22kw Generator wire sizing

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Old 12-28-18, 01:33 PM
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22kw Generator wire sizing

Hi all, sorry for starting off with asking a question but I'm hoping the community can help me from making a potentially expensive mistake. I recently purchased a 22kw Generac Guardian series air cooled standby generator. It will be running off propane and is located approximately 75' from my home's service entrance. The generator came with a service entrance rated automatic transfer switch. The generator and transfer switch are rated in the 75C column according to their labeling, and the generator has a 100 amp circuit breaker and a max output of 91.7 amps when running on LPG. Looking at both voltage drop calculations and the 75C column of 310.15 it would appear that #3 Copper would be sufficient for my purposes. #3 can carry 100 amps in the 75C column and voltage drop for an 85' run (added a few feet on for bends and whatnot) is 2.79%, just shy of the max 3%. Generac also conveniently sells installation cable for their 17-22kw generators that contains 3x #3awg + ground, + the 6 control cables in #18awg. They say that cabling is sufficient for installs of up to 113' away. With all that said I was feeling pretty good about buying that convenient all in 1 cable until I started reading here and other places where people were saying the under no circumstances can #3 carry 100amps. I've read some people saying you have to go up to #2 and others saying you have to go as big as 2/0! My plan was to order the cable and do my own trenching and conduit install and then have a licensed electrician come and help me with the final hook ups. I don't want to buy this cable if it won't end up passing an inspection after the fact. Opinions? I l live in an unincorporated area of King County in Washington state if that makes a difference. Thanks in advance for the help.
 
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Old 12-28-18, 05:05 PM
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Welcome to the forums.

You will be using a 200A service rated ATS ........ correct ?
That ATS becomes the main panel which means all grounds and neutrals must be separated at what is now your main panel. Your main panel will become a sub panel. You will need to install ground bars. If your water pipe ground goes to your main panel..... it will need to be moved or extended to the ATS. The splice must be done with permanent crimp.

I see no reason to not use #3 copper. It is rated to handle that load.
 
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Old 12-28-18, 07:55 PM
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I saw nowhere that you ever mentioned the size of your current electric service, but if you have a 200 amp service I agree completely with PJ.


I started reading here and other places where people were saying the under no circumstances can #3 carry 100amps.

Totally bogus, #3 copper is what you need for 100 amps. As a side note, only #4 copper is required for a 100 amp service. Regardless, #3s are what I would use.


I've read some people saying you have to go up to #2 and others saying you have to go as big as 2/0!

Those folks obviously do not have a clue.
 
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Old 12-29-18, 03:59 PM
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Thank you both for the quick replies. Yes, 200 amp service to the house and a 200 amp ATS. I figured as much but I didn't want to order the wire (which can't be returned once cut) and then end up making a $500 mistake. Thanks for the assistance!
 
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