involved.
    Last edited by timebuilder; 08-18-2013 at 02:34 PM.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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