Help on choosing UF, amp questions etc.

Reply

  #1  
Old 11-14-14, 07:36 PM
Member
Thread Starter
Join Date: Nov 2014
Posts: 29
Help on choosing UF, amp questions etc.

I've been building my own 300sqft shop and have gotten to the dreaded part where I need to wire. I have a 100A subpanel that'll connect, underground, to my 200A panel in the house, about 75ft away.

I've assessed my power needs to be around 50A, so I'm allowing for 60A. I plan on doing this myself with the help of a family member who has done a lot of wiring before, and I'll be getting permits/inspections as I need them. The question comes down to copper vs aluminum, though. I'll need a couple of 220V circuits so if I go copper I need 6/3UF, or if I go aluminum I go for #4Al, or 2-2-2-4 MHF I've seen it called.

Both can be direct buried but the copper costs 2.5 as much, and I really need to save money where possible. However, down where I am (Tennessee, though I'm from England (long story)) it seems the local tradesmen won't touch aluminum with a barge pole. Bad memories from poor aluminum wiring in the '60s and '70s apparently. However, if I can, I REALLY want to use this stuff due to the savings.

Leading on from that though, how am I going to connect these beastly cables to my main breaker? It's not going to be easy getting to the box, and am I going to need to run conduits? If I go with aluminum then I'm on my own and need to learn how to do it all by myself, because like I said before, the people down here are adamant that it'll burn the house down.

As I understand, for aluminum wire it's all about tight connections, no-ox and specific breakers rated for aluminum. Once inside the house though do I need to pigtail to anything to get it to the breaker?

Thanks.
 
Sponsored Links
  #2  
Old 11-14-14, 07:45 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,590
Sounds like some really have no idea about aluminum used for feeder vs the branch circuit wiring from the 70s. Two totally different animals. Aluminum conductors are safely used and installed every day.

The breakers will be rated for both copper and aluminum. No-alox is not needed but is a good practice.

Whether conduit is needed depends on your wiring method although a conduit sleeve may be needed coming out of the ground.
 
  #3  
Old 11-15-14, 12:07 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
Agreed with pcboss, there is nothing to fear with using aluminum cable for your panel feeder. Not only is today's aluminum cable a different alloy than in the 1970s, but the receptacle splicing problems that burned down houses simply aren't a problem with panel and breaker lugs which have been designed for use with aluminum.

It takes a little more technique to install it well, but it is something I'm confident you can do. Basically the only difference from copper is that you want to make sure the strands are clean after you strip off the insulation. Use a small wire brush to remove the oxidation from the surface of the aluminum strands, then apply a good amount of the no-ox compound with an acid brush. With copper or aluminum you need to torque the lug to manufacturer spec to make a good connection (too tight is as bad as too loose).
 
  #4  
Old 11-15-14, 09:36 AM
Member
Thread Starter
Join Date: Nov 2014
Posts: 29
Right. And so lastly, could you please help me out with the nomenclature on this #2Al?

I've seen it written as simply as 2 gauge aluminum, 2-2-2-4 mobile home feeder, triplex, quadplex, dyke wire, USE, URD and the list goes on.

Example: Search results for: '2-2-2-4'

Which would I want to get? Both the quad dyke wire and the SER are rated for wet use. Both are #2, both carry ~100A, but the quad dyke wire has 4 conductors and is stranded, whereas the SER has 3 conductors and is solid.

I don't want to have to junction it to get it inside the house and to the panel.
 
  #5  
Old 11-15-14, 10:06 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,590
SER is not for use underground. SER typically has 3 insulated and one bare conductor.

Any conductor #8 and larger will be stranded.

Triplex is 3 conductor, quadplex is 4.
USE underground service entrance. USE cannot be used inside unless it also has another rating for smoke spread.
 
  #6  
Old 11-15-14, 10:19 AM
Member
Thread Starter
Join Date: Nov 2014
Posts: 29
So can I use this and direct bury it, then run it in conduit from where it exits the ground to the panel?
 
  #7  
Old 11-15-14, 10:46 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,590
URD is underground residential distribution cable. I do not believe it can be used inside or in conduit.
 
  #8  
Old 11-15-14, 10:49 AM
Member
Thread Starter
Join Date: Nov 2014
Posts: 29
What about this?

Southwire specs state "Southwire mobile home feeder consists of four quadruplexed type RHH or RHW-2 or USE-2 AlumaFlex AA-8000 series aluminum alloy compacted conductors."

So all of Southwire's MHF products are suitable from panel to panel without conduit and direct bury, correct?
 
  #9  
Old 11-15-14, 05:11 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,391
So all of Southwire's MHF products are suitable from panel to panel without conduit and direct bury, correct?
Suitable for direct bury, yes. You still must use conduit where the MHF exits the ground up to a J-Box, disconnect or panel.
 
  #10  
Old 11-15-14, 07:26 PM
Member
Thread Starter
Join Date: Nov 2014
Posts: 29
Thank you so much for your help. I've now got to check local code to see if I need 4 wire to run the ground back to the box, or 3 wire and ground at the subpanel. Really appreciate your time on helping me out.
 
  #11  
Old 11-15-14, 08:15 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,053
I've now got to check local code to see if I need 4 wire to run the ground back to the box, or 3 wire and ground at the subpanel.
You need both if the subpanel is in a detached structure. You need an EGC (Equipment Ground) from the supplying panel and a GEC (Grounding Electrode Conductor) from a ground rod. Note some AHJs may require two ground rods.
 
  #12  
Old 11-15-14, 09:23 PM
Member
Thread Starter
Join Date: Nov 2014
Posts: 29
Oh, well my main panel will be grounded so I just need to ground at the subpanel, or add that to the list of things I'll leave to the electrician.
 
  #13  
Old 11-16-14, 06:58 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,590
The option of a 3 wire feeder was removed from the code.

Your service panel should already be grounded. Your new panel also requires a grounding electrode system.
 
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