Wiring For New Detached Garage

Reply

  #1  
Old 01-12-08, 12:02 PM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
Thumbs up Wiring For New Detached Garage

I recently had built a 24 X 26 detached garage, and I want to add electricity to it. I do not plan to use it as a work shop or have any heavy electrical loads in it. My plan is to have two overhead incandesant light fixtures (single light each) and three GFI receptacles inside and may be one outside. Later I will add two coach lights w/motion sensors to the outside front. The house main panel is in my old attached garage and is about 130 ft from my new garage. It is full but there are several breakers (actually 8 of 40) which are apparently not being used (old house). There is also one circuit which has on it only an outside receptacle and a pole light out front 50 ft from the house. From the size of the circuit breaker, I assume that it is a 240 circuit. My specific questions are: (1) Can I get by with just one circuit in the new garage and if so do I need a breaker in the new garage? (2) Can I use the existing 240 circuit, mentioned above, if I do away with the existing outside receptacle (this is only 65ft from the new garage)? (3) Or, should I put the new garage on one of the circuits not being used? (4) What size wire to the new garage do I need for your recommendation? Larry Lillard
 
Sponsored Links
  #2  
Old 01-12-08, 01:33 PM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
Received 0 Votes on 0 Posts
First off, An "OUTBUILDING" is only allowed to have 1 feed to it, so make it count.

Sizing is up to you, but as I said, make it count.You have No idea what the future may bring, and as such we cant either. Carefull planning at this stage is critical.

What you stated , 30 amps should be sufficient, but only you can determine what will be used and when.

I would use 2 of the "UNUSED" Breaker slots in the main panel, but first insure that they are NOT BEING USED, (They were put there for a reason at some point).

A subpanel in the new garage to distribute everything where you need it and you'll be set...
I know its kind of vague, But you have decisions to make, and as soon as you do , any of us here will be glad to help out with the details.
 
  #3  
Old 01-12-08, 09:25 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
I would go with a sub panel in the garage. 30 amps at the minimum.

If you refuse to put in a sub panel, then at least put in a 20 amp multi-wire circuit. At those distances, you do not need to upsize the wiring.
 
  #4  
Old 01-14-08, 08:56 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
(1) Can I get by with just one circuit in the new garage and if so do I need a breaker in the new garage?
It depends on what you intend to use the receptacles for. An occasional hand tool or shop vac would be fine. A 120V welder or table saw, probably not fine. You do not need a breaker panel in the new building if you only run a single circuit (or a multi-wire circuit), but you do need a disconnect switch near the point where the circuit enters the building.

Can I use the existing 240 circuit, mentioned above, if I do away with the existing outside receptacle (this is only 65ft from the new garage)?
No.

(3) Or, should I put the new garage on one of the circuits not being used?
Yes. Determine which old circuits are abandoned and disconnect them to free up spaces in the panel. Or you could use tandem breakers if your panel is rated for them.

(4) What size wire to the new garage do I need for your recommendation?
I would strongly recommend that you install 1-1/4" PVC conduit, buried 18". This will allow you to install your 20A circuit now with the ability to increase up to 60A or 100A in the future if your needs change.

For the proposed 20A circuit, I would pull #10 stranded THWN (black, white & green) into the conduit. If you choose not to use the conduit, use a 10/2g UF-B cable.
 
  #5  
Old 01-14-08, 12:51 PM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
Wiring For New Detached Garage(update)

Diesel, Bob, and Ben, thanks for your help. I have decided to take your advise (the reason I asked for it) and today I bought my Square D Homeline 4-circuit panel and two 15 amp breakers for it. I will have 2 circuits in the garage, one for the (4) lights and one for the (6) receptacles. On the receptacle circuit the first in line will be a GFI receptacle
wired to protect the remaining 5. I will feed the garage panel with a 3-wire 120/240 30 amp circuit from the main panel. I will use the one that was for the hot tub that the people I bought the house from took with them. It currently has a 50 amp breaker in it which I will replace with the 30 amp. I haven't decided exactly how to get from the main panel to the garage. I can't go completely underground
because there is a driveway and side walk to cross. From the main panel to the garage is a minimum of 100 ft but may require 150 ft of wire one way. Questions: (1) What size wire do I need for the feed? (2) How do I wire the receptacles so that the GFI protects all. Any and all suggestions will be appreciated.
Larry Lillard, MSAE Astronautical Engineer
 
  #6  
Old 01-14-08, 12:58 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
Unless you are running conduit you will be running a four wire feed to the garage. Use at least 8 gage wire to handle the voltage drop.

Follow the directions that come with the GFCI receptacle. They will tell you to connect the incoming power to the LINE terminals and the outgoing wires ton LOAD terminals so that the outgoing side is GFCI protected.

I suggest that you make the receptacle circuit in the garage a 20 amp circuit. In the long run you'll be glad you did.


Yes you can route cable under the driveway and under the sidewalk. You can rent tools to do so
 
  #7  
Old 01-14-08, 03:34 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Unless the driveway is really wide, it's not too bad to get underneath. You can use a length of conduit and a garden hose to make an improvised hydraulic drill and bore a tunnel under the drive.

Given the distance, #10 copper wire is borderline for a 30A subpanel. It couldn't hurt to bump up to #8 copper if you are willing to spend the money on the wire.

You can use the three-wire feed if there aren't any other metal pathways between the buildings (water line, cable tv, phone, etc). If there are any other metal pathways (or you intend to install them) then a four wire feed including hot, hot, neutral, and ground is required.
 
  #8  
Old 01-14-08, 03:49 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
My argument for a four wire feed is based on the possibility of some other metal path now or in the future, and because if you buy UF cable you will buy 8-3 or 10-3. which will include a ground.
 
  #9  
Old 01-14-08, 04:45 PM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
I hate to add this item but i have to remind few readers to be aware with the code change going on allready.

if your state do adopted the 08 code cycle you will face few big change along the way

mantory 4 wire feeder to any subfeed box [ 3 wire are no longer allowed anymore ]

everything in resdential garage have to be fully GFCI'ed that including the garage door opener and ceiling lights

for the rest of the readers i am sure modaiators will agree with this one PLEASE state your location [ it dont have to be a city just state because the NEC codes really varies a bit right now so to advoid confuseing just state your location so we can guide ya with correct code info.

Merci, Marc
 
  #10  
Old 01-15-08, 11:05 AM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
Thanks again to all that have made suggestions. I will use them. I misspoke when I said I would run a 3-wire feed. I meant two hot wires and a neutral plus a ground. I didn't realize there was a difference between a 3-wire feed and what I have just described; please explain the difference. As you suggested, I will use a #8 wire as the feed an a #12 in the garage. My location is south central (Sebring) Florida. Larry Lillard, MS Astronautical Engineer (retired)
 
  #11  
Old 01-15-08, 11:28 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
A three wire feed to a sub panel is one that has two hots and a neutral. There is no ground wire.

Presently these are allowed in some situations to an outbuilding, such as a detached garage. They are not as safe as a four wire feed (2 hots, a neutral and a ground), but they are cheaper. The longer the run the more money saved by not having the extra wire.

They are allowed when there is no other metallic path between the building where the supply panel is located and the outbuilding (where the sub panel is located).

When a four wire feed is used the ground and neutral remain isolated in the sub panel. When a three wire feed is used the ground and neutral are bonded at the sub panel.

A four wire feed means that another metallic path (such as a metal water pipe, telephone wire, coax line,etc.) can be added at any time between the buildings.
 
  #12  
Old 01-15-08, 01:17 PM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
Ok that make the diffrence and by the way the State of Florida allready in 05 code and should be on 08 code by now the last time i heard one of my electrician frenid from that state he informed me that.

so 4 wire feeder is fine and make sure you have everything GFCI'ed that including the lights.

Merci, Marc
 
  #13  
Old 01-18-08, 08:42 AM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
A Few Additional Questions

My current plan is to run a 4-wire, 30 Amp feed from my main panelboard to the remote panelboard in my new detached garage. I will keep the neutral and ground busses separated in the remote panel. The two planned circuits in the garage will be GFI protected by placing a GFCI receptacle as the first outlet in each of the circuits. I have been reading my books and your previous post on this subject and have learned a lot. Thanks for all of your information. My original plan has changed because of your suggestions. I want to get this right before I do any work. The additional questions are these: (1) How many 20-Amp circuits will the code allow me to have in the remote panel from the 30 Amp feed? (2) If I use 20 Amp breakers and 15 Amp receptacles, will the inspector pass this? Or more correctly, is this allowed? (3) Is it required that I drive a metal grounding rod into the earth at the garage? My interpretation of the Black&Decker book is that it is not, but I am not sure.
 
  #14  
Old 01-18-08, 08:48 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
1) As many as you want.

2) Yes, it is allowed.

3) You need to provide a proper ground for the sub panel, and a ground rod is usually easiest.
 
  #15  
Old 01-18-08, 12:09 PM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
3) You need to provide a proper ground for the sub panel, and a ground rod is usually easiest.[/QUOTE]

Doesn't the ground wire from the main provide this?
 
  #16  
Old 01-18-08, 12:16 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
The ground to the main panel and the ground to a ground rod(or other grounding device) are extremely different and serve different purposes.
 
  #17  
Old 01-18-08, 09:33 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
Study up a bit. Learn the difference between an equipment grounding conductor (EGC) and a grounding electrode conductor (GEC). As Bob says, they serve different purposes and protect you from different kinds of faults.
 
  #18  
Old 01-19-08, 11:56 AM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
Study up a bit. Learn the difference between an equipment grounding conductor (EGC) and a grounding electrode conductor (GEC). As Bob says, they serve different purposes and protect you from different kinds of faults.

John, you are right. I don't know enough about grounding, but here is my source of confusion. If the ground wire in the main panelboard is attached to a grounding rod and that ground wire is brought into the sub panel and attached to the ground bus there, won't all circuit ground wires in the garage attached to the ground bus be also connected to the ground rod at the main? Is it just because we need a shorter run for safety? Thanks all for your help.
 
  #19  
Old 01-19-08, 12:00 PM
Member
Thread Starter
Join Date: Jan 2008
Location: South Central Florida
Posts: 8
Received 0 Votes on 0 Posts
Also John, What is a good source to read up on this topic - grounding?
 
  #20  
Old 01-19-08, 12:17 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
The ground rods at the panel provide a path for current that comes from an outside source, such as a nearby lightning strike or a power surge on the main lines.

The ground wires that eventually connect the neutral to the neutral are to provide a return path for excess current that originates in the house, such as a hot wire touching the metal frame of a washer or dryer.
 
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
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: