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  1. Replies
    4$$
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    249

    I think I agree with Ron, although the code isn't...

    I think I agree with Ron, although the code isn't as clear as I expected it to be, and even the handbook doesn't help much.

    I think you would be correct if the emergency lighting was unit...
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    12$$
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    695

    I know nothing is a sure thing if lawyers get...

    I know nothing is a sure thing if lawyers get involved. But if the NEC doesn't require NM calcs; I don't see other engineers doing the calcs; and even the handbook suggests its not required then...
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    12$$
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    695

    That's pretty much seems to agree with the...

    That's pretty much seems to agree with the handbook info.



    That looks like it comes straight from the ampacity tables with (7) sets of 500KCM being good for 7 * 380 amps = 2660 amps. But why...
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    12$$
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    695

    Neher Mcgrath and duct bank derating

    I've almost always determined cable ampacity straight from table 310.15(B)16 - the standard 3 conductors in a conduit table. Even for underground runs with more than one conduit (aka - a duct bank)....
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    30$$
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    1,422

    You may also want to consider a switched mode...

    You may also want to consider a switched mode power supply. They are usually more complex, and normally include an inductor, but they are typically more efficient and they reduce the input current...
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    11$$
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    732

    Agreed - it won't be pure water. But I'm not...

    Agreed - it won't be pure water.

    But I'm not sure what that means for the original question. Its probably common to put these pumps in pits, conductive water or not.
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    11$$
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    732

    Pool water is treated with chlorine, which makes...

    Pool water is treated with chlorine, which makes it highly conductive.

    The way I understand it, some of the chlorine atoms (or maybe all of the chlorine atoms) looses an electron and become...
  8. Replies
    30$$
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    1,422

    Can you determine the peak diode current? That's...

    Can you determine the peak diode current? That's one very important parameter for diode rectifier design. Both at stead state, and also when the power is first applied and the caps. are completely...
  9. Replies
    30$$
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    1,422

    How are you getting from a 3 phase input to a...

    How are you getting from a 3 phase input to a single phase output?

    Also, have you thought about the harmonic currents this will induce into the AC supply?



    Before I went too far down the...
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    16$$
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    839

    I'm not sure, but I think the transformer...

    I'm not sure, but I think the transformer nameplate will explain that in detail. Here is the nameplate from a different xformer that has 7 taps;

    23322

    Looking at a couple of different...
  11. Replies
    16$$
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    839

    Sounds right. I tried googling transformer taps...

    Sounds right. I tried googling transformer taps earlier and came up empty. But a search for "changing taps on a transformer, was more productive, and I found this;
    ...
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    16$$
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    839

    Yes, not that you say that I would agree - 6...

    Yes, not that you say that I would agree - 6 total at 2.5% each, with 2 up and 4 down. That makes more sense

    Now, does the 4- mean it lowers the secondary voltage, or its for a lower primary...
  13. Thread: CAD issue

    by steve66
    Replies
    5$$
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    463

    Sure you can? Not sure if you mean "move the pdf...

    Sure you can? Not sure if you mean "move the pdf around in the drawing" or if you mean "move the file location"?

    But you can do either. If you move the file location, you just have to use a...
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    16$$
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    839

    23315

    23315
  15. Replies
    16$$
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    839

    Transformer Taps

    Standard dry type 300KVA 480V delta to 208V wye transformer.

    Shop drawings say "Taps 6 - 2.5% 2+4- Taps"

    I would assume these are secondary taps, and that means there are six taps at -2.5%? ...
  16. Replies
    20$$
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    1,054

    Interesting and educational. From the...

    Interesting and educational.

    From the curves, it looks like the general idea is that if the breaker is set at 40 amps, then it would never trip at anything below 40 amps, but it would trip as...
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    20$$
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    992

    It also looks like one of the breakers on the...

    It also looks like one of the breakers on the line side of the transformer may trip on transformer inrush current.
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    55$$
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    2,205

    Looking at the Square D catalog, you can spec....

    Looking at the Square D catalog, you can spec. thermal magnetic for up to 400 amp breakers with the Q4 and LA breakers;
    ...
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    55$$
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    2,205

    No, probably a separate magnetic trip for each...

    No, probably a separate magnetic trip for each phase.
  20. Replies
    4$$
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    520

    Back up a second. Why do you have to have...

    Back up a second. Why do you have to have anything outside?

    230.70 doesn't require a disconnecting means to be outside. Outside is just one of 2 options listed in 230.70 A1.
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    28$$
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    1,329

    But there are restrictions - big equipment goes...

    But there are restrictions - big equipment goes on the equipment branch (only fractional horsepower motors are allowed on the critical branch), and only loads required for emergency use are allowed...
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    3$$
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    417

    Is it a health care facility? That could...

    Is it a health care facility? That could complicate things a bit since hospital generators are given some relief from the load calculations required by 220.

    Otherwise, the only requirement would...
  23. Replies
    28$$
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    1,329

    I've wondered about that a lot also. Only the...

    I've wondered about that a lot also. Only the LS branch has to comply with the stricter requirements in 700. So its obviously considered more important.



    Hospitals are usually designed with...
  24. Replies
    14$$
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    763

    I'm not 100% sure, but I always thought the 6x...

    I'm not 100% sure, but I always thought the 6x rated current or locked rotor current rating was required for the additional service disconnecting means permitted by 695.4(B)(1)(a).

    The other specs...
  25. Thank you. I was a little concerned that the...

    Thank you. I was a little concerned that the "alternate source" mentioned in 517.31 would not include a panel or switchboard downstream of the generator itself.

    But the 99 quote seems to say I...
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