another sub-panel question

Reply

  #1  
Old 04-13-16, 08:04 AM
Member
Thread Starter
Join Date: Apr 2016
Location: USA
Posts: 6
another sub-panel question

Hi all. Long time observer, first time poster.

I have searched all over the interwebs and read the code and think I have this straight. Just really looking for confirmation that what I am doing is correct. Thanks in advance for any replies. I have a lot of respect for the people who post to this forum as I have learned an untold amount from perusing here.

I am running a subpanel for a detached garage quite a distance away from the main in my house.

The plan is about 150' run in the house to get from main panel to back of exterior. Then about a 250' outdoor run to the subpanel.

Here are the details:
60 amp gfci breaker in main
2-2-2-4 AL SER through the house in walls/attic/drop ceiling of basement (I know this is big wire, I sized it based on the votage drop)
Exit house under deck
Sleeved SER outside under deck to JB under deck
Terminal strip in JB to transition to 2-2-2-4 AL USE MHF
AL USE MHF sleeved underground to JB on outside of garage
terminal strip in JB to transition back to SER
SER inside garage to subpanel

150' total SER
250' total MHF

At subpanel ground will be bonded to box and local ground rod, neutral isolated

All conduit will be 1.5".

Anyone see any problems with this? Any suggestions?

I am a little concerned about pulling the USE MHF. Anyone have experience with this. The run is basically straight. How far should my pull boxes be from each other. Any advice in general would help....

This is another maybe stupid question. I know the USE MHF is OK for direct burial but I want the protection of the conduit as this run is through some wooded areas and I am concerned with roots etc. Instead of installing gluded conduit run and pulling could I just install a stick at a onto the cable and just friction fit the conduit (not glue it)? I figure since it is direct burial this would be OK and the conduit is just there for redundancy so it doesnt have to be glued. Any thoughts on this?

Thanks again for any help.
Jimmy
 
Sponsored Links
  #2  
Old 04-13-16, 08:42 AM
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 781
400 ft is too far for 60A using #2 Al. The best you can hope for is 30A max load keeping the VD within reasonable limits. You need to use #2/0 MHF & SER. And you don't need a GFCI breaker for the feeding breaker. As far as code goes the conduit needs to be installed as a complete unit, glued up, then wire pulled.
 
  #3  
Old 04-13-16, 09:01 AM
Member
Thread Starter
Join Date: Apr 2016
Location: USA
Posts: 6
Thanks pattenp.
Can you provide the basis for your reply. Using a readily available online voltage drop calculator I came up with the following using #2 aluminum, 240 volt single phase, 2 conductors per phase, 400' @ 60 amps and got a voltage drop of 2.46%.

Is your response based on something other than voltage drop?
 
  #4  
Old 04-13-16, 10:08 AM
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 4,059
Not sure of the prices for SER and USE cable, but as long as you have a desire to run condiut for the length anyway, I would just run conduit and-to-end and use THWN wire pulled through. Larger AL cables are a beast to work with, and I would NOT want to try to pull them through more than a few feet of conduit sleeving.

I'm personally not a fan of all those junctions, just more failure points and larger junction boxes required.
 
  #5  
Old 04-13-16, 10:18 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,359
Did you use the one way,or round trip distance in the VD calculation?
 
  #6  
Old 04-13-16, 10:19 AM
Member
Thread Starter
Join Date: Apr 2016
Location: USA
Posts: 6
Thanks for the reply Zorfdt.

I'm not sure I can get rid of the junctions as it would be very difficult/impossible to sleeve anything in the house. Best I can tell there is no wire product available that can be buried in conduit and also put in a home without conduit. If there is I would love to hear about it. If not I will definately consider using THWN for the outdoor/buried portion though.
 
  #7  
Old 04-13-16, 10:22 AM
Member
Thread Starter
Join Date: Apr 2016
Location: USA
Posts: 6
PCboss, the calculator I used specifically said to input the one way distance which is 400'. FYI, This is the calculator I used
Voltage Drop Calculator

If anyone can validate my numbers using hand calc or a more reputable/trusted sources calculator I would appreciate it.
 
  #8  
Old 04-13-16, 11:04 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,295
Name:  voltage.jpeg
Views: 149
Size:  47.2 KB

Seems like right around 5% drop. Code recommends limiting feeders to a 2% drop in an FPN statement, but it is not an enforceable article of the code. Ultimately it is your choice as to what level of drop is acceptable as long as you satisfy the minimum required wire ampacity for the circuit, which in this case would be #4 aluminum for 60A.

This is almost certainly acceptable for most uses, but if you're planning a big woodshop or something along those lines where you'll be running larger motors you may want to consider larger wire.
 
  #9  
Old 04-13-16, 11:25 AM
Member
Thread Starter
Join Date: Apr 2016
Location: USA
Posts: 6
Thanks ibpooks,
Why do you use the "single set of conductors" setting? Since it is 240 I have two #2 AWG wires. For the calculation I performed I selected "two conductors in parallel". Am I mis-applying the calculator? I am going to try doing this with a hand calc to confirm but I am certainly not an expert. I would like to get this right the first time and would rather not have that large of a VD.
 
  #10  
Old 04-13-16, 11:59 AM
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 781
This is one of the most accurate VD calculators I've found on the web. http://www.nooutage.com/vdrop.htm

You do use single set of conductors, not 2 conductors in parallel. 2 conductors in parallel is when you have 2 conductors supplying the same side of the phase if that makes sense.
 
  #11  
Old 04-13-16, 01:29 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,295
Single set of conductors is the correct setting (two hots, one neutral, one ground). Two conductors in parallel is not used in residential wiring -- it is when each wire is doubled up (four hots, two neutrals, one ground); or more likely in three phase (six hots, two neutrals, one ground). It is done to carry a larger amp load where a single set of wires would be too thick or heavy to be practical to work with or some other varied technical and financial reasons. An example would be something like a 600A service.
 

Last edited by ibpooks; 04-13-16 at 01:58 PM.
  #12  
Old 04-14-16, 05:22 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,213
All conduit will be 1.5".
Assuming you'll still be using the 2-2-2-4 MHF, there is no way you would be able to make a 250 foot pull in 1 1/2" conduit, it's just too small. You'll find that the way the MHF is triplexed that the triplexing adds quite a bit more resistance to the pull. I definitely wouldn't use PVC conduit any smaller than 2" and think 2 1/2" might be better yet.
 
  #13  
Old 04-18-16, 10:24 AM
Member
Thread Starter
Join Date: Apr 2016
Location: USA
Posts: 6
Ok. so after going thru the previous discussion I am now going to use 2/0. I have ordered the following:
300 ft of 2/0-2/0-2/0-1 URD (2/0,2/0,2/0 & #1 Syracuse Underground Secondary Distribution Cable)
150 ft of 2/0-2/0-2/0-1 SER (2/0-3 Aluminum SER Cable w/ 1AWG Ground | Wire & Cable To Go)

The SER will be run from the main panel 90 amp breaker (which can accept the 2/0). I will have to use lugs for the 2/0 neutral and #1 ground at the main panel. SER thru the house (unsleeved) to the exterior JB - (sleeved for a short run when it exits the house (2" pvc).

Best I can tell I need a 16" long JB (straight thru with 2" conduit) and I'm thinking like 6" wide will do it. I will make the splices using burndy mechanicals (Blackburn #6 Type ASR Dual-Rated Splicer Reducer with Solid Barrier Wire Stop-ASR2506-B1-10 - The Home Depot).

Heres what I'm thinking for the URD:
Glued 2" PVC from JB to 24" underground. I will sleeve it underground with 2" PVC but my plan is not to glue it, just to slide it over the wire and friction fit the bell. My logic is this is direct burial and its deep enough for direct burial. The conduit is just for "extra" protection from roots, rodents, etc. therefore not gluing is acceptable. The reasoning is I think it would be pretty tough to pull this stuff even thru a 2" conduit.

Appreciate the help so far. Any thoughts/input on my plan is appreciated.
 
  #14  
Old 04-18-16, 12:50 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,659
SER thru the house (unsleeved) to the exterior JB - (sleeved for a short run when it exits the house (2" pvc).
If your SER is not rated for wet locations check with your inspector. The NEC is somewhat vague on if conduit on an outside wall is a wet location. NEC says if it can be exposed to rain such as wind driven rain it is a wet location. Or did I misunderstand and you are not planning to run the SER for a short distance in conduit on an outside wall?
 
  #15  
Old 04-18-16, 06:37 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 11,982
Just because you have a 60 amp breaker for the feeder does not mean you use that number for your voltage drop calculation. You need to use the actual expected load which you would have to realistically figure out.

I would not use conduit for the outside run. I would use direct burial wire.
 
  #16  
Old 04-19-16, 08:12 AM
Member
Join Date: Feb 2016
Location: United States, Virginia
Posts: 781
SER is rated for above ground wet locations. It can be placed in conduit above ground for protection.

If you put conduit underground you need to install it correctly. If you ever need to replace the wire due to a defect or problem the unglued connections could present a problem removing and installing wire. Besides, NEC requires the conduit to be completely assembled prior to installing wire.
 
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
'