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 Post subject: "... in its Immediate Power Supply"?
PostPosted: Wed Apr 23, 2008 6:16 pm 
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Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Oak Ridge, Tennessee
What do you think qualifies as immediate power supply?

I notice in some programs, for anything below 240V it means the nearest upstream transformer, even if it is a few panels up.

This is in reference to IEEE 1584, p6, where it says, "equipment below 240V need not be considered unless it involves at least one 125kVA or larger low-impedance transformer in its immediate power supply." Immediate is nowhere defined in the standard, and I am not sure I have seen it defined in any other common standards.



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PostPosted: Thu Apr 24, 2008 9:33 am 
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Joined: Thu Jul 19, 2007 7:54 am
Posts: 201
Location: St. Louis, MO
Not sure what the intent was, but I usually cut it off at the first panel, unless the next level is fed by a large breaker / wiring.
I would make this call based on the previous part of the sentence: "...low-impedance transformer..."

Any smaller sized wiring leading to the downstream panels may have enough impedence to qualify, and reduce the hazard significantly.

What the cutoff is, I don't have any idea. I look at them case by case.

I know, not much help. I thought you guys were working on a study standard to clarify this stuff?

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