Garage wiring questions

Reply

  #1  
Old 06-02-06, 11:40 AM
gastrek's Avatar
Member
Thread Starter
Join Date: Mar 2003
Location: USA
Posts: 27
Garage wiring questions

Hi,

I'm planning to wire a detached garage. I have a few questions:

1) I expect low load in the garage and will run a single 20A cirtcuit from the panel underground to the garage. I'll put a GFCI breaker in the panel for this circuit. I believe this allows the UF to be run only 12" deep, correct?

2) The panel is pretty far from the garage, maybe 50 or 60ft. To avoid a big voltage drop, I would like to use 10G for the UF. Can I then switch to 12G to wire up the garage? Is this allowed?

Thanks,

S.
 
Sponsored Links
  #2  
Old 06-02-06, 11:46 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Do not run a single circuit to the garage. That would be foolish. At the very least run a multi wire circuit to the garage. Best of all would be to run conduit, so that you can replace and upsize the wires when you need to.

Using a larger wire will certainly help with voltage drop. Yes, you could switch to 12 gage wire in the garage.

What will the wires be run under? Bare ground? a Garden? A walkway of any sort? A driveway?
 
  #3  
Old 06-02-06, 02:20 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,337
Originally Posted by gastrek
I expect low load in the garage and will run a single 20A cirtcuit from the panel underground to the garage.
At least use 12/3 cable for a multiwire circuit. This gives you twice the available power at a small increase in cost and no increase in work. Moreover, a multi-wire circuit cuts voltage drop in half when the load is evenly distributed.

I'll put a GFCI breaker in the panel for this circuit. I believe this allows the UF to be run only 12" deep, correct?
As long as you aren't running the cable under a driveway. It is a good idea to bury UF deeper, but 12" is the minimum if GFCI protection is provided before the trench.

The panel is pretty far from the garage, maybe 50 or 60ft. To avoid a big voltage drop, I would like to use 10G for the UF. Can I then switch to 12G to wire up the garage? Is this allowed?
Yes, as long as you size the breaker for the smallest wire on the circuit (#12 - 20A). Leave a note in the panel that there is #12 wire down the line so a future owner doesn't see the #10 and assume that he can use a 30A breaker.

50-60 feet really isn't that far; I would spend the money on 12/3 UF cable instead of 10/2 for the reasons I explained above.

My recommendation is that you install a standard 20A double-pole breaker in the main box, run 12/3 UF-B cable buried 18" to the garage. At the garage, install two GFCI receptacles (one for each leg of the multi-wire circuit 12/3). You will then have (2) 20A circuits off the LOAD terminals of the GFCI receptacles.
 
  #4  
Old 06-02-06, 02:50 PM
raider1's Avatar
Member
Join Date: Apr 2006
Location: Logan, Utah
Posts: 31
but 12" is the minimum if GFCI protection is provided before the trench.
Where are you getting this information?

Do GFCI receptacles constitute a disconnecting means as referenced in 225.30?

Chris
 
  #5  
Old 06-02-06, 03:31 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
Originally Posted by raider1
Where are you getting this information?

Do GFCI receptacles constitute a disconnecting means as referenced in 225.30?

Chris
In the table of burial depth, there is a column for: residential not over 120 volts to ground and gfci protected and max 20 amp.

Minimum burial depth is 12 inches based on this.


Table 300.5
--------------------------------------
the part I have a question about is this:

Moreover, a multi-wire circuit cuts voltage drop in half when the load is evenly distributed.
Could you point me to a calculation for this?
How would this be applied to 3 phase?
 
  #6  
Old 06-02-06, 03:49 PM
gastrek's Avatar
Member
Thread Starter
Join Date: Mar 2003
Location: USA
Posts: 27
more garage questions

Thanks for the input. I was under the (mistaken?) notion that if I ran a multiwire circuit to the garage with 12-3 (or 10-3 for that matter), I would have to add a ground rod at the garage(plus the extra 6" depth for the trench) Is this not necessary? I thought the code allowed only a sing branch circuit, 20A, protected by GFCI, without an added ground rod?

If this multiwire circuit is allowed without additional ground rod, how can I put a GFCI in the panel? I assume one is still required or does the 18" depth remove that requirement? I've never seen a GFCI for multiwire circuit.

What would I use as a disconnect at the point of entry? I was thinking I'd use a 20A switch, but for multiwire circuit, not sure what's required

Finally, this branch will run under the back lawn. I'll avoid the garden area....
 
  #7  
Old 06-02-06, 03:49 PM
raider1's Avatar
Member
Join Date: Apr 2006
Location: Logan, Utah
Posts: 31
Thanks I didn't see that column.

Chris
 
  #8  
Old 06-02-06, 06:33 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
While 12 inches is okay for a 120 volt circuit GFCI protected to an outbuilding, it might not be okay if you go the multi wire circuit route, which is what we strongly recommend you do, especially if you don't plan on installing conduit.

A multi wire circuit is considered a single circuit. No panel or ground rod is needed.

GFCI breakers are available in 240 volts. They have to be, as hot tubs and pools need them.
 
  #9  
Old 06-05-06, 08:42 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,337
Originally Posted by gastrek
I would have to add a ground rod at the garage...Is this not necessary?
A multi-wire circuit counts as a single circuit. No ground rod required.

If this multiwire circuit is allowed without additional ground rod, how can I put a GFCI in the panel? I assume one is still required or does the 18" depth remove that requirement?
You can use a 2-pole 20A GFCI breaker. They probably will not carry this item at a big box store; you will have to get it at an electrical supply house. It could even be a special order. Double pole GFCI breakers can be expensive (~$100+), so you may want to balance that against the extra 6" of trench. With a standard breaker, you need 18" depth; with GFCI breaker, 12" depth. Two GFCI receptacles in the garage will cost about $25, so you have to decide if the $75 is worth the trench depth.

What would I use as a disconnect at the point of entry? I was thinking I'd use a 20A switch, but for multiwire circuit, not sure what's required
You can use a double pole 20A switch or two single pole 20A switches.
 
  #10  
Old 06-05-06, 11:15 AM
Member
Join Date: Jan 2003
Posts: 111
The minimum cover for direct buried cable 24, unless under a residential driveway or under 2 or more in of concrete.
 
  #11  
Old 09-19-06, 09:58 AM
BOA's Avatar
BOA
BOA is offline
Member
Join Date: Oct 2005
Posts: 29
Originally Posted by Juhl
The minimum cover for direct buried cable 24, unless under a residential driveway or under 2 or more in of concrete.

Nec says 18" unless in conduit.
 
  #12  
Old 09-19-06, 10:17 AM
Member
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
Originally Posted by BOA
Nec says 18" unless in conduit.
BOA, if you are going to chime in three months after the thread was dead, you could at least post acurate information.

Table 300.5 showes depth to be 24 inches regardless of wiring method.
 
  #13  
Old 09-19-06, 10:33 AM
BOA's Avatar
BOA
BOA is offline
Member
Join Date: Oct 2005
Posts: 29
Originally Posted by jwhite
BOA, if you are going to chime in three months after the thread was dead, you could at least post acurate information.

Table 300.5 showes depth to be 24 inches regardless of wiring method.
I do apologize. I re-read nec. Sorry for the confusion on my part. Carry on..........
 
  #14  
Old 09-20-06, 07:41 AM
Member
Join Date: Jun 2006
Location: usa
Posts: 274
Wink

Originally Posted by jwhite

Table 300.5 showes depth to be 24 inches regardless of wiring method.
What about 300.5 Note 4? (2005)
 
  #15  
Old 09-21-06, 06:51 AM
BOA's Avatar
BOA
BOA is offline
Member
Join Date: Oct 2005
Posts: 29
Originally Posted by hillbilly ace
What about 300.5 Note 4? (2005)
Interesting....Would that be a gfci breaker or a gfci receptacle? Which end of the branch circuit?
 
  #16  
Old 09-21-06, 07:02 AM
Member
Join Date: Jun 2006
Location: usa
Posts: 274
Originally Posted by BOA
Interesting....Would that be a gfci breaker or a gfci receptacle? Which end of the branch circuit?
GFI receptacle or breaker on the supply end.
steve
 
  #17  
Old 09-21-06, 08:40 AM
Member
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
"
Originally Posted by jwhite

Table 300.5 showes depth to be 24 inches regardless of wiring method.
What about 300.5 Note 4? (2005)"

Good catch Steve I stand corrrected. I missed the GFI clause.
 
  #18  
Old 09-21-06, 12:28 PM
BOA's Avatar
BOA
BOA is offline
Member
Join Date: Oct 2005
Posts: 29
Wink

Originally Posted by jwhite
BOA, if you are going to chime in three months after the thread was dead, you could at least post acurate information.

Table 300.5 showes depth to be 24 inches regardless of wiring method.

Chime, Chime.....looks like we were Both wrong.
 
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
'