Treatment of Direct Burial Cable

Reply

  #1  
Old 06-16-15, 11:44 AM
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 4
Treatment of Direct Burial Cable

I am going to install a sub-panel in a detached garage. I am going to make it 100 amp service and was looking at using 2-2-4 AL URD or 2-2-4 Triplex available from the local home stores. As best I can tell by the tags and signage both of these are approved for direct burial, but no one can tell me how the wire is treated once it is run inside of either the home or garage. My first thought was in a PVC conduit, but some have told me it can be stapled up like you would non-metalic shielded cable. How does one correctly handle this type of cable inside a structure?
 
Sponsored Links
  #2  
Old 06-16-15, 11:57 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,365
The feeder needs to be 4 wires. The option to install a 3 wire feeder was removed from the code.

Not all cables can be used inside as well as direct burial. Regardless, individual conductors need to be in conduit.
 
  #3  
Old 06-16-15, 12:00 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,296
Three-wire feeds to outbuildings are no longer legal -- a four wire feed is required. Neither URD nor Triplex are allowed inside a building due to fire/smoke ratings. They must be terminated in exterior panels or junction boxes and continued indoors with a cable like SER, NM or THHN in conduit. Number 2 aluminum has a max ampacity of 90A, which is probably enough. If you actually need 100A you'll need a bigger cable.

I would instead recommend that you look at a product called mobile home feeder (MHF) cable. It can be used indoors in conduit, outdoors in conduit, and direct burial at 24" depth. You can probably find 2-2-4-6 or 2-2-2-4 through a local supplier.
 
  #4  
Old 06-16-15, 06:47 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
some have told me it can be stapled up like you would non-metalic shielded cable.
Who told you that? These are the people to NEVER ask for advice in performing electrical work!
 
  #5  
Old 06-16-15, 08:21 PM
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 4
Exactly why I wanted to get more clarification. Based on the design of the cable itself, that idea did not seem correct to me.
 
  #6  
Old 06-16-15, 08:42 PM
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 4
I checked at the local home store and I can get 2-2-2-4 mobile home feeder. 90 amps will suit my needs. Now I will turn to the question of conduit. The product is rated for direct burial, but reading around the Google-verse there seems to be a split on if direct burial is the way to go. Is the wiser option to run this through 1.5" schedule 80 PVC instead of direct burial?
 
  #7  
Old 06-16-15, 10:40 PM
Member
Join Date: Nov 2012
Location: USA
Posts: 3,132
Run the PVC conduit and pull individual conductors like THHN ,MTW, you will run the conduit in a complete run ,that way you eliminate any splicing, these conductors are much easier to work with,I usually run a pipe size larger than required by the NEC. Schedule 40 should be fine,1 1/2" seems small don't have the NEC handy.

Geo
 
  #8  
Old 06-17-15, 06:45 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,296
Pipe is optional -- the cable would will be better protected for a fairly small upfront cost. Using pipe is a great idea if you have rocky soil, if you know you'll be digging in that area in the future (garden, landscape), or if there will be vehicle traffic over the area. On the other hand, power companies have thousands probably millions of miles of buried XLP aluminum wire and it rarely goes bad unless there is a excavator involved.
 
  #9  
Old 06-17-15, 09:30 PM
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 4
I will look into this option as well. I am concluding I would still use 2-2-2-4 set of wires to feed a 90 amp sub-panel. 2 gauge copper rated at 95 and the 4 gauge ground rated at 70.

Thank you to all for the information so far. This is a work in progress so I am sure I will need more guidance.
 
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
'