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Thread: 3 phase questions

  1. #16
    My new building has 240v corner tapped delta. I prefer it over 208Y, but I would rather have 480Y service.

    With 240v delta, just install a couple sub panels for your 120/240 single phase needs and keep all 3 phase loads in same panels. I need to set a couple transformers, one to get 480v and one to get 600v.

  2. #17
    Quote Originally Posted by Sam Beagle View Post
    So I bought an old elks lodge which I’m turning into my new shop. I recently found out the building has 3 phase power in which I’ve been paying a monthly fee to have. How can I find out what is 3 phase and where’s it is coming I
    The fact you have to pay a fee for your 3 phase service makes me think it's tapped from lines feeding mostly residential services. If so that means you have the option to keep the 3 phase service or change it over to single phase and drop the fee.

    As far as what is 3 phase, I'm guessing you mean what in the building requires 3 phase to feed it. First thing I would do is look at the panel and see how many 3 pole breakers there are. If a panel directory exists and it is accurate and updated, that will tell you what the 3 phase loads are. I'm taking it you want to reuse as many of the existing feeds there are to power up your tools.

    You asked "where’s it is coming I". Do you mean where is the feed outside?
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  3. #18
    Quote Originally Posted by Darcy Warner View Post
    My new building has 240v corner tapped delta. I prefer it over 208Y, but I would rather have 480Y service.

    With 240v delta, just install a couple sub panels for your 120/240 single phase needs and keep all 3 phase loads in same panels. I need to set a couple transformers, one to get 480v and one to get 600v.
    I've got a 40kva step up transformer I'd sell/trade. You're not going to be able to run anything huge, but I think that's in the ballpark of 45amps of 480

  4. #19
    Quote Originally Posted by Martin Wasner View Post
    I've got a 40kva step up transformer I'd sell/trade. You're not going to be able to run anything huge, but I think that's in the ballpark of 45amps of 480
    That may take care of section of machines. There is a 112.5 kva in there I am going to move, I have another 112.5kva I am moving with me.

  5. #20
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    Sam:

    Out of curiousity, what does your utility charge you as the monthly fee to have 3-phase electricity? I took a different route, as I really hate dealing with Dork Energy down here.
    - After I ask a stranger if I can pet their dog and they say yes, I like to respond, "I'll keep that in mind" and walk off
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  6. #21
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    Quote Originally Posted by Darcy Warner View Post
    My new building has 240v corner tapped delta. I prefer it over 208Y, but I would rather have 480Y service.

    With 240v delta, just install a couple sub panels for your 120/240 single phase needs and keep all 3 phase loads in same panels. I need to set a couple transformers, one to get 480v and one to get 600v.
    i have a Canadian Wadkin with a 600v 3 phase motor. Is it cheaper / better to rewind motor to 240v or buy a step up transformer (which don’t seem very common from some prelim sesrches).

    Thx

    jon

  7. #22
    Quote Originally Posted by Martin Wasner View Post
    I've got a 40kva step up transformer I'd sell/trade. You're not going to be able to run anything huge, but I think that's in the ballpark of 45amps of 480

    A transformer by code can only be used to step up the voltage if the manufacturer says it can be done with that transformer, that requirement was added to the 2014 NEC. 450.11(B)

  8. #23
    Quote Originally Posted by Rollie Meyers View Post
    A transformer by code can only be used to step up the voltage if the manufacturer says it can be done with that transformer, that requirement was added to the 2014 NEC. 450.11(B)
    Manufacturer of what? The transformer, or what is being plugged into it?

  9. #24
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    Quote Originally Posted by Martin Wasner View Post
    Manufacturer of what? The transformer, or what is being plugged into it?
    The transformer manufacturer. We have the same rule in the CEC. It was adopted in the last release, or maybe the one before. Functionally, a transformer will work as a step up or step down, depending on which windings you connect to the line. But inspection authorities require that the line be connected to what the label identifies as the primary windings & the load to the secondary windings. The only explanation I've been able to find for this somewhat bizarre rule is that the transformer was tested & approved by the certification agency as per the label, and connecting it in reverse is an off label application therefore illegal.

    I am a believer in sticking to the code and the vast majority of its requirements are justified. But unless there is something I don't know, I think this one is a pretty silly. At some point, rational thought and logic have to be allowed to be used.

  10. #25
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    Frank, although the transformer will indeed work backwards, a standard Delta primary, Wye secondary transformer when connected backwards yields a non ground referenced secondary which can be dangerous.

    Regards, Rod

  11. #26
    Quote Originally Posted by Rod Sheridan View Post
    Frank, although the transformer will indeed work backwards, a standard Delta primary, Wye secondary transformer when connected backwards yields a non ground referenced secondary which can be dangerous.

    Regards, Rod
    Three phase power is certainly not my area of expertise, but wouldn't any delta connected three phase power have no ground reference? How would you connect a ground reference with a delta connection?

    Mike

    [And if you have the secondary of a transformer and that secondary has no ground, current can't flow between a line and ground. The danger, to my mind, is that a ground occurs on one line (which no one notices) and that provides a path for current to flow from one of the other lines (perhaps through a person) to ground. But I'm not at all an expert on power systems.]
    Last edited by Mike Henderson; 02-17-2019 at 7:41 PM.
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  12. #27
    It is a step up transformer.

    I got it with a piece of equipment where the guy didn't have have 480, and the machine couldn't be switched over to 208

  13. #28
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    Of course the Op may be on the other side of the world. This could make shipping a heavy transformer expensive. I do not think he is in Zimbabwe is he?
    Bill D
    USA

  14. #29
    Quote Originally Posted by Rod Sheridan View Post
    Frank, although the transformer will indeed work backwards, a standard Delta primary, Wye secondary transformer when connected backwards yields a non ground referenced secondary which can be dangerous.

    Regards, Rod
    Is this dangerous because of possible short transmission connected a to common Ground Backfeeding?

    Rod, so what is your position on autotransformers. They can step up or step down. The manufacture can state it either way.

    With a ground fault breaker adequately in place, Wouldn’t this alleviate stepping up using a auto transformer ground issue?

    I’m not a EE but this is how my system has been set up.

    [I’m fully aware of the distribution “clause” with anything more than 150 V to ground permanent hook up.]

    Six of my machines have autotransformers built in. 2 of my machines use step up auto transformers before.

    One has two transformers, one stepping up to 600 V, and one stepping down to 120 V from 240 V three-phase.
    Last edited by Matt Mattingley; 02-18-2019 at 1:35 AM.

  15. #30
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    Quote Originally Posted by Mike Henderson View Post
    Three phase power is certainly not my area of expertise, but wouldn't any delta connected three phase power have no ground reference? How would you connect a ground reference with a delta connection?

    Mike

    [And if you have the secondary of a transformer and that secondary has no ground, current can't flow between a line and ground. The danger, to my mind, is that a ground occurs on one line (which no one notices) and that provides a path for current to flow from one of the other lines (perhaps through a person) to ground. But I'm not at all an expert on power systems.]
    Hi Mike, you’re correct.

    True ungrounded delta systems are very rare, I’ve worked in large places with them, and they had voltage monitoring protection to determine if one phase was grounded through a fault.

    In a 600/347 system the line to ground voltage would rise to 600 from 347 on the ungrounded phases, this could reduce insulation life and increase shock hazard for personnel.

    Many systems that people think are delta, are simply grounded wye systems where the neutral isn’t carried beyond the secondary, which is solidly grounded or resistivels or reactively grounded.

    The other issue with a non grounded system is that voltages can rise well beyond rated voltage to ground via transients, very risky.

    This is why you need either an auto-transformer or a delta secondary so you can preserve the ground reference or establish a new one by grounding the neutral point.

    Regards, Rod

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