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Old 09-23-2007, 09:37 AM   #1
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125 amp Subfeed


I would like to install a 125 amp subfeed panel. This panel will be fed by a
200 amp main panel. I need to know what copper wire size ( THNN ) I should use. The run will be around 180 feet long and be bury in the ground in 1 1/2 electrial gray pipe.

Thanks for the help

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Old 09-23-2007, 04:54 PM   #2
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125 amp Subfeed


I assume this is for a detached structure?

I would run three #3 or #2CU with a #8 ground. That's the best I can do with the little information given.

Can you give a few more details about this installation so that we can tell if this advice is accurate.

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Old 09-23-2007, 09:46 PM   #3
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125 amp Subfeed


It would help a bunch if you gave us some idea as to what equipment you intend to operate from this sub-panel....and any possibility of a heavy load tool (arc welder) in the future. The load (current on the feeder) to the sub-panel is critical in determining wire size at that distance. The fact you chose a 125 amp sub-panel makes me think you must have some pretty darn big load stuff.

What is the service to your house is in amps?

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Last edited by Stubbie; 09-24-2007 at 03:55 AM.
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Old 09-23-2007, 10:29 PM   #4
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125 amp Subfeed


First, thanks for what ever help you can give me here.

I run boarding stable for horses and I wish to build a 24 x 24 aircondition breakroom or lounge for my boarders to use. Yes, this will be a detached structure and there will be 17,600 btu aircondition window unit, and a smaller 6,000 btu for a closet that will house some computers and backup stock for vending machines. I will have a couple vending machines ( Coke bottle machine, and a snack machine ). A couple ceiling fans, small micro wave, some lights for to be use at night, and maybe a small refrigerator.

I have three horse barns that are also hookup to this 200 main panel. These
barns pull very little if not any load off the 200 panel in the busy times of the day. I also have a shop/hay and feed storage buildings that pull very little a given time. The shop area would be the biggest pull (when we are welding or using a little electrial power in the shop. All the buildings have 100 to 125 amp subfeeds in each.

If I use two runs of #2 THNN as the hot ones. Can I go down one like a #3 on the netural?

Thanks again for your help.
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Old 09-23-2007, 11:05 PM   #5
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125 amp Subfeed


Ok 200 amps ....so how many buildings total are you feeding out of the main panel including the lounge?

Do you only have one service to the property?

In other words are all these buildings sub fed from the main panel in your house?

Do any demands go up in the winter....space heaters, water heaters for the horse troughs that sort of thing?

Also the 17,600 btu window a/c does it also have a heat function for winter?

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Old 09-23-2007, 11:29 PM   #6
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125 amp Subfeed


A total of four buildings are feeding off the 200 amp main panel. This the only service to the property.

No, the demands do not go up in the winter. We are in Texas (it just doesn't get that cold here ).

Yes, the17,600 btu has a heat function. But the breakroom will be well insulated and I don't think we will use the heat that much here in Texas.

Thanks
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Old 09-24-2007, 12:55 AM   #7
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125 amp Subfeed


Ok I think you we be all right with this extra feeder to the break room from your main panel as I don't see the other buildings as being anything other than lights and receptacles that you plug a few tools into and nothing that cycles on and off.
Inspections are required for this type work so just a heads up. I don't know if your area would require a licensed electrician or not for this project so check this stuff out for piece of mind. Farms can be a different deal than in the cities.
The three things that I see that will be on at one time quite often are the coke machine, and the window a'c's. Just from experience your probably looking at 40 running amps in those three units. They all cycle but maybe not if the a/c's can't keep the room cool. The coke machine should be fine. If it is newer it may have built in gfci but it is most likely required regardless in a breakroom. So check your gfci requirements locally...I'll leave that to you.

Ok the minimum you can run to this 125 amp panel is 60 amps by code. I can explain if you want. I would give it 100 amps and I think this is more than enough for any future expansion. Others here may think less so let the thread develop for a day or two to see what others here may wish to add..

Would by chance feeding this break room from one of the other buildings panels be a closer route to take? I ask this because getting 100 amps to that break room would be a lot cheaper if we can cut down the distance.

We would need to be sure of the size of feeder and overcurrent disconnect amperage in the house panel feeding it for starts.

I'm not much of a fan about playing games for feeding the sub panel inbetween 60 and 100 amps. Looking at it long term 100 amps to me is the best design.

I'll post the wire sizes in my next post after you answer the questions in this one. Probably going to be close or the same as Speedy posted.

There is a lot to this other than wire size so I would really like for you to open another thread so we can discuss all the installation requirements as to safety and methods, size of conduit, neutral and ground seperation at the panel, disconnect requirements... etc... etc...

Btw your going to most likely need a 30 amp circuit for that big window a/c.


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Old 09-24-2007, 07:28 AM   #8
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125 amp Subfeed


Stubbie,

Thanks so far for the info. I could run some additional circuits from some of the horse barns to the breakroom. The only thing about that is it would be alot easier to wire the breakroom from a panel in that room. All the buildings have service running to them by underground ( no hanging wires overhead ).
I started doing this many years ago ( a lot neater I think ). The trouble with this breakroom is it is so far from the 200 main service. The room sits at the end of some of the barns, and they are over 120 foot runs. I could run additional power from some of the other barns, but that would cause me to run some long runs in the upper ceilings of the barns. I already have the 1 1/2 electrial pvc pipe in the ground with a pull string in it.

The #2 wire here is around $1.19 per foot if I buy the whole roll ( 500 ft roll for $595.00 as of today from Lowes ). One other problem I would have if
I buy this roll is. If the runs for the two hot legs are 180 ft. each, and I keep the netural the same size. I would be about 40 ft short from my 500 ft roll. Could I splice a extra 40 ft. safely to makeup the distant up?

I would put a 125 amp breaker in the 200 main and then feed the sub with #2 twice for the hot legs and then run the same size for a netural or go down a little to a #3. The sub would also have a 125 amp main breaker in it as well. The ground size from the 200 main to the 125 subfeed I'm not sure of.

The 17,600 btu big boy I feel will not run that much as I said before that I plan on insulating the room well. Further more I plan on keeping the room cool not cold ( cause I have to pay the electric bill ).

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