SEP Ground Wire Choice - Electrical - DIY Chatroom Home Improvement Forum
Advertisement


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

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

Like Tree1Likes
  • 1 Post By Fishbulb28
Reply
 
Thread Tools
Display Modes
Old 12-11-2019, 03:23 PM   #1
Newbie
 
Join Date: Dec 2019
Posts: 3
Rewards Points: 6
Default

SEP Ground Wire Choice


I have a 400Amp Meter set/panel with (2) 200amp breakers in it.



One breaker feeds my house with 4/0 4/0 4/0 aluminum & #4 AWG USE-2 RHW aluminum green jacketed ground. This has been in service for several years.


The other breaker will feed my new garage 20 feet away from the meter set. My inspector told me I have to use 3/0 Copper (THHN) if I don't want to use aluminum. I am using copper. I have some #6 AWG (THHN) green jacketed Copper laying around. Can I use it for the garage ground?
All wire is/will be buried in PVC conduit. The 2.5 inch PVC burial for the garage has already passed inspection and is back filled.
Mattydale is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 12-11-2019, 04:26 PM   #2
Commercial. Const. ret.
 
surferdude2's Avatar
 
Join Date: Nov 2019
Location: Mousetown, southern Illinois, USA
Posts: 1,127
Rewards Points: 2,256
Default

Re: SEP Ground Wire Choice


Nope, #4 is required for 200 amps. Breaker size determines ground wire size.
surferdude2 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 12-11-2019, 05:16 PM   #3
Newbie
 
Join Date: Dec 2019
Location: Florida
Posts: 28
Default

Re: SEP Ground Wire Choice


What SD2 said.
ServiceCall is online now   Reply With Quote
Sponsored Links
Advertisement
 
Old 12-12-2019, 09:09 AM   #4
Newbie
 
Join Date: Dec 2019
Posts: 3
Rewards Points: 6
Default

Re: SEP Ground Wire Choice


Thanks for the responses.
The weirdest thing just happened- I was looking at my invoices and one of them was for #4 jacketed ground wire. So I went back out to the garage and looked at the spool of wire they shipped. It has 2 stickers on it over plastic wrap- one says #6 and one says #4. I had read "#6". So then I looked close at the wire instead of the sticker(s) and it is indeed #4 so I am good to go.
I was about to re-order the wire. Duh.
Thanks again for making me recheck.
Mattydale is offline   Reply With Quote
Old 12-12-2019, 02:47 PM   #5
Disrespectful to dirt
 
Fishbulb28's Avatar
 
Join Date: Jul 2016
Posts: 1,024
Rewards Points: 2,050
Default

Re: SEP Ground Wire Choice


Quote:
Originally Posted by Mattydale View Post
I have some #6 AWG (THHN) green jacketed Copper laying around. Can I use it for the garage ground?
#6 copper is absolutely fine for an equipment grounding conductor for a 200A feeder. #4 is not required so you are still okay if your conductor actually is #6.



The insulation type may or may not be a problem. THHN itself isn't allowed in a buried conduit or other wet location. Most name-brand wire produced recently will actually be THHN/THWN or THHN/THWN-2. Either of those are acceptable. You will need to look for this on the insulation itself, not the sticker on the spool.

Ironically, in this situation you can simply strip off the insulation if you have only THHN insulation.
Fishbulb28 is offline   Reply With Quote
Old 12-12-2019, 03:41 PM   #6
Commercial. Const. ret.
 
surferdude2's Avatar
 
Join Date: Nov 2019
Location: Mousetown, southern Illinois, USA
Posts: 1,127
Rewards Points: 2,256
Default

Re: SEP Ground Wire Choice


I think it takes #4 copper for the application that he's considering. You arrive at that rather circuitously (pun there) since a 200 amp breaker requires 3/0 copper and 3/0 copper run as a feeder to a building requires the ground conductor to be 60% of the ampacity of the feeders. I hope I remember that right.

Please bring me up to date if you know better. I don't want to mislead anyone, even if it's on the side of a bigger ground conductor than needed.
surferdude2 is offline   Reply With Quote
Old 12-15-2019, 12:47 AM   #7
Disrespectful to dirt
 
Fishbulb28's Avatar
 
Join Date: Jul 2016
Posts: 1,024
Rewards Points: 2,050
Default

Re: SEP Ground Wire Choice


Quote:
Originally Posted by surferdude2 View Post
You arrive at that rather circuitously
Circuitously? I don't how I could have been any more direct than going straight to the table. But if you want to take the long way around...

215.6 directs us to 250.32 as the feeder in question supplies a separate building.

Quote:
215.6 Feeder Equipment Grounding Conductor. Where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder shall include or provide an equipment grounding conductor in accordance with the provisions of 250.134, to which the equipment grounding conductors of the branch circuits shall be connected. Where the feeder supplies a separate building or structure, the requirements of 250.32(B) shall apply.
250.32(B)(1) states that 250.122 shall be used to size the EGC.

Quote:
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).

(B) Grounded Systems.

(1) Supplied by a Feeder or Branch Circuit.
An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
Surprisingly, 250.122 points us to Table 250.122 since the EGC is of a wire type.

Quote:
250.122 Size of Equipment Grounding Conductors.

(A) General.
Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as
provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

Equipment grounding conductors shall be permitted to be sectioned within a multiconductor cable, provided the combined circular mil area complies with Table 250.122.
And there we are back at Table 250.122 which shows a #6 copper EGC to be the minimum size for a feeder protected at 200A.

Quote:
Originally Posted by surferdude2 View Post
a 200 amp breaker requires 3/0 copper and 3/0 copper run as a feeder to a building requires the ground conductor to be 60% of the ampacity of the feeders.
There is no requirement, nor has there ever been, to size the EGC based on a percentage of the other circuit conductors' ampacity. Even so, 60% ampacity would require #1 copper, not #4.
jhil likes this.
Fishbulb28 is offline   Reply With Quote
Old 12-15-2019, 01:43 AM   #8
Commercial. Const. ret.
 
surferdude2's Avatar
 
Join Date: Nov 2019
Location: Mousetown, southern Illinois, USA
Posts: 1,127
Rewards Points: 2,256
Default

Re: SEP Ground Wire Choice


When I used the term "you" I didn't mean anyone specific, just any person in general. That's why I didn't use the past tense of "arrive" so it wouldn't refer to anyone in particular.

Perhaps I should have said "One can arrive" at that...

Anyhoo... As I said in the disclaimer, "I hope I remembered that right." It happened several years ago and the AHJ was the City of L.A., Dept. of Water & Power. I wasn't sure of the x% he told me but the u/g run was service panel feeder into a separate building from the main one. He insisted that the ground conductor had to be based on the feeder size rather than the breaker, although the breaker sets the feeder requirement. I felt that was a catch 22 but I got no mercy. I do remember he said it applied to feed conductors to a separate building. I just hooked the #4 on to the #six and slathered it well with yellow 77 and moved on. I didn't figure to ever need that information again since we rarely did runs to annexes, mostly single feeds to single buildings.

As a side note: Downtown L.A. still has a lot of lead sheathed cable for service conductors that have to be tapped when new businesses need upsized conductors. In my days there, the L.A.dept.W&P only had one elderly man who was allowed to remove that sheath and connect new taps. It had to be done live to keep all the other business going. I watched him start to do the deed... he used a very old and obviously well used pocket knife and wasn't the least bit nervous, although I was. I left the area as soon as I saw what he was about to do. I have no idea what size feed that cable was connected to but it had to be larger than 600 amps, since that was our requirement. Scary operation.
surferdude2 is offline   Reply With Quote
Old 12-15-2019, 05:58 PM   #9
Newbie
 
Join Date: Dec 2019
Posts: 3
Rewards Points: 6
Default

Re: SEP Ground Wire Choice


The inspector told me THHN was okay since it will be in conduit. I asked her specifically since I had not reordered the wire yet. Anyhow, I just checked the 3/0 and the #4 and they're both marked THHN/THWN so that base is covered... just in case. However- I have two 45's to go past the foundation and keep the LB flush on the wall and two buried 90's for the risers (only a 20 ft run)- and I don't think that should have passed (but it did)? Is two 90's the limit?
Mattydale is offline   Reply With Quote
Old 12-15-2019, 06:16 PM   #10
Commercial. Const. ret.
 
surferdude2's Avatar
 
Join Date: Nov 2019
Location: Mousetown, southern Illinois, USA
Posts: 1,127
Rewards Points: 2,256
Default

Re: SEP Ground Wire Choice


The NEC says no more than 360 of total bends, so four 90 or equal will be the max. You have two 90 degree bends and two 45 bends for a total of 270 of total bends. You're fine. In reality, it gets extremely hard to get a fish tale through and pull wire on even two 90 bends on very long runs.

SD2
surferdude2 is offline   Reply With Quote
Sponsored Links
Advertisement
 
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





Top of Page | View New Posts