Conductor sizing, branching and disconnects on a mobile HVACR+generator system

[FAZERS]

Hi,

I have 3 HVACR code questions, one regarding feeder conductors, one regarding a transformer branch circuit and another involving a disconnect.

I am helping design a mobile, trailered refrigeration system powered by a 295KVA, 480Y/277 prime duty generator with a nameplate current rating of 355A that is located on the same deck. In the compressor control room where the ICP is located, I found what I believe are the most relevant articles, totaling 3, that describe and affect the feeder conductor requirements from the generator output panel to the ICP feeder.

Per 2023 NFPA 70, article 409.3, "Other Articles" from 409/Industrial Control Panels:

"In addition to the requirements of this article, industrial control panels that contain branch circuits for specific loads or components, or are for control of specific types of equipment addressed in other articles of this Code, shall be constructed and installed in accordance with the applicable requirements from those articles."

Per 2023 NFPA 70, article 409.20, "Conductor -- Minimum Size and Ampacity," from 409/Industrial Control Panels:

"The size of the industrial control panel supply conductor shall have an ampacity not less than 125% of the full-load current rating of all heating loads plus 125 percent of the full-load current rating of all heating loads plus 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all other connected motors and apparatus based on their duty cycle that may be in operation at the same time."

Per 2023 NFPA 70, article 445.13(A), "Ampacity of Conductors" from 445/Generators:

"The ampacity of the conductors from the generator output terminals to the first distribution device(s) containing overcurrent protection shall not be less than 115 percent of the nameplate current rating of the generator. It shall be permitted to size the neutral conductors in accordance with 220.61. Conductors that must carry ground-fault currents shall not be smaller than required by 250.30(A).. ..Exception: Where the design and operation of the generator prevent overloading, the ampacity of the conductors shall not be less than 100 percent of the nameplate current rating of the generator."

Question 1: Do I just reference the most conservative guidance mentioned from these 3 articles, thus the requirements of 409 in this case trumping 445? I suggest this due to the first article verbiage "In addition to.."

Question 2:
I don't mention article 440 much above because it is more focused on branch protection and motor configuration of those branches. All of my motor-compressors are single unit branches each with either a listed Type E/F CMC or a listed combination of Restricted starter/UL489 MCCBs. None of these branches use a neutral conductor from the generator. I do, however, have a couple needs for independent 120VAC:

1. Safety systems like diagnostic modules bolted to the compressors
2. Heaters for the compressors that need to run for a while prior to compression
3. Solenoids for the unloaders for each compressor
4. For actual control, like relays and switching power supplies to acquire 24VDC for PLCs, process transducers and other relays

...so I decided to start with a dry-type (TF) control transformer, 2KVA, and would like to try and install it inside the control panel. Is this a common practice from a branching perspective? I am not sure how to proceed with an OCPD for this branch because I fear the transformer's inrush may nuisance trip it. I am also not that knowledgeable on transformers.

Question 3: How does the generator's panel breaker factor in here, specifically, do I still need an OCPD or disconnect between the feeder of my ICP and the transformer branch? I read something in NEC about series OCPDs being unadvisable, but I can't locate the article anymore to figure out the exact context.


Thanks!