Protecting UF-B above grade

Reply

  #1  
Old 08-13-08, 07:25 AM
B
Member
Thread Starter
Join Date: Jul 2006
Location: Maryland
Posts: 70
Received 0 Votes on 0 Posts
Protecting UF-B above grade

I will be burying UF-B between my house and shed to install a sub panel in the shed. It will come out of the ground at the foundation of the house and rise about a foot before it enters the crawl space. How do I protect the wire at this spot from damage?

Also, my power needs for the shed will be 2 florescent light fixtures, an outlet for power tools, a treadmill, and possibly a portable heater in the winter. It is very unlikely that I would ever use power tools and the treadmill at the same time, but more likely that I'd use a portable heater (or window a/c) and the treadmill or power tools at the same time.

I was guided to use 6/3 UF-B with a 60 amp double breaker at the house panel, separate grounding rod at the shed. Sound good?

Thanks,
Brian
 
  #2  
Old 08-13-08, 09:01 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,581
Received 13 Votes on 11 Posts
Sounds like you might not need a sub panel. For your needs a multi-wire circuit using 12-3 and a 20a 240v breaker might be all you need. (cheaper then #6 plus a sub-panel.)

The UF can be protected with a short length of PVC conduit where it leaves the ground. If you want to go with a multi-wire circuit and no sub you could run conduit all the way and use #12 THWN instead of UF. That way you could easily add a sub panel later if your needs change and you needed more power.
 
  #3  
Old 08-13-08, 09:22 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Originally Posted by brian6 View Post
How do I protect the wire at this spot from damage?
A sleeve of PVC conduit from the bottom of the trench up to an LB fitting which turns into the house.

I was guided to use 6/3 UF-B with a 60 amp double breaker at the house panel, separate grounding rod at the shed.
I think the 60A panel with #6/3 cable is a massive overkill for your listed needs. I would instead urge you to consider a 20A multiwire circuit using #12/3 or #10/3 cable depending on the distance between the house and shed. The multiwire circuit essentially provides you with two 20A circuits in one cable; it also eliminates the need for a subpanel and ground rod. A simple disconnect switch is all that's required at the shed. This option will be much cheaper and still meet your needs.
 
  #4  
Old 08-14-08, 10:04 AM
B
Member
Thread Starter
Join Date: Jul 2006
Location: Maryland
Posts: 70
Received 0 Votes on 0 Posts
Thanks for the replies. I wanted to read up on multi-wire circuits before I asked more questions.

In the panel: I understand it's important to have each leg be connected to opposing bus bars. Will installing a 20a 240v breaker automatically accomplish this? Then shared neutral and ground get hooked up to their respective panel bars.

In the shed:
I'm having a little bit more trouble understanding exactly what will happen in the shed. I will have one outlet at the workbench for tools, one outlet at the treadmill, one outlet on the other wall of the shed for portable heat/ac, overhead florescent lights controlled by a switch. I would also like to have an exterior flood light that would be switch-controlled. Can someone walk me through this? Which disconnect switch do I buy? My main panel is Square-D. A quick google search brought dozens of results back.

Also, distance from house to shed is about 130 feet, but total wire run between panel and shed will be closer to to 170 feet due to obstacles and best path. Should I use #10/3 (or #10 THWN, haven't decided conduit vs. direct burial yet)?

Thanks,
Brian
 
  #5  
Old 08-14-08, 10:56 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Originally Posted by brian6 View Post
Will installing a 20a 240v breaker automatically accomplish this? Then shared neutral and ground get hooked up to their respective panel bars.
Yes, it will. In fact areas that follow the 2008 NEC a 240V double-pole breaker is mandated for multiwire circuits.

Can someone walk me through this?
Sure, you terminate the 12/3 (black,red,white) MWC in a junction box with a DPST (double pole single throw) switch just inside the building. From that box, you extend two 12/2 (black,white) cables which from that point on can be treated as completely separate 20A circuits. In the "split box", you connect all the grounds together, all the whites together, and the black and red from the supply to separate poles of the switch. You then connect the remaining two black wires to the two remaining terminals on the switch. The switch is now a "building disconnect", and the 20A MWC is split into two 20A circuits for use within the building. It would be a good idea to put the treadmill and the A/C or heater on separate legs.

total wire run between panel and shed will be closer to to 170 feet due to obstacles and best path.
That distance would really be pushing the edge of #12 capability. I would urge you to consider #10 if your budget allows.

Should I use #10/3 (or #10 THWN, haven't decided conduit vs. direct burial yet)?
Conduit is a little more pricey, and of course more work. Since you describe this building as a "shed", I don't see that there's much value in planning for future expansion which conduit would allow. I think this is a good fit for UF-B cable.

You'll also need to provide GFCI protection. You can do this by either using a double-pole GFCI breaker in main panel or by installing GFCI receptacles as the first two devices after the split described above. The breaker is more expensive (usually about $100), but allows you a 12" burial depth for the cable. The receptacles are of course cheaper and you don't have to walk as far to reset a trip, but the required burial depth is 24".
 
  #6  
Old 08-14-08, 11:44 AM
S
Member
Join Date: Dec 2006
Location: orange county
Posts: 285
Received 0 Votes on 0 Posts
Question

ibpooks ? I know you are one "fine electrician" (one of the greats on this site) but did you not mean a DPDP switch instead of a DPST as the disconnect switch for the multi-wire circuit. Why can't I picture a DPST?
 
  #7  
Old 08-14-08, 12:00 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,581
Received 13 Votes on 11 Posts
Sidecutter, DPST switch is correct. It has four screws (two on each side). The lines connect to one set of screws and load to the other. Think of it as two single pole single throw switches with a common throw.
 
  #8  
Old 08-14-08, 12:21 PM
S
Member
Join Date: Dec 2006
Location: orange county
Posts: 285
Received 0 Votes on 0 Posts
Thank-you Ray, another cup of coffee is needed (lol). I had in my feeble head, a three way switch of sorts. Yawn
 
  #9  
Old 08-14-08, 12:21 PM
B
Member
Thread Starter
Join Date: Jul 2006
Location: Maryland
Posts: 70
Received 0 Votes on 0 Posts
I will use #10/3. Considering I was about to run #6 and a sub-panel, it actually made my day getting quoted the price on #10!

Do I still extend #12 from the junction box for the two circuits, even though I'm using #10 as the feed?
 
  #10  
Old 08-14-08, 01:21 PM
S
Member
Join Date: Dec 2006
Location: orange county
Posts: 285
Received 0 Votes on 0 Posts
Talking

I'm quite certain that you would "of course" use 12awg for your 2-20 amp split circuits, (the pros will verify). If you look in the archives #25819 you will see a nice homemade drawing of how to install your two GFI receptacles, if you plan to go the GFI receptacle route that is.
 
  #11  
Old 08-14-08, 01:34 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Yes, you can use #12 inside the building after the split.
 
  #12  
Old 08-14-08, 01:45 PM
B
Member
Thread Starter
Join Date: Jul 2006
Location: Maryland
Posts: 70
Received 0 Votes on 0 Posts
sidecutter, how do I access the archives?
 
  #13  
Old 08-14-08, 02:34 PM
S
Member
Join Date: Dec 2006
Location: orange county
Posts: 285
Received 0 Votes on 0 Posts
Smile

At the very bottom of your page you will see a narrow 1/4 inch strip (gray backing). Push archive, then scroll to Electrical A/C -DC and "walla", you have at your disposal about 30,000 or so of these posts. Put it in your favorites. There is also a search engine (you have to join the club) No Fee Whoopee "hey that rhymes"
 
  #14  
Old 08-15-08, 11:17 AM
B
Member
Thread Starter
Join Date: Jul 2006
Location: Maryland
Posts: 70
Received 0 Votes on 0 Posts
OK, as I plan this out on paper I have a few more questions as they relate to multi-wire circuits...

Circuit 1 will have 1 gfci outlet, 2 florescent fixtures switch-controlled, 1 exterior flood light switch-controlled.

1. Does the gfci outlet need to be the first thing on this circuit?
2. From what I understand, I am not to directly connect the neutral to the terminal screw on the gfci, but instead wire-nut the neutrals in the box and extend a pigtail from the box to connect the neutral to the outlet? (Is that what is meant by mechanically splicing the neutrals?) And is it good practice to do the same with the hot wire?
3. For the switches, can I still do single-pole configuration? I would like to isolate each light to it's own switch, so I would have three switches. OK to run the line into the switch box, triple pigtail to the terminal screws, then extend from there to each fixture, bonding all the neutrals together and all the grounds together?

Circuit 2 will have 1 gfci outlet (the first), and one regular 15a outlet. More simple, but related to above, if pigtail is required per NEC, how do I terminate the neutral at the second outlet?
 
  #15  
Old 08-15-08, 12:40 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Originally Posted by brian6 View Post
Does the gfci outlet need to be the first thing on this circuit?
Yes, and it needs to be wired with LINE and LOAD so as to provide downstream protection.

From what I understand, I am not to directly connect the neutral to the terminal screw on the gfci, but instead wire-nut the neutrals in the box and extend a pigtail from the box to connect the neutral to the outlet? (Is that what is meant by mechanically splicing the neutrals?)
The mechanical splice requirement on the neutral only applies to junctions that are "pre-split" in the MWC. Once you split the MWC into the separate circuit legs as described in my previous post, you may treat the legs as if they are separate circuits (splice neutrals through receptacle screws, GFCI receptacles, etc).

And is it good practice to do the same with the hot wire?
Not required, but allowed.

For the switches, can I still do single-pole configuration?...
Yes, it's okay as you described.
 
  #16  
Old 08-22-08, 02:25 PM
B
Member
Thread Starter
Join Date: Jul 2006
Location: Maryland
Posts: 70
Received 0 Votes on 0 Posts
Is this the right DPST switch?

http://i257.photobucket.com/albums/h...s/DSC00346.jpg

I got this from my local electrical supply...I explained my setup as above, this is what they gave me. Just want to make sure.

It is labeled 20A-120/277V. FED SPEC W-S-896E. You can't see from the photo but it has screws on either side.

My feed will be #10.
 
  #17  
Old 08-25-08, 12:28 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Brian, it looks like that switch will do just fine. I believe that all of the Cooper spec-grade devices are rated for use with #14-#10 wire.

When wiring the switch, the #10s should both either be on the two top screws or the two bottom screws, but not on the same side of the switch.
 
  #18  
Old 08-26-08, 11:07 AM
T
Member
Join Date: May 2001
Location: Dry Side of Washington State
Posts: 738
Received 0 Votes on 0 Posts
2008 NEC does not allow using romex inside the shed unless you sheetrock the walls. Check with your AHJ in your area to find out which specific year NEC is in force.
 
  #19  
Old 08-26-08, 01:25 PM
R
Member
Join Date: Sep 2001
Location: Yorktown, VA
Posts: 322
Received 0 Votes on 0 Posts
"2008 NEC does not allow using romex inside the shed unless you sheetrock the walls. Check with your AHJ in your area to find out which specific year NEC is in force."

I was bitten by that one. However, I only had wire exposed in two stud cavities and he allowed me to use peg board to cover them up. I don't know whether he was doing me a favor or not.

Also, once I powered my shed up, I was required to install a light on the outside by the door....don't know whether that's NEC or local.

One more thing. Ipbooks (or someone), please correct me if I'm wrong, but aren't you supposed to make sure that your conduit protecting the wire at each end has an "L" at the bottom of the trench so that the wire exits in the direction of the trench?
 
  #20  
Old 08-26-08, 02:32 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Originally Posted by Randy Mallory View Post
"2008 NEC does not allow using romex inside the shed unless you sheetrock the walls. Check with your AHJ in your area to find out which specific year NEC is in force."
This varies a lot based on the local inspector. Some don't care at all, some say that as long as the romex is inside the stud bays (not on the framing face) it's okay, and some want to see plywood/sheetrock/conduit protection.

Also, once I powered my shed up, I was required to install a light on the outside by the door....don't know whether that's NEC or local.
I just looked that one up in the NEC. It specifically says "detached garages" in the requirement for outdoor lighting, so I guess your inspector was a little loose in the interpretation of garage.

aren't you supposed to make sure that your conduit protecting the wire at each end has an "L" at the bottom of the trench so that the wire exits in the direction of the trench?
Yes, the conduit should have a 90 sweep (~5" radius) between the horizontal and vertical to provide a gentle bend for the wire coming out of the ground.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: