22kw Generator wire sizing

Reply

  #1  
Old 12-28-18, 12:33 PM
J
Member
Thread Starter
Join Date: Dec 2018
Location: USA
Posts: 2
Received 0 Votes on 0 Posts
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.
 
Sponsored Links
  #2  
Old 12-28-18, 04:05 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 57,651
Received 907 Votes on 847 Posts
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.
 
  #3  
Old 12-28-18, 06:55 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 10,599
Received 71 Votes on 62 Posts
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.
 
  #4  
Old 12-29-18, 02:59 PM
J
Member
Thread Starter
Join Date: Dec 2018
Location: USA
Posts: 2
Received 0 Votes on 0 Posts
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!
 
  #5  
Old 07-31-20, 08:31 AM
E
Member
Join Date: Jul 2020
Posts: 1
Received 0 Votes on 0 Posts
130' Wire Run

I have the same situation but with a 130' wire run. I was thinking AWG 1 for the three power lines, AWG 6 for the ground and AWG 16 for the six control wires. Are any of these overkill?
 
  #6  
Old 07-31-20, 09:06 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 57,651
Received 907 Votes on 847 Posts
Welcome to the forums.

There is code minimum and then there is real world.
I would agree with your choice of wire sizes..... although even #2 copper would be good.

I have issues with Generac's handling of low voltage wiring. I believe they illustrate running the high voltage and control cables in one conduit. We always run the control wiring in a separate 3/4" conduit.
 
CasualJoe voted this post useful.
  #7  
Old 08-01-20, 05:00 AM
T
Member
Join Date: Oct 2005
Location: USA
Posts: 1,575
Received 29 Votes on 28 Posts
The safety engineering with LV accessible control wiring is to have it "double insulated" away from hazardous wiring. Thus, one can be certain that, for instance, 24V thermostat wiring will not be dangerous to touch. It is quite typical to work on a 'stat replacement, with a live system, for example.
But, when the LV wiring is classified as "not accessible", likely in the standby genset case, the rules change. In fact, in the Generac case, some of the control wiring contain line voltage and some contain LV. If the LV wiring is routed and contained within a touch proof enclosure, requiring tools for entry, then it should be permissible to run them with line conductors.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: