subpanel in detached shop 170' away


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Old 01-19-14, 02:19 PM
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subpanel in detached shop 170' away

I have built a barn/shop on my farm and would like to run a 100 amp subpanel to it with at least 1 220v circuit and couple 110v circuits. I've received multiple wire size recommendations and I am now thoroughly confused. There will not be an electrical inspection in my situation as it is not required.

I need to run 170', meter to meter, of direct burial cable. What size aluminum would be the most appropriate? I want to run the cable myself and will more than likely have a pro hook up the panels after I pull the cable and wires as I am not sure I want to tackle that.

I've been told everything from 1/0 to 2-2-2-4 to #4... my guess would be 2224 but I don't have the experience (obviously) to make that decision.
 
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Old 01-19-14, 03:17 PM
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The fact you have a 100 amp subpanel does not mean you need to run 100 amps to it. The main breaker in the panel is only used as a disconnect so its size doesn't matter as long as it is equal to or greater then the supplying breaker. Assuming total amps of actual loads does not exceed 50 amps. three #4s and one #8 copper on a 60 amp breaker should be good. What will your actual loads be? That you haven't written and a conclusive answer can't be given till we know that.

Aluminum: three #3 and one #6.
 
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Old 01-19-14, 07:40 PM
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Small home auto shop...220v compressor and car lift sometime in the future; as wellas, other "regular" garage tools. Not a commercial shop or anything of the like. Will also have a "man cave" in the top
 
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Old 01-19-14, 09:04 PM
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We need loads, not volts. Please list amps or watts. Voltage drop is effected by the load on the circuit. If there is no load, there is no drop.
 
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Old 01-20-14, 03:34 PM
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220V
Heater - 20 amps
Compressor - 20 amps
Hydraulic Lift - 20 amps

110V
Forced air heater - 10 amps
Fluorescent Lights 18 x~1 amp
Garage door openers - 4 amps
Grinder - 10 amps
Drill Press - 12 amps
Drill - 12 amps
Chargers - 3 amps
Vac -5 amps
Video games console - 3 amps
LCD TV - 6 amps


Not an exhaustive list but for the most part this will be it
 
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Old 01-20-14, 06:28 PM
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Based on the loads listed, and using the voltage drop calculator here: Voltage Drop Calculator I would recommend at least #3 aluminum. Your 2-2-2-4 might be more readily available so you would be fine with that.
 
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Old 01-20-14, 09:27 PM
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Can i run 2-2-2-4 urd from panel to panel as long as it is in conduit once it enters the barn and inside the garage to the main? (I would probably run the whole length in conduct anyway)
 
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Old 01-20-14, 10:31 PM
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Can i run 2-2-2-4 urd from panel to panel as long as it is in conduit once it enters the barn and inside the garage to the main?
Only if it is rated USE-2.
338.24 ARTICLE 340 (NEC 2008)

(B) Underground Service-Entrance Cable. Underground
service-entrance cable (USE) shall not be used under the
following conditions or in the following locations:
(1) For interior wiring
 
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Old 01-20-14, 10:49 PM
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For some reason I thought i read that as long as the panel was within 6' of the entrance that it could be ran inside in conduit...oh well...
 
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Old 01-21-14, 08:04 AM
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Come up on the outside of the building and come into the back of the panel with an LB. I believe that URD is OK (As the inspectors around us approved it) as long as it is run into the panel the shortest distance possible, and in conduit.
 
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Old 01-21-14, 05:00 PM
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what dies LB mean?

Aaaaa@aaaaaaaaaaaaa
 
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Old 01-21-14, 05:04 PM
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Name:  LB_1.jpg
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L-shaped bodies ("Ells") include the LB, LL, and LR, where the inlet is in line with the access cover and the outlet is on the back, left and right, respectively. In addition to providing access to wires for pulling, "L" fittings allow a 90 degree turn in conduit where there is insufficient space for a full-radius 90 degree sweep (curved conduit section).

Source: Electrical conduit - Wikipedia, the free encyclopedia

.
 
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Old 01-27-14, 07:51 AM
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So I called my local codes and they told me to run 2-2-2 cable box to box using conduit and I would be fine. After talking to them, I think I may be able to wire it all up...Everything I have read on here says I need to use a 4 wire feeder, but codes guy said 3 wire is sufficient and to ground the subpanel to 2 rods outside the barn with #6. Then run the neutral from bar to bar inside the panels. So is it better to use 4 wire or is 3 ok?
 
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Old 01-27-14, 07:58 AM
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So is it better to use 4 wire or is 3 ok?
Current code requires a 4 wire feeder.

codes guy said 3 wire is sufficient and to ground the subpanel to 2 rods outside the barn with #6.
What version of the NEC has been adopted in your jurisdiction, are there any amendments to the adopted code?
 
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Old 01-27-14, 08:06 AM
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Code requiring 4 wires was adopted in 2008 I believe. If your location is not enforcing that code then you are not required to do it. I personally like the idea of 4 wires and separating the ground and neutral.
 

Last edited by Tolyn Ironhand; 01-27-14 at 10:07 AM.
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Old 01-27-14, 03:01 PM
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He didn't say...It was actually a city inspector since we don't have electrical inspections in the unincorporated part of my county. He just told me the following:

Run 2 #2 hots from a 90A breaker in the main panel to the lugs in the subpanel.
Run 1 #2 neutral from main bar to bar in subpanel
Ground subpanel bar outside the barn using #6 wire to 2 ground rods driven 8' deep, 6, apart.
Run the 2-2-2 direct burial 2' deep with red tape 6" above or run it in Conduit panel to panel
 
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Old 01-27-14, 03:10 PM
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IMO if that is the way he told you to do it, and he is the AHJ, than that is the way you should do it. If you do it that way, be sure to bond the neutral bar to the panel steel case.
 
 

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