wiring subpanel

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  #1  
Old 05-10-04, 08:50 PM
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wiring subpanel

My property has a separate building on it that has 3 rooms. There is a dedicated circuit that runs to this building. The wire is 10/2 UF and runs about 120 feet. It just entered the building and then was split in junction boxes. My wife had 2 rooms in this building finished and the third is a garage. I plan to make the garage into a work shop with power saws, etc. The other two rooms may have a refrigerator, small window AC unit, treadmill, lights and other things. The question is, can I use this wire?? All my use will be 120v, but I wasn't sure if I had to run 240v to a subpanel? When the room was finished, a subpanel was put in but right now it is not in use. How would I wire a standard subpanel since I only have 2 strand + ground and right now only running 120v to the building??

Bill
 
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  #2  
Old 05-11-04, 05:13 AM
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The wire in place (10/2) is not large enough to supply power for a sub panel, at least not with the number of circuits you would need for power tools and the other items you mention.

You need to run new wire and properly power the sub panel. The aize wire you run will depend on exactly what you want to run at one time on the curcuits in this building.
 
  #3  
Old 05-11-04, 06:34 AM
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You don't need to run 240 volts, and you don't have to run 240 volts, but you do indeed want to run 240 volts out there. It would be a very poor design not to. So abandon the 10/2 and put in a 6/3 UF-B line and a small subpanel.

One key detail that you didn't mention that figures heavily into the design is the distance from your main panel to this building. Another key detail that is important is the square footage of this building. Based on these pieces of information, I may modify my recommendation in the first paragraph.
 
  #4  
Old 05-17-04, 06:54 AM
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I stepped it out (not the best but a rough number) and it is about 200ft. The two rooms in the building are about 12x12 each and the garage is about the same. So the rooms are 288 sq ft and a garage about 144 sq ft.

In the garage, I will only be running one tool at a time, along with about 300 watts of flourescent lights and a shop vac. In the other rooms, maybe a few lights and a frig, treadmill at one time.

I took my digital volt meter and took readings in the building and the voltage was the same as in my home? I guess I was expecting it to be lower from what I have read in posts about voltage drop when making long runs. I assume this is due to the resistance of the wire? Does this only lower available current? (I=v/R)

Bill
 
  #5  
Old 05-17-04, 07:44 AM
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Okay, so three insulated #6 copper wires plus a ground in conduit (or 6/3 UF-B) sounds good. Burial depth requirements vary depending on various factors. This will give you up to 9000 watts of power with acceptable voltage drop over 200 feet.

V=I*R is ohms law. Since I=0 when you made your measurement, then V is also 0, regardless of R. In other words, there is no voltage drop without current. Voltage drop increases as current increases.

Neither distance nor resistance lowers current. Every single electron you put in one end of the wire comes out the other end. However, distance and resistance lower available voltage and available power.

There's a lot of very important details to wiring a subpanel. Be sure to study up before beginning. You might want to consider letting an electrian wire it up. You can save costs by doing the digging yourself. Talk to the electrician first to find out how deep to dig the trench.
 
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