280 feet from pole

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  #1  
Old 09-15-10, 10:51 AM
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280 feet from pole

First post on the forum!

I'm building a cabin on my farm property and have a question for the forum on what might be the best way to power it up. I have a regular service pole that is roughly 280' from where I would bring service in to the cabin. Not sure of amperage at the pole (it feeds my house with a 200 Amp breaker on both sides) and looking to put 100 amp service at the cabin. Had planned to trench/conduit but wondering what might be best. Online calculators recommend 4/0 copper wire size for the distance and amps (200 at the pole and 100 at the cabin pannel) and seeing that has me a bit concerned over cost. Any ideas or suggestions as to how to do this as inexpensively would be very much appreciated!
 
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Old 09-15-10, 11:00 AM
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Is the meter located at the pole? Are there open breakers there to power the cabin?

Are there any connections between the cabin and house (water, phone, etc?)

Are you sure you need 100A there, have you done a load calc? If so I think you're looking at #2/0 aluminum USE (direct burial appx $4.50/ft). If a 60A service would do then #2 aluminum USE would be adequate (appx $2.50/ft). If this is a permitted job and the inspector believes the cabin is a "dwelling unit" you will have to do 100A; however most "cabins" would do just fine with 60A (maybe even less).

The USE-2 can be direct buried in a trench 24" or deeper. You could also install PVC conduit 1-1/2" or larger and pull in THWN or XHHW conductors. Overall conduit is a little more expensive and a fair amount more labor but the conductors are better protected.
 
  #3  
Old 09-15-10, 12:04 PM
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Thanks for the reply. The meter is at the pole with room for one more breaker. We could go 60 if we can make it work. Out where I live there is no building inspection / permits required. This is all new construction, so there is nothing there yet. I have not asked about a load assessment: the biggest users would be HVAC heat pump (hotel room style) rated at 6.7/7.3 ampers, F.I and 38.0 ampers, L.R. according to the literature if that helps. Next is a standard 60 gal electric hot water heater - no idea what that draws at the moment.
 
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Old 09-15-10, 01:15 PM
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With the two items you mentioned it would probably be best to go with 100 amps. In very cold weather the heat would be drawing over half your available current. The water heater and a stove could put you over 60a. Now if you went with straight AC no heat and propane for heat, water heater, and stove you could get away with 60a.

Explanation: Your heat pump will only be effective down to about 45 then the electric heat cuts in drawing high amps.
 
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Old 09-15-10, 02:45 PM
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Thought it might be tight as planned for 60 A. Do not have plans to have a cook stove however, so just the resistance heater and the HW heat and wont be taking many showers out there in the winter - this is going to be an office and occassional spring/summer/fall guest cabin for friends. Could add a propane tank out there for heat & HW, but really dont want to mess with it due to access to the truck needed to fill it.
 
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Old 09-15-10, 02:52 PM
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With that electric heater I agree that 100A is the way to go. It's about $500-600 difference, so not a huge bump but probably a good idea since you're close to the limit. If you had a wood stove or propane heat like some cabins do the smaller service would be okay so I thought I would mention it before we got too far into this.

About how big is the cabin? Does it have other electric loads like a stove, oven, laundry facilities?

Assuming you're going to go with 100A at this point here's what I recommend:

If you have a supply house nearby that sells Southwire brand they have a Mobile Home Feeder cable that would be perfect for you -- direct burial aluminum #2/0-2/0-1-4. Other manufacturers probably have something similar so ask about that at your dealer.

Otherwise you're going to buy individual conductor USE-2 in the correct sizes and tape the white and green yourself. If you go this way, be sure to price out a 1000' spool of #2/0 for the hots and neutral instead of per foot cuts; a full spool is often cheaper to cut your own then resell the leftover for scrap. The #4 ground will be best price by the foot.

You only need conduit on the vertical risers to a 90 sweep at the bottom of the trench. You'll want to trench at least 26-27" inches but I like to run a service deeper if you have a capable digging machine. Make sure there aren't any rocks in the backfill and the alum cables will last.
 
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Old 09-15-10, 03:03 PM
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Also, I suggest you look at this thread for many of the details about a panel install like ground rods and bonds. The third diagram down the list is for outbuildings.

http://forum.doityourself.com/electr...-drawings.html
 
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Old 09-15-10, 03:55 PM
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Originally Posted by ray2047 View Post
With the two items you mentioned it would probably be best to go with 100 amps. In very cold weather the heat would be drawing over half your available current.s.

Ray respectfully, 7.3 amps wouldn't be even close to half the 60 amp service..the 38amps is Locked rotor amps... the resistance heater if the unit had one might be a issue but would be fine if the draw was under 25 amps.

Ben
Certified HVAC-R and Electrical Maintenance Mechanic
 
  #9  
Old 09-15-10, 05:02 PM
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Braether3 I was seeing the 38a as the draw when the aux heating coils were engaged. I totally missed the "LR" designation. Thank you for the correction. True it may not have a resistance heater but I also doubt it would be that useful as a heater in severe conditions if it didn't and you would need a secondary heater.
O/T
Your the pro and I respect that so I'm happy to be corrected. Keep it up and maybe I'll learn something even at my age.
 
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Old 09-15-10, 05:17 PM
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Out where I live there is no building inspection / permits required.
Just curious, what towns are you near? How many square feet are in the planned cabin? I am also curious about how many KW electric heat will be necessary in cold weather after the heat pump loses it's efficiency.
 
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Old 09-15-10, 07:49 PM
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A quick rough thumb of rules for staight electrique heat system it will use about 10 watts per sq foot.

That with standard insluated building.

Super insluated building will use less but without insulating it will double up pretty easy.

And if you plan to use baseboard electrique heaters keep them to the exteral walls and watch the circuit rating and also no receptales above the straight electrique heaters { hot water verison is not a issue due it not hot engough }

Merci.
Marc
 
  #12  
Old 09-16-10, 03:41 AM
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Thanks for all the thoughtful responses. I am in Missouri, just south of the kansas city area, so will have some cold days in the winter where restance heat will kick on. Will likely add a wood/corn/pellet stove, but certainly want to have electric backup regardless.

Just so I have this straight in my head, for 100A service, I will need 2 runs of #2/0 aluminum and one insulated #4 (copper?) for a common. I'll connect a 100A breaker at the pole, run my wire, add an 8' ground rod (bonded to common and metal of panel) at the 100A service pannel at the cabin.

Cabin is only 400 sf and will be super insulated.
 

Last edited by clemenm; 09-16-10 at 04:28 AM.
  #13  
Old 09-16-10, 06:12 AM
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With the breaker at at your meter you will need a 4 wire feeder to the cabin, 2 hots, 1 neutral and 1 ground. The neutrals will be isolated from the grounds.
 
  #14  
Old 09-16-10, 08:27 AM
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Originally Posted by clemenm View Post
I will need 2 runs of #2/0 aluminum and one insulated #4 (copper?) for a common.
(2) #2/0 aluminum hots
(1) #2/0 aluminum neutral wrapped with white tape on both ends. This wire could be reduced down to #1 if you want.
(1) #4 aluminum ground wrapped with green tape on both ends

add an 8' ground rod (bonded to common and metal of panel)
The ground rod connects only to the ground bus in the cabin panel, not the neutral bus. The ground rod must connect with #6 copper, by the way, so you'll need to get a few feet of that.
 
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Old 09-16-10, 08:39 AM
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Don't know if it was said but ground is bonded to the panel and neutral is isolated from the panel and not connected to the ground bar. The panel you buy will probably not include a grounding bar. You will have to buy one and add it to the panel.
 
  #16  
Old 09-16-10, 09:32 AM
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Just got a quote from a local supply house for 2-2-4 aluminum burial at $1.08 oer ft. for 1000' role. Is that what I want?
 
  #17  
Old 09-16-10, 09:37 AM
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No, that only has three wires and size #2 is much smaller than size #2/0.

^^^ smaller
#4
#3
#2
#1
#1/0 (same as #0)
#2/0 (same as #00)
#3/0 (same as #000)
vvv larger

You can buy the cable preassembled (280' of four conductors all twisted together) or you can buy a 1000' roll of just #2/0 conductor and cut it into three 280' pieces yourself and also buy a 280' length of #4. It depends on how your local supplier sells it.
 
  #18  
Old 09-16-10, 04:25 PM
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Thanks very much for the great guidance. I know it takes time and effort to give learned advice to this DIY forum. Very appreciative of the help! Will let you know how ths progresses. Framing begins in two weeks.
 
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Old 09-16-10, 05:24 PM
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2/0 is shorthand for a size of "00". Wires increase in size as the number decreases. Exanples 2 larger then 3 and 1 is larger then 2 and 0 is larger then 1 and 00 (2/0) is larger then 0 and 000 (3/0) is larger then 00 (2/0).
 
  #20  
Old 10-18-10, 04:34 AM
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Plan B?

Well, cabin is framed in and I am revisiting this post to go over the requirements for the install. I am now thinking that I will just go with only the heat pump electric unit and use propane for hot water which will lessen the load and perhaps make this a little less expensive. What amperage service (60?) would the forum recommend with only the heat pump/resistance unit and lighting (I am adding a wood stove so I doubt very much use on the resistance heat source)...and then what guage aluminum conductors to install? - Matt
 
  #21  
Old 10-18-10, 08:11 AM
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You could do a 60A service with a four-conductor #2 aluminum cable. This is a really common size so you would be looking for something like #2-2-2-6 or #2-2-4-6 aluminum direct burial. It should be type USE-2 (underground service entrance) or MHF (mobile home feeder) or URD (underground residential distribution). It will probably be advertised as a "100A" cable, but in your case it will be perfect for 60A over the long distance.
 
  #22  
Old 11-12-10, 02:40 AM
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Okay, got the cable installed (it is 2,2,2,4) and now ready to make my connections. I am a little confused regarding the separate ground for the #6 wire. Here is what is in the pannel: Connections for two hots, the nuetral and a ground bar. The ground bar does not have a large enough receptical for the number 4 wire from the pole. I assume I can get an adapter to make this connection. I bought a separate ground bar for the pannel. It has two screws that will attach to the pannel for the bond. I then connect my #6 wire to it- correct? Now, as I make my circuit connections inthe pannel, I will not use that ground bar but use the one connected to the 4 wire from the pole grounded connection - is that correct?
 
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Old 11-12-10, 09:02 AM
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Originally Posted by clemenm View Post
The ground bar does not have a large enough receptical for the number 4 wire from the pole. I assume I can get an adapter to make this connection.
Most of the modern brands can take a #4 wire right to the regular screw terminals, it will just barely fit through and you might have to give it a careful twist. If it really won't fit, you can get an add-on "lug kit" to make the connection.

I then connect my #6 wire to it- correct?
The #6 to the ground rods and the #4 from the feeder both connect to the ground bar which is screwed directly into the metal case. You are allowed to have multiple ground bars as long as they are solidly screwed to the metal case if that's how I understand your situation. The bare ground wires from your branch circuits can connect to this bar.
 
  #24  
Old 11-12-10, 11:40 AM
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I think I am following you. Sorry to be so dense on this but I want to get it right...Are you saying the non-case-bonded (isolated) ground bar will not be used at all unless it is attached to the case bonded ground bar? In other words the ground bar that we bond to the case will be connected to both the 4 wire and the 6 wire (grounded on both ends so to speak) is the one we use. If I were to connect the issolated ground bar to the grounded bar then I could use ALL of the capacity from both bars. Have I got it right?
 
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Old 11-12-10, 11:54 AM
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The isolated bar, the one on insulators, is not a ground bar. It is the neutral bar.
 
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