ATS Parallel Conductor Sets

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dvcraven0522!

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St. Louis
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Electrical Design
Good Morning.

I have a scenario where I have a project with 100% generator back-up. The generator will be located near the pad mounted transformer. The main service equipment CT enclosure, ATS, and MDP are located approximately 375' from the generator. I have sized the feeders to the ATS for voltage drop as shown in the attached PDF file highlighted in yellow.

My question is are the feeders from the ATS to the MDP (highlighted in green) required to the same although the distance to the ATS and MDP are relatively close to each other.
 

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IMO,
1. I would relocated the generator close to bldg. which would save some cost on cables/duct if possible.
2. Since the ATS as SE, It would show the CB on Normal side, and I would ground N or grounded conductor at the ATS.
3. I wouldn't run EGC/SSBJ from Xfromer and Generator to ATS (assume they are outdoor).
4. I would put SPD at the ATS. My last experience that the surge/lightning strike took out my ATS while everything okie bc the SPD was put at the MDP.
 
The size of the phase conductors do not need to be the same. However, see note #5 below regarding EGC sizing.

I can't help but comment, but a couple of notes that may or may not have been hinted by previous posters:
  1. Why are you using a 4P ATS? This does not appear to be an application where you need to switch the neutral as it is 208V and not 480V.
  2. Your ATS is your service entrance so the MBJ/GEC connections would be occurring there and not at "MDP" as you show it. As noted in post #5, there should be a 1200A circuit breaker on the normal side of the ATS.
  3. Service conductors do not need a "ground" conductor (ie, from the T1 utility transformer all the way to your ATS). The three phases and a neutral is all you need. The neutral is the grounded conductor; an EGC or SSBJ is not required, nor is there anywhere to land them...
  4. You will however need an EGC from your generator main circuit breaker to your ATS as it is a feeder. Make sure to increase EGC size per 250.122(B) (NEC 2017) as it appears you are increasing the EGC size due to voltage drop.
  5. To err on the side of caution, I would also upsize the EGC between the "load" terminal of the ATS to your MDP to match the EGC size of your generator feeder. I'm interested to see what people think of this one, but when the generator is running, I would imagine the EGC between the generator circuit breaker and MDP needs to be the same as that outdoor generator feeder portion still has upsized conductors.
 
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