Proper way to wire a new sub panel in my attached garage?


  #1  
Old 12-28-16, 01:33 PM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
Proper way to wire a new sub panel in my attached garage?

I am planning to install a new sub panel in my garage. My concern is following proper procedure/code. I contacted the local building code office and confirmed that they follow the 2014 NEC.

My main panel is located in an interior room approximately 40 feet from where I would like to install a 70 amp sub panel. For the 70 amp sub panel, I would run 3 4 gauge conductors (2 hot, 1 neutral) and 1 6 gauge ground (all wires THHN/THWN). Since they are individual wires, I would have to use conduit, so I was planning to use between 1" and 1.5" sch. 40 PVC conduit from the main panel all the way to the sub panel.

Since the main panel is in a finished area, my only thought is to cut the drywall beneath it and feed the wires from the panel through the floor and into the crawl space.

I am planning to use between 1" and 1.5" sch. 40 PVC for the 30 ft run in the crawl space where the crawl space ends at a wall which has a utility closet on the other side located in my garage.

Drilling through this wall would put me into the utility closet in my garage between my gas water heater and a utility sink. My thought was to continue with the conduit 7 ft vertically, then turn and run approximately 4 ft horizontally (and over the utility sink), turn a corner and proceed another 6 ft horizontally until I arrive where I would like the panel to be which would require 1 last turn down and into the panel.

Does my plan seem ok, or have I missed a part somewhere?
 
  #2  
Old 12-28-16, 01:48 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,575
Received 15 Votes on 13 Posts
It seems okay. While 1" conduit is adequate I'd suggest 1" to make pulling easier. #8 copper would be adequate for ground.
 
  #3  
Old 12-28-16, 02:13 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,389
Received 148 Votes on 131 Posts
You cannot have more than 360 degrees of bend between pull points.
 
  #4  
Old 12-28-16, 03:10 PM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
Thanks. I was thinking I could use some LB fittings in place of some of the 90s to add extra pull points. Would that resolve the issue?
 
  #5  
Old 12-28-16, 04:06 PM
P
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 1,850
Received 210 Votes on 178 Posts
If using copper THHN in conduit, #6 is all you need for 70A. If using NM then #4 is needed.
 
  #6  
Old 12-28-16, 04:34 PM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
I thought I had to use the 60*C position on amp tables since I was working on 100 amps or less. Is that not the case?
 
  #7  
Old 12-28-16, 04:59 PM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
The breaker in the main panel feeding the sub panel and the main breaker in the sub panel would also have to be rated at 90*, correct? Otherwise I have to use the lowest temperature rating based on 110.14-C-1? Sorry for all the questions, just trying to make sure I understand before I get started.
 
  #8  
Old 12-28-16, 05:59 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,389
Received 148 Votes on 131 Posts
The 90 degree column is used for ampacity adjustments, aka derating.
 
  #9  
Old 12-28-16, 06:13 PM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
@pcboss - in that case, I would need to stick to my original plan of using the 60 or 75 degree columns depending on the termination points, right? So 70 amp service with 60 degree listings (or no listing at all) would require 4 gauge conductors or 6 gauge conductors with 75 degree terminations (assuming I can round up from the 65 amp listing in the NEC table)
 
  #10  
Old 12-28-16, 06:35 PM
P
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 1,850
Received 210 Votes on 178 Posts
THHN is 75 deg so #6 is 65A but you can use the next size standard breaker which is 70A. NM wire has to be sized at 60 deg. Breakers/panels are rated at 60/75 deg unless they are old.
 
  #11  
Old 12-28-16, 06:55 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,964
Received 595 Votes on 511 Posts
IMO - 70 amps is kind of an odd size. Most people tend to stick with 60 or 100 amps for ease of getting a breaker. While 70 amp breakers can be found at supply houses most home stores will only carry 60 and 100 amp ones on the shelf. Of course you can special order one. !
 
  #12  
Old 12-28-16, 07:16 PM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
Price wise, there doesn't seem to be much difference between 6 gauge and 4 gauge wire (quick search of Lowe's and Home Depot stuff sold by the foot) is there an advantage of one over the other besides the obvious increase in ampacity of the 4?
 
  #13  
Old 12-28-16, 07:33 PM
P
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 1,850
Received 210 Votes on 178 Posts
How did you come up with needing 70A? 60A breakers are cheap.
 
  #14  
Old 12-29-16, 04:08 AM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
I came up with 70 based on the equipment I am wanting to run. There is a heater that needs a 40 amp breaker and an air compressor that needs a 30 amp breaker. I also wanted to add at least one 120v outlet since I only have 3 in my garage.
 
  #15  
Old 12-29-16, 06:38 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,575
Received 15 Votes on 13 Posts
I came up with 70 based on the equipment I am wanting to run. There is a heater that needs a 40 amp breaker and an air compressor that needs a 30 amp breaker.
You don't determine supply by adding up the breakers. You use actual load you are likely to have at any time. In the case neither piece of equipment uses as many amps as their breaker and it is unlikely they both will be on continuously at the same time.
 
  #16  
Old 12-29-16, 07:27 AM
R
Member
Thread Starter
Join Date: Dec 2016
Posts: 8
Received 0 Votes on 0 Posts
In that case, I know for sure that the heater is 7500w and 240v which would be a 31.3 amp draw while running. For the compressors I am considering, one has a 15.7 amp draw and the other has a 22 amp draw both at 240v. If the heater and compressor were running at the same time, I would be pulling 53.3 amps - worst case. I would still like to add at least 1 120v 15 amp socket. It sounds like I would be ok to go with a 60 amp breaker, 6 gauge THHN/THWN wire.
 
  #17  
Old 12-29-16, 08:15 AM
P
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 1,850
Received 210 Votes on 178 Posts
You can always push it up to 70A if needed. The 60A breaker is about $10 vs. about $30 for the 70A breaker. $20 more is not a killer if you feel better with 70A.
 

Last edited by ray2047; 12-29-16 at 08:26 AM. Reason: #10 > $10
  #18  
Old 12-30-16, 04:37 AM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,964
Received 595 Votes on 511 Posts
I like to have more power available then less for future expansion. If you went with #4 copper wire you could bump up the breaker to 90 amps. The will be more then enough power for now and the future. As you said, the additional cost of the larger wire is nominal.

You will need 3 #4 THHN copper wires and 1 - #8 THHN for the ground. You mentioned this in your first post so you were on the right track all along.
 
 

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