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Old 09-23-2012, 08:42 AM   #1
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20KW generator connection

Hi All,
Just looking for a nod of approval for my plan in wiring up my 20KW genset.. Please let me know if this all sounds good.. much appreciated!
  • For ATS: I will run 3 copper 3/0 gauge THHN conductors from my meter pan in 2" sched 40 PVC to a 200A Service Entrance ATS. The run is about 8 feet and in a protected area.
  • I need to bond neutral AND ground at that point at the ATS (has 200A breaker) and isolate them in my main load center where they are currently bonded together. I will move the #4 bare stranded ground bonded to two ground rods and plumbing from the main load center to the ATS bonding lug.
  • I will run new #4 bare stranded from ATS bonding lug to Main Load Center ground.
  • The feeder from the ATS to the Load Center (panels are adjacent) will be 3/0 THHN copper in 2" sched 40 PVC.
  • Genset is 20KW and has a 100A breaker. I plan to run 3 individual #3 THHN Copper conductors and a #4 insulated ground.
  • Wiring for GenSet will be buried and run in 1" (for low voltage, factory control harnesses and cat6 ethernet) and 2" (for line voltage, 3-#3's + 3- #12 stranded for block heater) in sched 40 PVC. Distance from panel is approx. 70 feet.
Does this all sound OK? Your input and/or advice is greatly appreciated!


Last edited by raybo; 09-26-2012 at 10:40 AM. Reason: title change
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Old 09-26-2012, 10:40 AM   #2
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just bumping this..


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Old 09-26-2012, 11:26 AM   #3
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Wire size seems alright. I'm a little confused as to what exactly you are doing with what seems like your existing grounding electrode. If you remove your wire from your grounding electrode you have to be careful.

As long as you know what you are doing with an automatic transfer switch and a generator and are following the manufacturers instructions you could be okay. I personally wouldn't advise doing something like this is you aren't qualified.
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Old 09-26-2012, 05:09 PM   #4
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Genset conductors need to rated at 115% of the generator output. #3's are too small.
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Old 09-26-2012, 05:38 PM   #5
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I disagree. A 20 KW is only 83.3 amps on LP and 75 amps on natural.

Also, I read that as a manufacturers responsibility since it says "from the generator terminals to the first OCPD. Which is already built in from the factory.

I know this is going to start something but here goes anyway, since this generator is feeding the entire service then 310.15(B)(6) should apply, so #4 should be ok.
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Old 09-27-2012, 10:41 PM   #6
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The generator will be on LP so yes, ~ 85 amps, so while #4 wire meets requirements, I though I'd just use #3 because of the length of run and because the generator breaker is rated at 100 amps.

Regarding the ground, as I understand it needs to be tied together with the neutral at the ATS, because that now becomes the service entrance. The main panel then becomes a "sub panel" to this and needs to have the ground and neutral isolated - so this changes from the present configuration in the main panel.
This is correct, right?


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