Want to wire my garage for 220V using existing circuit.

Reply

  #1  
Old 07-09-08, 01:13 PM
Member
Thread Starter
Join Date: Jun 2008
Location: Co
Posts: 80
Received 0 Votes on 0 Posts
Want to wire my garage for 220V using existing circuit.

A previous owner of my house installed a subpanel right next to the main breaker with a sing double pole GFCI 50amp breaker. They an 8awg 4-wire romex cable about 30ft under my crawlspace to my deck (presumably for a hot tub). The breaker is currently thrown and the wire has just been sitting idle. I would like to add 220V service to my garage to support an old air compressor (no motor nameplate, so unknown current requirements) and potentially a table saw down the road. I am trying to determine the best approach for this project and have come up with a number of alternatives. My garage is connected to my house and is accessible from my crawlspace.

1. Replace the GFCI 50amp breaker with a 30amp breaker and reroute the 8awg cable to my garage and install a single 30amp wall receptacle.
2. Reroute the 8awg cable to a new subpanel to my garage with 1 30amp and 1 20amp breaker.
3. Same as #2, but replace the 8awg with 6awg cable. I would like to avoid this option since 6awg would require different conduit and more $.

I could list several other alternatives using different combinations of breaker size, wire gauge, or even removing the existing subpanel, but you get the gist of it. Right now, I am leaning towards option #1 since it will be the easiest to accomplish and I think I could get by only having 1 220V device running in my garage at any given time.
 
Sponsored Links
  #2  
Old 07-09-08, 01:31 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
First, you have to replace the 50A breaker with a 40A or less. #8 romex has a maximum rating of 40A.

I would recommend a 40A breaker on the feeder to a small subpanel in the garage, perhaps a 6 slot. This would allow you to install proper breaker sizes for the compressor and table saw in the garage. A small panel plus a couple breakers should only be about $30-40, so it won't add much to the cost of your project and leaves you with a much more flexible install.

Just running it to a 30A receptacle is probably too large for the table saw.
 
  #3  
Old 07-09-08, 02:45 PM
Member
Thread Starter
Join Date: Jun 2008
Location: Co
Posts: 80
Received 0 Votes on 0 Posts
Originally Posted by ibpooks View Post
First, you have to replace the 50A breaker with a 40A or less. #8 romex has a maximum rating of 40A.

I would recommend a 40A breaker on the feeder to a small subpanel in the garage, perhaps a 6 slot. This would allow you to install proper breaker sizes for the compressor and table saw in the garage. A small panel plus a couple breakers should only be about $30-40, so it won't add much to the cost of your project and leaves you with a much more flexible install.

Just running it to a 30A receptacle is probably too large for the table saw.
If I add a subpanel in the garage, is it OK if it is connected to the aforementioned subpanel and not directly connected to the main panel? In other words, is it OK to daisy chain subpanels?

After doing a Google for 40A GFI Cutler-Hammer breakers and seeing prices, is there any reason why the breaker would need GFCI? The panel is sealed.

Lastly, I've heard conflicting information about whether 8awg can be protected by a 50A breaker depending on the length of the run. At the very least, it seems to be fairly common non-compliance.
 
  #4  
Old 07-09-08, 04:00 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
You can use a standard breaker and GFCI receptacles. One GFCI receptacle can protect all receptacles on a 120v circuit. Lights and 240v supplies such as to a saw usually don't require GFCI protection.

There are special exceptions to the rules in certain cases for specific equipment such as welders or air compressors but here the general rule of 40a for #8 applies. You will need a ground rod at the garage.
 
  #5  
Old 07-09-08, 04:01 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by mears View Post
In other words, is it OK to daisy chain subpanels?
Yes that is okay as long as you maintain isolated grounds and neutrals.

After doing a Google for 40A GFI Cutler-Hammer breakers and seeing prices, is there any reason why the breaker would need GFCI? The panel is sealed.
No, you would want to use a standard breaker.

Lastly, I've heard conflicting information about whether 8awg can be protected by a 50A breaker depending on the length of the run. At the very least, it seems to be fairly common non-compliance.
The type of insulation on the #8 copper is what makes the difference.

#8 copper THHN conductors in conduit are limited to a 50A breaker.

#8 copper "romex" NM-B or UF-B cables are limited to a 40A breaker.
 
  #6  
Old 07-09-08, 04:02 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by ray2047 View Post
You will need a ground rod at the garage.
This is an attached garage, so no ground rod is required.
 
  #7  
Old 07-09-08, 05:18 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
Originally Posted by ibpooks View Post
This is an attached garage, so no ground rod is required.
My bad, missed that it was attached. Thanks for the correction.
 
  #8  
Old 07-09-08, 08:28 PM
Member
Join Date: Jul 2008
Posts: 23
Received 0 Votes on 0 Posts
Originally Posted by ibpooks View Post
#8 copper "romex" NM-B or UF-B cables are limited to a 40A breaker.
I have a very similar situation, where there is an existing NM-B cable with copper #8 3C with a #10 ground. The cable is currently wired to the main panel to a double-breaker for 220V (this circuit previously ran swimming pool pumps, which have been removed). Can this NM-B cable be used to serve a 110/220 subpanel, with a 40A breaker in the main panel for the feed? Or is that #10 ground restricting the feed to a lower rating? If it is, can I run an additional ground conductor parallel to the NM-B and tied to the ground bus bars at either end (main and sub)?

FYI, the subpanel will be in the same structure, a single-family house, with both the main and the sub in an unfinished basement. The main service, meter base/main breaker, and main panel were completely rebuilt to code in 1999, so the main already has an isolated ground from the meter base/main breaker.

Many thanks, RJ
 
  #9  
Old 07-09-08, 09:56 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
Can this NM-B cable be used to serve a 110/220 subpanel, with a 40A breaker in the main panel for the feed?
Yes.

Or is that #10 ground restricting the feed to a lower rating?
No.

....................
 
  #10  
Old 07-10-08, 05:10 AM
Member
Join Date: Jul 2008
Posts: 23
Received 0 Votes on 0 Posts
Thanks for the answers! RJ
 
  #11  
Old 07-10-08, 10:30 AM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
However let me step in here real quick.,,

If your area do use the 2008 code it will change a bit in the garage all the lighting circuit are required to be GFCI'ed that do including the GDO [ Garage Door Opener ] etc the only circuit it still not need the GFCI is the 240 volts equiment like 240 volt table saw or welder or compressor on that voltage don't need GFCI at all

Merci,Marc
 
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: