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  1. Would it also be limited by the size of the...

    Would it also be limited by the size of the service conductors? I see this as a blindspot in the NEC. Consider a 200A service built with #2/0Cu conductors, and suppose you wanted to fully utilize...
  2. More specifically, a customer-owned transformer. ...

    More specifically, a customer-owned transformer. If the utility owns the transformer the conductors would classify as service conductors instead of transformer secondary conductors where 240.21(C)...
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    Neutral generally doesn't count "current...

    Neutral generally doesn't count "current carrying" for purposes of bundling derate factors, but there are essentially two reasons why it would.
    1. It is a mandatory part of the return path of the...
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    For signal and control wiring, the NEC allows you...

    For signal and control wiring, the NEC allows you to fill cable trays to 50% full (in terms of cross sectional area). This is the most ambitious cable tray sizing allowance, of any cable type which...
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    Not necessarily. On feeders and branch...

    Not necessarily.

    On feeders and branch circuits, and anything else behind the main service disconnect, you have control over shutting off the circuit, and would likely do so as standard procedure....
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    The rule on 60C terminals is usually more...

    The rule on 60C terminals is usually more academic than practical. It is a rule that applies in theory, for when equipment/terminals are not specifically listed for any temperature (which is rare). ...
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    90C rated wire does not necessarily mean you need...

    90C rated wire does not necessarily mean you need 90C terminals/equipment. It just means that 60C or 75C rated terminals become the "weak link" in the terminal-wire-terminal assembly. Most...
  8. That's not even remotely close to what the unit...

    That's not even remotely close to what the unit horsepower means at all. It makes no mention of how high the horse lifts the load, and 746 is really the number for the conversion factor of HP to...
  9. Draw out the equilateral triangle, and the "Y"...

    Draw out the equilateral triangle, and the "Y" within it, representing the phase voltages on the complex plane. Put the origin at the center of the "Y". The projection of each leg of the "Y" onto...
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    Taps are governed by 240.21(B). Conductors...

    Taps are governed by 240.21(B). Conductors governed by 240.21(C) are no longer called taps, they are called transformer secondary conductors. The rules are very similar to rules for taps, but the...
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    The reason that works out that way, is as...

    The reason that works out that way, is as follows. When you combine the formula after the f-factor and M-multiplier intermediate steps of the fault current across transformers calculation, you get...
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    Here's how to calculate fault current across a...

    Here's how to calculate fault current across a transformer:
    https://forums.mikeholt.com/showthread.php?t=171709
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    The MPPT range published on the datasheet, is the...

    The MPPT range published on the datasheet, is the range where performance can achieve the published CEC weighted efficiency. It may operate lower than the MPPT range and still seek the array's...
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    That topology is atypical, and is subject to the...

    That topology is atypical, and is subject to the risk that the installer makes an oversight when ordering, and gets it backwards. So you are looking at a somewhat custom transformer, rather than the...
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    NEC2017/690.15 now requires the AC disconnect...

    NEC2017/690.15 now requires the AC disconnect within 10 ft of the inverter, or a remote means to shutoff a more distant disconnect, that can be reached within 10 ft. I think this is overkill in...
  16. In the OP's situation, I would anticipate a small...

    In the OP's situation, I would anticipate a small stub of raceway sleeveing the cable as it exits the building envelope and enters the disconnect enclosure. Would that small stub of raceway also...
  17. It is not the rating of the transformer that...

    It is not the rating of the transformer that governs the sizing of this OCPD, it is the rating of the load connected to its load side. This OCPD has the purpose of protecting the transformer...
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    220.5(B) allows you to round OCPD calculations to...

    220.5(B) allows you to round OCPD calculations to the nearest ampere, if after you apply your safety factors, your number ends up being no greater than 0.5A from the OCPD size you use. That would...
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    A light commercial application will likely be...

    A light commercial application will likely be built with a 120/208V service, and this is the default service voltage unless there's an advantage to having 277/480V. Even larger commercial/industrial...
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    What that section of the NEC is saying, is that...

    What that section of the NEC is saying, is that in certain topologies of transformers, the primary OCPD can effectively protect the secondary conductors too, as if they are a direct extension of the...
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    Erickson is a manufacturer of conduit fittings. ...

    Erickson is a manufacturer of conduit fittings. Their brand was the original manufacturer of the three-piece coupling (aka Erickson coupling), which allows you to independently rotate two pieces of...
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    There are ways you can cut the conduit, without...

    There are ways you can cut the conduit, without re-pulling the cable. Such as using a chain cutter for the conduit and taking extra care to avoid cutting thru the wiring. You will need to plan on...
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    Inside a building, if it is not otherwise inside...

    Inside a building, if it is not otherwise inside a raceway, yes. DC circuits from solar arrays, have to be in metal, in some form or another. This would either mean using metal clad or armored...
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    A 2" nipple of EMT is no longer than the...

    A 2" nipple of EMT is no longer than the back-to-back bodies of the setscrew connectors. I would think the nipple would need to at least have a plain cylindrical section long enough to even fit a...
  25. Thread: 75*C vs 90*C

    by Carultch
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    4,326

    The terminal ampacity would be based on the 75C...

    The terminal ampacity would be based on the 75C column, regardless of how many wires are terminated in the group. It has to do with the whole equipment (i.e. everything inside the factory-assembled...
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