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Thread: How Does Delta High-Leg get 208 to Neutral?

  1. #1
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    How Does Delta High-Leg get 208 to Neutral?

    I'm new to the forum, but am a Journeyman Electrician in Austin, TX. I'm starting to learn about transformers and I've searched the hell out of this site for an explanation that I understand but to no avail...

    My Question:

    How does a Delta High Leg get 240V from leg to leg, but get 208V from the High Leg to Ground, when the other Legs get 120V to Ground?

    I know there's a calculation - 120V x 1.73 = 208...but that equation doesn't explain the HOW I guess. Every diagram I see of Delta transformers make visual sense to me...but how does it happen? If there's 240V from A to B, and B to C...shouldn't all 3 legs have the same voltage to ground?

    I still don't really know why Wye transformers have a ground and Delta's do not so maybe that's where my lack of understanding lies.

    Thanks for any info you have!

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    How good are you with the Pythagorean formula?

    Hypotenuse of triangle = 240V L-L
    Short leg of triangle = 120V L-N
    Missing Leg = ??V High L-N
    Just because you can, doesn't mean you should.

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    Jim nailed it. Here is a picture for more help.

    Name:  Open delta.jpg
Views: 48414
Size:  34.5 KB

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    Wow. Thank you. I love this place lol...
    E=mc2 ...that is all.

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    And BTW, some delta transformer secondaries are grounded, look up "corner grounded delta"
    The advantage of such a system is that three phase power is available for motors, but because one wire is grounded, only 2 pole circuit breakers and switches are needed, rather than 3 pole.

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    Excellent post I must say.. Simple but yet entertaining and engaging.. Keep up the awesome work!

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    Quote Originally Posted by broadgage View Post
    And BTW, some delta transformer secondaries are grounded, look up "corner grounded delta"
    The advantage of such a system is that three phase power is available for motors, but because one wire is grounded, only 2 pole circuit breakers and switches are needed, rather than 3 pole.
    The "delta high leg" system is grounded also otherwise there would be no "high leg" it is just grounded at a different point in the system.

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    Quote Originally Posted by broadgage View Post
    And BTW, some delta transformer secondaries are grounded, look up "corner grounded delta"
    The advantage of such a system is that three phase power is available for motors, but because one wire is grounded, only 2 pole circuit breakers and switches are needed, rather than 3 pole.
    Is it always the "high" leg that gets corner grounded?

    Thanks for the info
    Last edited by teufelhounden91; 06-22-12 at 05:21 PM.
    E=mc2 ...that is all.

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    Quote Originally Posted by sabatini View Post
    Excellent post I must say.. Simple but yet entertaining and engaging.. Keep up the awesome work!
    I agree...I didn't think about the fact that each leg is 60 degrees apart so simple algebra once again solves everything lol. Why did I hate my Algebra teacher again?
    E=mc2 ...that is all.

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    Quote Originally Posted by teufelhounden91 View Post
    Is it always the "high" leg that gets corner grounded?

    Thanks for the info
    No. You won't have a high leg on a corner grounded delta.

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