garage subpannel

Reply

  #1  
Old 01-04-07, 11:12 AM
Member
Thread Starter
Join Date: Jan 2007
Posts: 16
Question garage subpannel

I am putting a 60amp sub pannel in my new garage that is 100 feet away from the house and I ran 1 in. plastic electric conduit out to the garage. My question is the ground--- Im going to put an 8 ft ground rod at the garage and the ground wire should go where in the box? The house has the ground going to the neutral bar. should it be done like that or should i get the ground bar for the GE box? Also is 6 ga. for the lines and neutral and 8 ga. for the ground sufficient
 
Sponsored Links
  #2  
Old 01-04-07, 11:19 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Do you have any other metal paths between the detached garage and the house, such as a phone line, coax wires, water pipe, etc?

Did you run (or are you planning to run) three wires to the garage or four?

What size breaker are you putting in your main panel to power this circuit?
 
  #3  
Old 01-04-07, 01:09 PM
Member
Thread Starter
Join Date: Jan 2007
Posts: 16
no metal to the house. 60 amp from the house and i thought that i could save by running only three wires from the house pannel with the ground rod outside the garage pannel as previously posted
 
  #4  
Old 01-04-07, 01:34 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,332
Provided you have no other metal paths from the house to the garage, you can install (3) #6 copper THWN conductors to feed the 60A panel. The panel at the garage must have a main breaker if the panel is larger than 6 spaces. At the garage, you connect the grounds and neutrals from the branch circuits to the same bus bar, just like at a house main panel. Drive the 8' copper ground rod and connect it to the ground/neutral bar in the garage panel with a piece of #8 (or larger) copper wire.

If you end up deciding on a 4-wire feed to the garage, pull in a #10 bare or green insulated copper wire in addition to the #6s. The neutrals and grounds would be isolated on separate bars at the garage panel, but the ground rod and main breaker would still be required as above. In this case, the GEC (wire to the ground rod) would attach to the add-on ground bar in the panel.
 
  #5  
Old 01-04-07, 02:08 PM
Member
Thread Starter
Join Date: Jan 2007
Posts: 16
Completely understood! Thank you. On a side note when i pulled the main breaker cover off to install the 60 breaker I noticed that an electrician we had redo the basement after a remodel pulled stranded wire into the box on some new breakers which i thought was sub code but after rading a few posts , maybe not. Do they use this so its easier to pull thru existing conduits, and is it code?
 
  #6  
Old 01-04-07, 02:22 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,332
> stranded wire

It's easier to pull through conduit and is completely legal. Stranded wire can be more difficult to correctly splice and terminate for a novice, so it is not usually recommended for DIY work.
 
  #7  
Old 01-04-07, 03:47 PM
Member
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
Originally Posted by ibpooks View Post
> stranded wire

It's easier to pull through conduit and is completely legal. Stranded wire can be more difficult to correctly splice and terminate for a novice, so it is not usually recommended for DIY work.
not to hijack this thread, but you just cleared something up for me.

For some technical reasons about the way a wire carries current, stranded is actualy in many cases better than solid. I always wondered why some specs want solid.

Now I realize that it is because the stranded is often not spliced correctly.

Thanks man
 
  #8  
Old 01-23-07, 06:49 AM
Member
Thread Starter
Join Date: Jan 2007
Posts: 16
Ground wire

After looking and thinking at this I decided to pull a 4th wire for a ground just in case of future things that may give the garage a ground path to the house. Once pulled where is the proper spot to tag the ground wire from the sub pannel to the house?
 
  #9  
Old 01-23-07, 06:53 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
At the main panel the ground connects to the ground buss, which may also be the neutral buss.

At the sub panel you need separate ground and neutral buss bars. All ground wires, including the wire from the ground rod and the ground wire from the main panel, connect to the ground buss which is bonded to the panel. All neutral wires, including the neutral wire from the main panel, connect to the neutral buss whichn is NOT bonded to the panel.
 
  #10  
Old 01-23-07, 07:08 AM
Member
Thread Starter
Join Date: Jan 2007
Posts: 16
ground locatoin

The 8 ga. wire run from the sub pannel gets connected to the neut buss at the main pannell? Just rechecking. The ground and neut busses have been isolated in the sub.
 
  #11  
Old 01-23-07, 07:38 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Connect the ground wire to the ground buss in the main panel. Period. Done.

This may or may be the same buss as the neutral buss.
 
  #12  
Old 01-23-07, 07:41 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,332
If you mean the ground wire, yes. The subpanel ground wire get connected to the ground/neutral bus in the main panel. In a MAIN panel, the ground and neutral bus are the same; in subpanels they are isolated.

If you haven't bought the wire yet, the ground wire to the subpanel only needs to be #10, not #8.
 
  #13  
Old 01-24-07, 09:08 AM
Join Date: Jul 2006
Location: Southeast MI
Posts: 77
Harley,

If you're going with 60A service to the garage, then the minimum is #6AWG for distances of less than 30'. While #6 solid is rated for 55A, #6 stranded is OK, for less than 30'. For greater distances, de-rate it one size to #4 to accomodate voltage drops. Stranded is easier to work with, and better because of its greater surface area because AC currents are concentrated at the surface of the conductor, and not evenly spread throughout the conductor like DC.

You need to de-rate the current capacity of the wires if you exceed 30' (in your case 100'). Don't mean to rain on your parade, but if you want to draw 60A, #4 copper is the minimum required. If you've already laid the feedline and it's too much to dig it up, then just de-rate the tandem breaker feeding it to, say, 50A

Hope this helps,

Steve
 
  #14  
Old 01-24-07, 09:27 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,332
Steve (Circuit Breaker),

Could you cite some NEC article numbers and calculations to support your claims?

Table 310.16 lists the 75deg ampacity of #6 THWN at 65A and makes no distinction between solid and stranded. Additionally, minimizing voltage drop may be a reasonable design consideration, but it is not required. Still, at 100' and 60A voltage drop is only 2.4% which is well within acceptable tolerances. The OP is just fine with a 60A #6 THWN feeder as planned.
 
  #15  
Old 01-26-07, 10:45 AM
Join Date: Jul 2006
Location: Southeast MI
Posts: 77
Not sure of the chapter-and-verse of the NEC for wire sizes, but in just about every Homeless Depot & Lowe's, I see a well-done display of all the wire-by-the-foot they carry. I can't remember, but when I go out and run errands this afternoon, I'll check. I will have to make a note of the ampcity of both the Cu and Al of the various AWGs before I comment further.

Also, I got mixed up between solid-v-stranded as opposed to Copper-v-Aluminum. At 60Hz, there is little difference (if any) in the ampacity of solid-v-stranded.
 
  #16  
Old 01-26-07, 11:00 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,332
Consider this a public service announcement against the electrical advice given by the big box stores.

> display of all the wire-by-the-foot they carry.

I've seen that chart, and I will say that it is wrong for nearly every situation; it is never as simple as gauge X wire = Y ampacity. When calculating ampacity for a given installation, you must consider:

1) the AWG of the wire
2) the type of metal
3) the temperature rating of the insulation and terminations
4) if the conductor is part of a cable or installed in conduit
5) the properties of all other conductors which share the conduit
6) ambient temperature

Once the above criteria are satisfied, then you can consider upsizing the conductors to meet less than 3% voltage drop over the distance of the run.
 
  #17  
Old 01-29-07, 10:39 AM
Join Date: Jul 2006
Location: Southeast MI
Posts: 77
The table I see at: http://xtronics.com/reference/wire_gauge-ampacity.htm
shows #8 is rated at 46A (derated to 40A), & #6 is rated at 60A (derate to 55A). So, you can use #8-3Cu, and for your 5kW setup, this is fine. But, if you upgrade to a 10kW unit (41.6A @ 240V), you will need to go with #6-3Cu.
 
  #18  
Old 01-29-07, 11:39 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,332
> The table I see

Did you read the first line of that table? It's clearly a reference for engineering communications equipment, not premises wiring.

"The following information may have errors; It is not permissible to be read or used by anyone who has ever met a lawyer. Use is also confined to Engineers with more than 370 course hours of electronic engineering and should only be used for theoretical studies."

It doesn't really matter what any other table says anyway. The only table(s) that matter are those which are part of the National Electric Code, specifically 310.16 for ampacities.
 
  #19  
Old 01-29-07, 05:04 PM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,455
"Also, I got mixed up between solid-v-stranded as opposed to Copper-v-Aluminum. At 60Hz, there is little difference (if any) in the ampacity of solid-v-stranded."

There is NO difference in the eyes if the NEC.

All this is a moot point anyway. Where would you find solid #6THHN or NM cable anyway?
This is not even worth talking about IMO.
 
  #20  
Old 01-29-07, 05:07 PM
Member
Join Date: Jan 2007
Location: Piedmont
Posts: 92
Actually, the default column of table 310.16 to use is the 60 degree column, because the circuit is less than 100 amps (NEC 110.14(c) ). In this case, the number 6 wire is only rated for 55 amps. Number 4 is good to 70 amps in the 60 degree column, and in this scenario would only drop 3.696 volts @ 100 ft.; well within the 2% allowable maximum voltage drop for a feeder. Go with the number 4 if you want the job done within code.
 
  #21  
Old 01-29-07, 05:11 PM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,455
Voltage drop on feeders is 3%, not two.
Also, this 3% voltage drop limit is a suggestion. NOT a code requirement.
 
  #22  
Old 01-29-07, 05:22 PM
Member
Join Date: Jan 2007
Location: Piedmont
Posts: 92
When it's in the book, you use it. Read article 215.2 (d) FPN No.2 carefully and you'll see that the maximum allowable voltage drop for a feeder is 2%.
 
  #23  
Old 01-29-07, 05:28 PM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,455
I use "the book" every day, and night.
 
  #24  
Old 01-29-07, 05:30 PM
Member
Join Date: Jan 2007
Location: Piedmont
Posts: 92
That's great....so do I, when I need to. Don't want to be argumentative, so I'll agree to disagree.
 
  #25  
Old 01-29-07, 05:56 PM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,455
A good read on voltage drop:

http://www.mikeholt.com/technical.php?id=technicalvoltagedrop1
 
  #26  
Old 01-29-07, 06:15 PM
Member
Join Date: Jan 2007
Location: Piedmont
Posts: 92
I'll check it out.
 
  #27  
Old 02-17-07, 10:54 AM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
Originally Posted by joshmack View Post
When it's in the book, you use it. Read article 215.2 (d) FPN No.2 carefully and you'll see that the maximum allowable voltage drop for a feeder is 2%.

Sorry I'm late to the party but joshmack, if you are going to claim to be knowldgable, you had better understand what you think you knwo.

You need to read and understand what a FPN is and what weight it has regarding the code use of them.

BTW; if all will go to the back of the NEC and look into the specs for conductors, you will find there is a difference in resistance between solid and stranded conductors but the difference in negligable when determining the ampacity of the conductors and is not considered for the NEC's determination of the ampacity limitations.

and don't even get me started on the BB stores and their posted ampacities of conductors They are often wrong or are given for a condutor being used in a specific situation (such as resiential service entrance conductors)

They should not be used nor depended upon.
 
  #28  
Old 04-08-07, 04:31 PM
Member
Thread Starter
Join Date: Jan 2007
Posts: 16
gfci breaker

Finished project and all is well. Wanted to put in gfci breaker for outdoor water features. With seperate ground and neutral bars, does the tail of the breaker go to the neut. bar or the ground bar?
 
  #29  
Old 04-08-07, 04:45 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
neutral bar
 
  #30  
Old 04-08-07, 05:22 PM
Banned. Rule And/Or Policy Violation
Join Date: Feb 2006
Location: North of Boston, MA.
Posts: 2,113
Glad to hear it all went well. Now button it up,
Riding season is upon us.No time to finish winter projects.
 
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
'