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Thread: Transformer not used to capacity

  1. #11
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    If I recall, transformers run best when loaded to 80% &+.

  2. #12
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    Quote Originally Posted by sameguy View Post
    If I recall, transformers run best when loaded to 80% &+.
    They do have an optimal efficiency had a specific load. It should be in the specs

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  3. #13
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    Thanks all! I found another thread that describes my situation almost exactly.

    http://forums.mikeholt.com/showthread.php?t=143652

  4. #14
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    Schaltung means wiring or circuit
    Ya0 is the vector group, basically the euro configuration designation

    are you sure it's Ya0 ?

    Y means wye primary
    a = ?? (v?)
    0 no phase shift, 0 deg
    Last edited by Ingenieur; 03-06-18 at 04:42 PM.

  5. #15
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    Quote Originally Posted by DrSparks View Post
    Yup but remember you can round up to the next higher standard ocpd rating if under 800a

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    only on the secondary side.
    Bob

  6. #16
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    Quote Originally Posted by nathanslc View Post

    he insists that the conductors must be sized to the nameplate of the transformer. Call me crazy, but there is nothing that requires me to use 100% of the transformer and I should be able to size my secondary conductors off of the 160 amp breaker, correct?
    Quote Originally Posted by DrSparks View Post
    You do not have to size the wiring to the maximum capacity of the Transformer. You size the wiring according to the ocpd and load requirements

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    True for <600 volt transformers, but note 215.2(B)(1) requires feeder to be greater than or equal to namplate capacity. OP, You might point him toward 215.2(A) which has no such requirement.
    Last edited by electrofelon; 03-06-18 at 07:28 PM.
    Ethan Brush - East West Electric. NY, WA. MA

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  7. #17
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    Quote Originally Posted by DrSparks View Post
    Yup but remember you can round up to the next higher standard ocpd rating if under 800a

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    Actually, I dont see that there is an 800 amp limit for use of the next size up rule for transformer protection.

    Quote Originally Posted by petersonra View Post
    only on the secondary side.
    I can use next size up if I am using 125% primary protection, but not if I am using 250% primary (with secondary protection).
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #18
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    "Schaltung" just means "circuit", Ya0 is the transformer "vector group" designation, an IEC standard numbering system we don't use here (it comes from the very organized Germans).
    Ya0 vector group describes the relationship and configuration of the primary and secondary.
    "Y" means the primary is a wye (star) configuration,
    "a" means secondary is an autotransformer (so is the same as the primary, wye)
    "0" means the phase displacement between primary and secondary is zero degrees,

    The 0 seems obvious if it's an autotransformer, but those Germans like to be consistent...

    So you have a Y-Y autotransformer, there is probably no "neutral" connection terminal for it either, but if there is, it's only going to be one.
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  9. #19
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    if it has a neutral it will have an N or n (prim/sec) after the winding designation

    eg Dyn0

  10. #20
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    Quote Originally Posted by Ingenieur View Post
    if it has a neutral it will have an N or n (prim/sec) after the winding designation

    eg Dyn0
    Yep, you are right. So there will be no Neutral connection on that transformer, and as an autotransformer, I don't see why it would anyway.

    Back to the original question about capacity, there is nothing saying you MUST size protective devices for anything MORE than the intended load. It says you CAN, but not MUST. the NEC only says it MUST NOT be any larger than a certain value. So if you are only going to use 160A off of that transformer, you can use a 160A breaker if you want to, so long as that transformer is capable of 160A or more.
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