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What gauge wire to run 90 feet underground to detached building

What gauge wire to run 90 feet underground to detached building

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  #1  
Old 09-17-14, 11:29 PM
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What gauge wire to run 90 feet underground to detached building

Hello everyone and hope you are all doing well. I have built a detached building in my back yard for jamming music with my band. From my main breaker in my garage..attached to the house I will install a 100 amp breaker and then run my wire to the building for my 100 amp sub panel. Only I can't get a clear answer as to what gauge wire to use for the 90' run. One told me #6, another said #4, another said #3 and lastly #2. Which should I use and to allow for any possible voltage drop? It will be underground inside conduit. And help to understand as I see three types like this and wonder what gives. One is listed at #3, another 3.0, and another #3 AWG. What's the difference and which should be what I use. Hopefully not too expensive too.

Thank you for any information.

mrcarl
 
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  #2  
Old 09-17-14, 11:36 PM
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Use #2 Aluminum for the hots and neutral, and #4 Aluminum for the ground.

Use #6 copper to connect to your ground rods.
 
  #3  
Old 09-18-14, 12:35 AM
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Hi Justin. I'm not sure why but I have been told to try if possible to steer clear of aluminum and go for copper. Know anything about why?
 
  #4  
Old 09-18-14, 05:29 AM
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That is for smaller branch circuit wiring. Larger feeder wiring is different, it is common to use aluminum. Breakers and lugs in most panels are designed for either. Just use anti oxidizer and tighten to specified torque.
 
  #5  
Old 09-18-14, 12:28 PM
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Aluminum is safely used everyday for feeders. I would not hesitate to use it. It also costs less than copper.
 
  #6  
Old 09-19-14, 09:34 AM
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Hi and thanks for the advise as I could use a break on the costs. Now when you say #2, #4...are you saying 2AWG or are you saying 2-0 alum.? And is there a difference? And again thank you for your advice.
 
  #7  
Old 09-19-14, 12:06 PM
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Now when you say #2, #4...are you saying 2AWG or are you saying 2-0 alum.?
2/0, copper or aluminum, is larger than #2. From #1, increasing numbers such as #2, #3 and #4 are progressively smaller wire sizes. From 1/0, decreasing numbers such as 2/0 and 3/0 get progressively bigger, 4/0 is bigger yet.
 
  #8  
Old 09-19-14, 03:46 PM
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Wire sizes commonly used, smallest (top) to largest (bottom:

#14
#12
#10
#8
#6
#4
#3
#2
#1
1/0
2/0
3/0
4/0
250 kcmil or MCM
etc.
 
  #9  
Old 09-19-14, 04:17 PM
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You need minimum #3 copper but #2 is sometimes more readily available (or #1 aluminum). The ground (EGC) will be #8 (#6 aluminum).
 
  #10  
Old 09-22-14, 01:18 AM
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Ok, so I found this and wanted to see if it would be correct in my case:

Aluminum URD Dyke 2-2-2-4 Cable direct burial quadruplex secondary wire

Would this be correct? And does this mean all 4 cables are wrapped together as One cable? And if this is used, what size conduit would I need to use to bury it?
 
  #11  
Old 09-22-14, 05:51 AM
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Conduit is optional except for protection where it enters and leaves the ground. It would need a maximum breaker of 90 amps. Unless dual rated USE-2 and individual wires marked such as xxhw it can't enter the building. 2" conduit.
 

Last edited by ray2047; 09-22-14 at 11:20 AM.
  #12  
Old 09-22-14, 08:35 AM
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URD has no overall jacket. The conductors are just twisted in a spiral as a group.
 
  #13  
Old 09-22-14, 10:54 AM
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I will be putting a 100amp breaker in my main breaker in the house which it would be coming from. I don't understand this "Unless dual rated USE and individual wires marked such as xxhw it can't enter the building." What does this really mean for a layman? I have a 100 amp subpanel I am going to, and don't have the cable yet so not sure what it is marked as, but there are 4 wires wrapped together in the pic. I can check with the shipper and see if it is dual rated USE and how the wires are marked then get back to you.
 
  #14  
Old 09-22-14, 11:17 AM
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It means a lot of URD doesn't have the flame rating to be used inside. The solution is simple. Place a box on the outside of the house and transition to a cable approved for that purpose. At he garage come up the wall and into the back of the box. Here is a discusion at a pro forum you might want to read: Urd
 
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