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Thread: Bonding XO when not using a neutral conductor

  1. #11
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    Thanks for all the input guys, I really appreciate it. Sorry I wasn't able to reply sooner. I made a mistake in my original post, the transformer was indeed 480/208, not 480/240. There are a total of three- one 480/208 delta/wye and two 480/240 delta/delta --- I got them mixed up while typing.

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    This is how we ended up wiring the transformer, with the line from the panel coming in on the right, and the load out the ECB on the left. We have a jumper from the X0 to the ground bus bar, and the fourth wire from there goes out to building steel.

    (spec on this job is for wire to be Red Orange Black regardless of voltage)

  2. #12
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    Quote Originally Posted by Mike_J_H View Post
    ...This is how we ended up wiring the transformer, with the line from the panel coming in on the right, and the load out the ECB on the left. We have a jumper from the X0 to the ground bus bar, and the fourth wire from there goes out to building steel.

    (spec on this job is for wire to be Red Orange Black regardless of voltage)
    I have no personal argument with that spec, but how did you comply with 215.12(C)
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

  3. #13
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    Agreed on the 215.12C, feeders should have different colors or tagging to differentiate the different voltage systems and be posted on equipment, for personnel to be able to tell the difference of each nominal voltage system. Since you have three nominal voltage systems, you should have three different color or tagging arrangements.

    On the delta to delta transformers, does the low voltage side have a center tap XO? Did you bond it the same way as the Y transformer secondary?

    Is your bonding jumper from the XO terminal sized in compliance with 250.102 (C) (1) ?

  4. #14
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    Methinks confusion exists around XO as a bond or as a component of an SDS .

    I just went through this with an install, not mine, where i could not get a reading from any hot to ground......



    Realizing no reading equates to not grounded, led me to the manufacturer.

    I had not seen an XO and was confused, but in fact one did exist under the coils, not out front with the rest of the terminations

    simply bonding it allowed for any given secondary hot to read to ground.

    you wouldn't believe the generation of sparks who had introduced all manner of extraneous and redundant EGC's downstream ,in a futile effort to ground the secondary circuitry, all of it nonfunctional as a path to OCPD performance.

    two feet of CU cured it all


    ~RJ~

  5. #15
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    Quote Originally Posted by MTW View Post
    Agreed on the 215.12C, feeders should have different colors or tagging to differentiate the different voltage systems and be posted on equipment, for personnel to be able to tell the difference of each nominal voltage system. Since you have three nominal voltage systems, you should have three different color or tagging arrangements.

    On the delta to delta transformers, does the low voltage side have a center tap XO? Did you bond it the same way as the Y transformer secondary?

    Is your bonding jumper from the XO terminal sized in compliance with 250.102 (C) (1) ?
    I agree 100% on phase colours, but this facility has their way of doing things and we're forced to comply if we want to keep working there. Every piece of equipment we hook up has engraved labels telling voltage (input/output in the case of transformers), what it feeds, and where it is fed from.

    One delta to delta transformer has an X4 and the other an X6, center tapped between A & B and between C & A (I believe). For both: voltage was 240V between each phase, 212V highleg to ground, and 120V other two legs to ground. For both, X4/X6 are bonded to building steel and bonded to a ground bus on the transformer case.

    Bonding jumpers were oversized to 2AWG on all three transformers.

  6. #16
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    the paint under that ground bar doesn't look very conductive. was that in there from the factory?

  7. #17
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    Quote Originally Posted by Kinexis View Post
    the paint under that ground bar doesn't look very conductive. was that in there from the factory?
    That's a factory bar I don't understand why factory EGC terminals do not have to remove the paint but field installed ones do.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  8. #18
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    Quote Originally Posted by infinity View Post
    That's a factory bar I don't understand why factory EGC terminals do not have to remove the paint but field installed ones do.

    it's tested by a recognized laboratory, either way i would remove the paint and use that grease you used on the transformer connections.

  9. #19
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    Quote Originally Posted by Kinexis View Post
    it's tested by a recognized laboratory, either way i would remove the paint and use that grease you used on the transformer connections.
    Even field installed bars sometimes get attaced to holes already tested and intended to accept the bar or lug. I never remove paint on those.

    They aren't any better or worse then many loadcenter "bonding screws". Seen a few of those fail because they maybe weren't properly tightened when installed - they they fail when called upon to carry fault current.
    I live for today, I'm just a day behind.

  10. #20
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    Quote Originally Posted by Kinexis View Post
    it's tested by a recognized laboratory, either way i would remove the paint and use that grease you used on the transformer connections.
    I agree that is the reason, I would just use the bar as is from the manufacturer why bother with the extra work?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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