100A Garage Loft Sub Panel Questions


  #1  
Old 11-28-22, 08:14 AM
F
Member
Thread Starter
Join Date: Dec 2005
Location: Virginia
Posts: 266
Received 1 Upvote on 1 Post
100A Garage Loft Sub Panel Questions

New construction garage with loft, sub-panel to be ~25ft from the garage level main panel. I probably don't need 100A but prefer at least 6 circuits and haven't found a Homeline that would work other then the one noted below.
Square D Homeline 100-Amp 8-Space sub-panel in loft of new detached garage. The sub-panel will be fed by the existing 200A panel in garage which has its own separate service/meter (not from house). Ive read that 100A sub requires #4 copper or #2 aluminum. I cant seem to locate #4 copper or Al in SER sheath local but I can get Southwire-2-2-2-4-Black-Stranded-Al-MHF by the foot.
Can I run the 2-2-2-4 shown from the main through drilled holes in the sill/joists/studs like a typical run or will it require conduit?
Any other suggestions is appreciated.
Thanks. FF
 

Last edited by FairwayFatty; 11-28-22 at 10:11 AM.
  #2  
Old 11-28-22, 11:17 AM
C
Member
Join Date: Jul 2009
Location: SE Iowa
Posts: 148
Received 10 Upvotes on 9 Posts
Are you after 100A for the subpanel due to the future expected loads? Or just trying to size a panel with enough spaces?

If you are just after a decent quantity of single pole spaces, you can use pretty much anything for a subpanel. You could even put in a 200A main 42 space panel if you want, and feed it with a 40A feed. I just don't want you to think that just because the label on the box says 100A that you MUST feed it at that rating. The breaker in the main panel feeding the sub is what will drive the conductor size to use.
 
CasualJoe, FairwayFatty voted this post useful.
  #3  
Old 11-28-22, 04:36 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,414
Received 163 Upvotes on 142 Posts
The 100 amp panel can be fed with up to a 100 amp feeder. It can be smaller. Aluminum cable will be much more economical to run than copper.

THHN is for use in conduit. It cannot be run in free air or through the studs.

Bathroom receptacles should be on 20 amp circuits.

With your list above you have maxxed out the number of spaces, 8.
 
CasualJoe, FairwayFatty voted this post useful.
  #4  
Old 11-28-22, 10:02 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 71,675
Received 3,332 Upvotes on 2,991 Posts
100A sub requires 4/0 copper or 2/0 aluminum.
Make that #4 copper and #2 aluminum.

4/0 is +200 amps.
 
FairwayFatty voted this post useful.
  #5  
Old 11-28-22, 10:22 AM
P
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 1,890
Received 229 Upvotes on 195 Posts
#2 Al for feeding subpanel is limited to 90A per the NEC.
#1 Al is needed for 100A.
 
FairwayFatty voted this post useful.
  #6  
Old 11-28-22, 11:50 AM
Z
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 6,406
Received 357 Upvotes on 319 Posts
I agree with Caddymac's statement. What are your anticipated loads in the loft? If it's just a bathroom plus some receptacles/lights, you can get by with a 30A feed. If you're running a water heater, heater/AC, then you're probably looking at a 60A feed.

100A is a lot of power and probably not required for your loft space. As mentioned, it's definitely worth getting a 100A panel for the breaker spaces, but then feeding it with 30/40/60A cable and breaker in your main panel as needed.
 
FairwayFatty voted this post useful.
  #7  
Old 11-28-22, 10:53 AM
F
Member
Thread Starter
Join Date: Dec 2005
Location: Virginia
Posts: 266
Received 1 Upvote on 1 Post
Could I use #2 Copper (By-the-Foot) 2 Black Stranded CU SIMpull THHN Wire
If so:
Would 2 black, 1 white and 1 green (what size green would be needed?

They dont have #2 green would #6 green be sufficient for the ground?
 
  #8  
Old 11-28-22, 11:57 AM
F
Member
Thread Starter
Join Date: Dec 2005
Location: Virginia
Posts: 266
Received 1 Upvote on 1 Post
Are you after 100A for the sub-panel due to the future expected loads? Or just trying to size a panel with enough spaces?
Well I'm not sure I'd actually need the full 100A. Here is the loft layout i was thinking
50A apartment size stove/oven
20A microwave
20A refrigerator
20A entertainment center
15A bath and outlets
15A general lighting
15A general outlets
Thanks for the response and any suggestions.
 
  #9  
Old 11-30-22, 09:18 PM
F
Member
Thread Starter
Join Date: Dec 2005
Location: Virginia
Posts: 266
Received 1 Upvote on 1 Post
Does the attached load calculation of 59A look reasonable (large loft room with small bath) and would I need to go with an 80A (59*1.25=73.75) breaker and ok to use 4-4-4-6 copper on 20ft run? Larger SER wire seems to be hard to get local.
(Pending mini split fed by 200A in garage level not loft panel)

 
  #10  
Old 12-01-22, 05:55 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,414
Received 163 Upvotes on 142 Posts
You typically will not find larger cables with copper conductors. Aluminum will be 1/3 of the cost of copper, be easier to work with and weigh less.
 
 

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