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ribertgropius 06-07-2010 10:18 PM

Running power to small barn in VA from home service 350'
 
I want to run power from my existing home to a 24 x 36 2-story barn about 350' away. The barn consists of 3 garage bays on the lower level and one open workroom on the upper level. Here are the parameters:
  • The existing house has two 150 amp panels located side-by-side fed separately from the same meter. One panel feeds most of the house, the second feeds a small apartment in the basement. The panels have 30 spaces each, and both have room for spares, with the apartment panel especially light. The house was built in 1981. Both the house and the apartment have electric heat pumps and ranges. The house panel has a now unused 30 amp breaker for a former Kiln.
  • I would like to run the service underground, and could do a straight run from the corner of the house where the panels are located to the corner of the barn. Both ends would end up outside the buildings, where I would bring them up, penetrate the exterior walls, and run the wire to the panels within the structures. This approach means I would only have two 90's.
  • What I envision is putting a 60 amp panel in the barn to provide for lights and a few service plugs. It would certainly be nice to be able to run a 110 v compressor on occasion as well. Does 60 amp make sense? My understanding from other posts is that the panel needs a separate ground rod. I anticipate that I would have six circuits: one lighting and two plug circuits for each level.
  • Can I run this power from a 60 amp breaker in the apartment panel, or should I consider having a separate disconnect wired at the service entry for feeding the panel? I suppose I could also run individual circuits but because of the distance the panel would seem to offer more flexibility.
  • I assume I would run pvc, and am wondering what size wire and conduit I should use. How deep should the PVC be in Northern VA? The conduit will be crossing open field and there will be no traffic other than my tractor crossing it.
Thanks!

Robert

secutanudu 06-11-2010 07:30 AM

60A sounds fine. You can feed it from one of your existing panels. I do not think code allows you to run more than one circuit (or 2 in a MWBC) from one building to another.

Code says to go 18" deep to the top of the conduit if the circuit is not GFCI protected, and 12" if it is protected.

For 60A, run three 6AWG THWN and one 10AWG for the ground. The ground also has to be THWN (not bare wire).

According to this conduit fill calculator , the minimum size conduit you can use is:

3/4" Sched 80
1" Sched 40

Oversizing the conduit to 1" (80) or 1.5" (40) is not a bad idea.

You also need ground rods.

Scuba_Dave 06-11-2010 08:49 AM

I would run from the Main panel
You don't want to have to access an Apt in an emergency to shut down power
...probably never happen...but

1" conduit of a straight run is better then 3/4"
2 ground rods required at the barn

350' is a good distance & you need to account for voltage drop
In order to have 60a @350' with less then 3% drop you need #2 wire
For ~50a (load) you need #3 wire
For ~40a load you need #4 wire
For 30a load with #6 wire the voltage drop would be ~4.2%


For 60a load using #6 wire the voltage drop would be 8.3% which is a 20v drop

secutanudu 06-11-2010 08:57 AM

I didn't notice the long distance. Good call Dave.

brric 06-11-2010 10:59 AM

Quote:

Originally Posted by secutanudu (Post 454443)
60A sounds fine. You can feed it from one of your existing panels. I do not think code allows you to run more than one circuit (or 2 in a MWBC) from one building to another.

Code says to go 18" deep to the top of the conduit if the circuit is not GFCI protected, and 12" if it is protected.

For 60A, run three 6AWG THWN and one 10AWG for the ground. The ground also has to be THWN (not bare wire).

According to this conduit fill calculator , the minimum size conduit you can use is:

3/4" Sched 80
1" Sched 40


Oversizing the conduit to 1" (80) or 1.5" (40) is not a bad idea.

You also need ground rods.

Can you cite where in the NEC it says the grounding conductor must be insulated?

secutanudu 06-11-2010 12:44 PM

Quote:

Originally Posted by brric (Post 454539)
Can you cite where in the NEC it says the grounding conductor must be insulated?

Nope, guess I am wrong about that. Is that just for pools? I thought it was for wet-location.

ribertgropius 06-11-2010 08:24 PM

I took a measuring wheel to double check my distance today; am only 250'. Still need to bump to a heavier wire than #6?

And perhaps I misunderstood: I thought all I needed to run was three wires from the main panel, and then a separate ground at the new panel. I know I am missing something here...

Am I correct in thinking the two grounding rods are for the new panel in the barn: one for the ground and one for the common?

Thanks!

Robert

Scuba_Dave 06-11-2010 09:09 PM

Grounding rods are just for grounding, not for neutral/common

For 250':

In order to have 60a with less then 3% drop you need #3 wire
For ~50a (load) you need #4 wire

For ~40a load #6 wire woudl be a 4% drop = 9.5v

For 30a load with #6 wire the voltage drop would be 3% = 7.1v

secutanudu 06-11-2010 10:16 PM

I think maybe an explanation of the difference between the purpose of a grounding rod and a ground back to the panel is in order...I think I understand it.

I think that would explain to Robert (and me) exactly why he needs to run a 4th wire (the ground) from the main panel.

My thought is this....am I right....?

The ground rods are to dissipate a lightning strike to the building. Since this building is not connected to his main house, it needs its own rods.

The purpose of the grounding conductor in his conduit, which bonds the metal in his system to his main panel's neutral/ground buss bar, is to dump electricity from a ground fault back to the PoCo and trip the breaker to prevent a shock.

frenchelectrican 06-12-2010 02:18 AM

Quote:

Originally Posted by ribertgropius (Post 454855)
I took a measuring wheel to double check my distance today; am only 250'. Still need to bump to a heavier wire than #6?

And perhaps I misunderstood: I thought all I needed to run was three wires from the main panel, and then a separate ground at the new panel. I know I am missing something here...

Am I correct in thinking the two grounding rods are for the new panel in the barn: one for the ground and one for the common?

Thanks!

Robert

You may get away with 3 conductor set up only if you are on 2005 or 2002{one of the two } and earlier codes but if your are do required 2008 code then no you must use 4 wire feeder

But seriously I will still recomoned you run in 4 conductor set up so you don't have to worry about the code related issue come back and haunt ya.

but you will still have to use 35mm˛ { 2 AWG } conductor size and I mention copper here but if you want to use alum conductor you will have to bump up one size larger like 50mm˛ { 1 AWG }

For long run do not try to excessed 360° total bends but I rather keep at 270° or less it easier to pull.

with 35 or 50mm˛ conductors you will need 1.5 inch conduit size eaiser to pull with this distance and make sure you use plenty wire lube to make it slide easier.

Merci,Marc


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