Detached Shed/Garage Subpanel

Reply

  #1  
Old 06-22-15, 10:55 AM
D
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 3
Received 0 Votes on 0 Posts
Question Detached Shed/Garage Subpanel

First post so bear with me here. First will be a description of what I have going on followed by a few questions.

Planning to wire a small 60a sub panel in my detached shed/garage. Panels will be located approx. 100 cable feet apart. In my shed I do not plan on running any large tools or equipment. Panel is for lights and receptacles. I currently have 2" pvc conduit run 18" underground with two 90 degree "stub ups" (one behind the shed and one outside the house opposite the main panel)
Stock photo of subpanel for reference:
[ATTACH=CONFIG]52307[/ATTACH]
Shop Siemens 16-Circuit 8-Space 125 Amp Main Lug Load Center at Lowes.com

Questions:
- 60a 2pole breaker at the main panel. The panel shown above has no "Main" breaker. Would backfeeding a main (60a 2pole) breaker per the manufacturers instructions or a separate 60a disconnect/enclosure feeding the buses be preferred? Since I do not need more than 6 circuits backfeeding would not be a spacial issue.

- Cabling: #6/3 romex would be allowed while inside either structure (home and garage) but would not be allowed in the buried conduit correct?
Southwire 125 ft. Black 6-3 Romex NM-B W/G Wire-63950002 - The Home Depot
I am under the impression from researching that NEC views the outdoor PVC as a wet condition and that I will need (4) #6 THWN cables instead or a #6/3 UF cable. Ideally running the #6/3 NM-B the entire length would be easiest though.

- Would a LB fitting be best to penetrate into the home? My plan for the garage end is to use an LB and penetrate under the panel near the floor level. If #6/3 romex is not allowed per NEC would I need to use the romex from:
[Main panel -> LB penetration] then splice to #6 THWN for the length to the next LB? The same would go for the other end as well. So it would look like this-
Main Panel---[#6/3]---LB*Splice*---[(4)#6 THWN]---LB*Slice*---[#6/3]---Subpanel

- I know I will need to drive a dedicated ground rod for the sub panel but will I need to install a floating neutral bus? The sub panel currently only has 1 neutral/ground bus.

- I noticed the other day my duct tape caps that I used are starting to deteriorate. What would be the easiest way to remove any water buildup in the conduit? I haven't checked how much is in there and I don't know how long the duct tape has had openings. My current plan is to break out the shopvac unless someone has a better idea. Then I'll reseal them a little better this time.

Sorry for the lack of knowledge and numerous questions. I have done plenty of electrical work around the house and on job sites (when I was younger) but I have never tackled this specific job before especially on my own home. I want to make sure that I get this right the first time without any complications. I can also provide pictures if needed.

Thank you in advance!
 
Attached Images  
Sponsored Links
  #2  
Old 06-22-15, 11:18 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
Would backfeeding a main (60a 2pole) breaker per the manufacturers instructions or a separate 60a disconnect/enclosure feeding the buses be preferred?
Yes. You will need a retention clip. Depending on the cost of the breaker a unfused 60a A/C pull out disconnect might be cheaper.
6/3 romex would be allowed while inside either structure (home and garage) but would not be allowed in the buried conduit correct?
That is correct.
NEC views the outdoor PVC as a wet condition and that I will need (4) #6 THWN cables instead or a #6/3 UF cable. Ideally running the #6/3 NM-B the entire length would be easiest though.
Easiest to pull in conduit is individual conductors. If you want to use the UF best to just bury at 24" and skip the conduit except for protection above ground. However since the conduit is there I'd suggest just use THWN.
- I know I will need to drive a dedicated ground rod for the sub panel but will I need to install a floating neutral bus? The sub panel currently only has 1 neutral/ground bus.
You need to buy and add a ground bar. The neutral must be isolated. Only neutral wires on the neutral bar.
What would be the easiest way to remove any water buildup in the conduit
Water is expected in conduit and is normal. You can vacuum it out but it will probably fill again.
Would a LB fitting be best to penetrate into the home? My plan for the garage end is to use an LB and penetrate under the panel near the floor level. If #6/3 romex is not allowed per NEC would I need to use the romex from:
The NM-b can enter a weather proof box mounted to the outside wall if it enters at the back. At that point you can make your splices to THWN in the box.
 
  #3  
Old 06-22-15, 11:45 AM
D
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 3
Received 0 Votes on 0 Posts
Yes. You will need a retention clip. Depending on the cost of the breaker a unfused 60a A/C pull out disconnect might be cheaper.
$11 for the breaker
Shop Siemens QP 60-Amp Double-Pole Circuit Breaker at Lowes.com
The retention clip can't cost too much so I think this option will be the cheapest.

Easiest to pull in conduit is individual conductors. If you want to use the UF best to just bury at 24" and skip the conduit except for protection above ground. However since the conduit is there I'd suggest just use THWN.
I'm searching for THWN conductors at the local big home improvement stores and can't seem to find any. I'll have to do more research to find an electrical supplier locally.

edit: found some at lowes! Title says THHN but in the description it says THWN. I will check the jacket in person.

You need to buy and add a ground bar. The neutral must be isolated. Only neutral wires on the neutral bar.
Will do!

Water is expected in conduit and is normal. You can vacuum it out but it will probably fill again.
The THWN is rated for wet conditions so I shouldn't need to worry about that?

The NM-b can enter a weather proof box mounted to the outside wall if it enters at the back. At that point you can make your splices to THWN in the box.
Perfect! That will certainly make it easy intead of ripping up a lot of the drywall under the main panel to run conduit I can just run the #6/3 down from the panel and splice in the LB.
 
  #4  
Old 06-22-15, 12:12 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 35 Votes on 27 Posts
For a 60 ampere circuit you only need a #10 copper equipment grounding conductor UNLESS the other conductors have been upsized to reduce voltage drop.

Do NOT attempt to splice in an LB fitting, it is generally too small.

Almost all THHN is dual rated as THHN/THWN. The W refers to weatherproof.
 
  #5  
Old 06-22-15, 12:13 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 43 Votes on 41 Posts
To avoid splices you can use a single piece of 6-3/g UF-B cable for the whole run. It can run through the building interior just like NM "Romex" and be pulled through the underground pipe. Normally UF is very difficult to pull through conduit, but since you have 2" pipe it will not be a problem.

I would do a backfed breaker at the shed panel -- keep it simple, no extra disconnects.

Virtually all THHN is dual rated THWN-2, double check the printing on the wire but I would be shocked if it was only THHN should you choose to go that route. Note that larger size LB fittings can be dual-purposed as splice boxes as long as the manufacturer has stamped a cubic inch rating on the fitting. I'm certain that 2" fittings should have that rating so that would make the transition of wire types easier.

To do the underground pull, use your shopvac to dewater the pipe and then suck a poly string through tied to a plastic shopping bag as a "sail". Then use your string to pull the wire while a helper pushes/feeds it from the other side to avoid skinning the wire or over tensioning the pull string. With 2" pipe you shouldn't really even need wire lube, but it couldn't hurt to grab some while you're in the electrical aisle.
 
  #6  
Old 06-23-15, 07:15 AM
D
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 3
Received 0 Votes on 0 Posts
Originally Posted by ibpooks
To avoid splices you can use a single piece of 6-3/g UF-B cable for the whole run. It can run through the building interior just like NM "Romex" and be pulled through the underground pipe. Normally UF is very difficult to pull through conduit, but since you have 2" pipe it will not be a problem.
125ft of UF-B cable at homedepot is $306.
Sourcing the other cable (NM + THHN) from homedepot as well comes to ~$395.

The lube is <$10 b/c I won't require a gallons worth.

Seems like the UF cable inside the PVC is the most cost effective route.
 
  #7  
Old 06-23-15, 04:56 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 10,640
Received 85 Votes on 75 Posts
I would do a backfed breaker at the shed panel -- keep it simple, no extra disconnects.
I agree, a backfed main breaker is usually my preference, but you'll need to purchase a Main Breaker Retaining Kit. The box stores probably won't have the one you need. The label inside the panel you purchase should list the appropriate catalog number for the one you need.
 
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
 
Ask a Question
Question Title:
Description:
Your question will be posted in: