Detached Garage Sub Panel Questions - Electrical - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 10-09-2010, 06:33 PM   #1
Newbie
 
Join Date: Sep 2008
Posts: 21
Rewards Points: 10
Default

Detached Garage Sub Panel Questions


I am planning to run 240 out to my detached garage for a couple of power tools and I want to make sure it will be done properly. The run to the garage will be about 80' and after doing a lot of reading this is my plan:

1. Install a double pole 60 amp breaker in my main 100 amp panel for the run.
2. Use #6\3 UF Direct Burial wire in a 24" deep trench.
- Is this generally cheaper than running separate THWN wires in conduit?
- Do I need 6\3 wire with a ground even though I am running the ground from the sub panel to the grounding rod? Seems redundant.
3. Install a 60 amp sub panel without a main disconnect.
4. Install a #10 AWG copper ground wire to a separate 8' ground rod.
5. Make sure the ground and neutral bars are separated.

I will be running a 240v table saw quite a bit and a 240v welder on rare occasions. Other than that it will pretty much be 1 or 2 20amp plugs and the rest 15amp plugs and general lighting. Any advice or corrections would be much appreciated.

Thanks,

Scott...

Advertisement

smuth10 is offline   Reply With Quote
Old 10-09-2010, 06:58 PM   #2
Just call me Andrew
 
Join Date: Mar 2009
Location: Albany, NY
Posts: 2,258
Rewards Points: 1,012
Default

Detached Garage Sub Panel Questions


1. Install a double pole 60 amp breaker in my main 100 amp panel for the run. Yes

2. Use #6\3 UF Direct Burial wire in a 24" deep trench.
- Is this generally cheaper than running separate THWN wires in conduit? I would use THWN in conduit. I think most areas only require 18" of cover, but check your local code.

- Do I need 6\3 wire with a ground even though I am running the ground from the sub panel to the grounding rod? Seems redundant. The grounding rods do NOT provide means to trip a breaker if there is a short. They serve very different purposes, so it's not redundant. The ground rod(s) dissipate a lightning strike. The ground back to your panel trips the breaker if a hot wire touches something it shouldn't (like the frame of your saw).

3. Install a 60 amp sub panel without a main disconnect. I believe you need a local disconnect since it's a detached building. You can use any size breaker (60 or above) since the feed is already protected up to 60A.

4. Install a #10 AWG copper ground wire to a separate 8' ground rod. I think you need 2 grounding rods...I may be wrong though.

5. Make sure the ground and neutral bars are separated. Yes, test with a continuity tester if not sure.

Advertisement

__________________
Andrew

secutanudu is offline   Reply With Quote
Old 10-10-2010, 09:26 AM   #3
Newbie
 
Join Date: Sep 2008
Posts: 21
Rewards Points: 10
Default

Detached Garage Sub Panel Questions


Thanks for the quick reply secutanudu.

So you don't think 6\3 wire is too small for that long of a run?

As far as the sub panel is concerned, I am a little fuzzy. I will check my local code to find out if it needs a disconnect or not, but why would I be able to put in a 100 amp disconnect breaker in the sub panel when there is only a 60 run out there?

Also, why do the ground and common bars need to be separated in this situation? I read they need to be, but have no idea why. In my main panel this is a bar coming across attaching the two.

Thanks again, Scott...
smuth10 is offline   Reply With Quote
Old 10-10-2010, 10:01 AM   #4
Licensed electrician
 
Join Date: Sep 2007
Location: Maryland
Posts: 8,001
Rewards Points: 2,800
Default

Detached Garage Sub Panel Questions


You can reference these stickies for subpanel installation.

http://www.dropshots.com/stubbie4#al...0Installations

The 100 amp at the outbuilding would just act as a disconnect.
__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.

Last edited by Jim Port; 10-10-2010 at 10:45 AM.
Jim Port is online now   Reply With Quote
Old 10-10-2010, 10:11 AM   #5
I=E/R
 
a7ecorsair's Avatar
 
Join Date: May 2010
Location: Minnesota
Posts: 2,052
Rewards Points: 1,000
Default

Detached Garage Sub Panel Questions


Quote:
Originally Posted by smuth10 View Post
Thanks for the quick reply secutanudu.

So you don't think 6\3 wire is too small for that long of a run?

As far as the sub panel is concerned, I am a little fuzzy. I will check my local code to find out if it needs a disconnect or not, but why would I be able to put in a 100 amp disconnect breaker in the sub panel when there is only a 60 run out there?

Also, why do the ground and common bars need to be separated in this situation? I read they need to be, but have no idea why. In my main panel this is a bar coming across attaching the two.

Thanks again, Scott...
#6 UF in copper is listed as 55 amps
#6 THWN in copper is listed for 65 amps
Quote:
why would I be able to put in a 100 amp disconnect breaker in the sub panel when there is only a 60 run out there?
because the 60 amp breaker in the main panel will protect the wire to 60 amps.
a7ecorsair is offline   Reply With Quote
Old 10-10-2010, 10:44 AM   #6
Newbie
 
Join Date: Sep 2008
Posts: 21
Rewards Points: 10
Default

Detached Garage Sub Panel Questions


Thanks for those drawings. It clears things up for me and I can get started. One last question of course. Can I buy a small 100 amp panel for the garage and then use a 60 amp breaker for the main breaker? I guess I don't understand being able to run a 60 amp service out from the main and then use a higher rated breaker out at the garage.

Thanks, Scott...
smuth10 is offline   Reply With Quote
Old 10-10-2010, 11:17 AM   #7
I=E/R
 
a7ecorsair's Avatar
 
Join Date: May 2010
Location: Minnesota
Posts: 2,052
Rewards Points: 1,000
Default

Detached Garage Sub Panel Questions


Quote:
Originally Posted by smuth10 View Post
Thanks for those drawings. It clears things up for me and I can get started. One last question of course. Can I buy a small 100 amp panel for the garage and then use a 60 amp breaker for the main breaker? I guess I don't understand being able to run a 60 amp service out from the main and then use a higher rated breaker out at the garage.

Thanks, Scott...
Think of this way. A light switch in your house turns a light on and off but the breaker protecting the wires is in the panel. The 100 amp breaker that would be in your garage will turn the garage on and off but the breaker protecting the wires from the main to the garage is protected by the 60 amp breaker. The individual circuits in the garage are protected by those individual breakers.
a7ecorsair is offline   Reply With Quote
Old 10-11-2010, 12:27 AM   #8
Just call me Andrew
 
Join Date: Mar 2009
Location: Albany, NY
Posts: 2,258
Rewards Points: 1,012
Default

Detached Garage Sub Panel Questions


Quote:
Originally Posted by smuth10 View Post
Also, why do the ground and common bars need to be separated in this situation? I read they need to be, but have no idea why. In my main panel this is a bar coming across attaching the two.
I had the same question...

Why can't you connect Ground/Neutral bus bars on a sub
__________________
Andrew

secutanudu is offline   Reply With Quote
Old 10-11-2010, 12:24 PM   #9
Member
 
Join Date: Feb 2010
Posts: 41
Rewards Points: 25
Default

Detached Garage Sub Panel Questions


"4. Install a #10 AWG copper ground wire to a separate 8' ground rod. "



Your grounding electrode conductor (the conductor that attaches to your electrode, which is a ground rod in your case) needs to be #8 minimum. I know this may be confusing since you only needed a #10 for the equipment grounding conductor from your main panel, but #8 is the required size from Table 250.66 in the NEC. Good luck

Advertisement

DetroitEE is offline   Reply With Quote
Reply


Thread Tools
Display Modes

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
60 amp sub panel for a detached garage canyonbc Electrical 32 01-11-2010 12:53 PM
wiring 100A to detached garage snowman Electrical 4 11-28-2009 05:53 PM
100 -> 200 amp panel upgrade questions philipjcaputo Electrical 1 10-30-2009 04:35 AM
Enhancing existing wiring to detached garage justinperkins Electrical 46 07-07-2008 08:29 PM
Replacement Meter Panel leonard_voet Electrical 19 04-09-2008 11:27 AM




Top of Page | View New Posts