A Little help please

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maintenanceman

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Hello all
This is my first post on this forum.

I was wondering if someone could help me with some calculations? Since I moved I cannot find a box of books that has all of my code and reference books.

here is my scenario.

My parents want a panel set in their barn and fed from the garage. the run is 230' and when the house was built the electrician ran a sch 40 1 1?/4" conduit.

The loads will be: lighting and convenience outlets with a table saw at the most. Also the possibility of a propane furnace at a later date.


My question is?

what size wire can I safely pull and still provide a usable sub panel at the barn, and what would the capacity of the sub panel be?

I hope I did not forget anything


Thanks
Steve
 
Re: A Little help please

The largest conductors I would try in this run would be three 2 AWGs and one 6 AWG EGC with THWN insulation.

If your situation allows the use of the grounded conductor as the grounding means you could go with just three 1 AWGs

Either way due to the distance and conduit size you are topping out at a 100 amp feeder more or less.
 
Re: A Little help please

why figure it as a 100amp ? it isnt a dwelling?

[ July 18, 2004, 06:45 PM: Message edited by: cs409 ]
 
Re: A Little help please

IMO it is not "the main power feeder to a dwelling" so Table 310.15(B)(6) can not be used and at 230' feet I would not plan on maxing out the conductors.

JMO, Bob :p

[ July 18, 2004, 07:13 PM: Message edited by: iwire ]
 
Re: A Little help please

Originally posted by iwire:

If your situation allows the use of the grounded conductor as the grounding means you could go with just three 1 AWGs

Click to expand...
So if I set a ground rod sized just right I can omit the #6 you mentioned? and if the Nuetral and ground terminals are connected I should separate them?
Also can I run the 2awg and just use a 75amp main at the sub panel and still be safe? since I just ordered it.

Thanks for all of your help

Steve
 
Re: A Little help please

Originally posted by iwire: If your situation allows the use of the grounded conductor as the grounding means you could go with just three 1 AWGs
Click to expand...
I don?t follow this statement. What situation would allow this?
Originally posted by maintenanceman: So if I set a ground rod sized just right I can omit the #6 you mentioned?
Click to expand...
As I mention above, I do not see how this would be allowable. The ground rod will not provide a low-resistance path back to the source to clear a possible fault. You still need a ground rod, since this is a separate building, but that does not eliminate the need for an Equipment Ground Conductor (EGC).
. . . and if the Neutral and ground terminals are connected I should separate them?
Click to expand...
Yes. I see this as a sub-panel. As such, it would require a separate neutral and ground bus, with separate conductors back to the panel in the garage. That means you would need a total of 4 wires: The two hots and the neutral can be #2, and the EGC can be a #8.
Also can I run the 2awg and just use a 75amp main at the sub panel and still be safe?
Click to expand...
Safe? Yes. Good design? No. Running 230 feet of #2 conductors and allowing the current to reach 75 amps, you can get a voltage drop as high as 6.71 volts, or just under 6%. For feeders, the NEC suggests limiting the voltage drop to 3%. So long as the actual current stays below 40 amps, the voltage drop should be acceptable.
 
Re: A Little help please

Charlie 250.32(B)(2) allows the use of the grounded conductor as the grounding means if you meet all the requirements of that section.

Steve, I would run the 2 AWGs, use a 100 amp breaker and feel confident that the load in this panel is not going to even approach 60 amps given your description of what you want to run.

If you think the load will exceed about 60 amps you will either have to live with voltage drop or install a larger raceway.


Bob
 
Re: A Little help please

By the way, no matter how this panel is installed, with a separate equipment grounding conductor or without one, you must connect to a grounding electrode. That will most likely mean installing a ground rod. :)

[ July 19, 2004, 04:40 PM: Message edited by: iwire ]
 
Re: A Little help please

Originally posted by iwire: Charlie 250.32(B)(2) allows the use of the grounded conductor as the grounding means if you meet all the requirements of that section.
Click to expand...
Thanks, Bob.
 
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