sub panels to multiple detached structures

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Old 04-14-16, 07:09 AM
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sub panels to multiple detached structures

Hope someone here can point me in the right direction. I have some ideas on how this can be done, but want to see what the "right" way is.

I have two outbuildings on my property - a garage and a small barn. Both have electric service. Each has its own sub-panel which is fed from a sub panel inside the home. The inside sub panel is connected to the main service panel.

The small barn is located roughly 600ft from the main house. The power line is buried in a trench. I don't recall the size, but it was selected to account for voltage drop. The purpose is simply some general lighting - no heavy equipment.

So far, so good.

Now I want to add another small structure (Horse stalls). It will be located about 100 ft from the current small barn and also about 600ft from the house. I am looking for the correct way to add a sub-panel in this new structure.


The current service to the small barn comes up in a PCV conduit outside the structure. The PVC then runs inside to the sub-panel. My initial thought is to install an outside junction box and split the line. One line would run to the existing sub-panel (as it currently does) and a newly added line would run back down into a new trench to the new structure.

While it sounds good, I have no idea is this is safe or advisable.

Another option is to run a new sub-panel off the existing sub-panel. The existing sub-panel is only a 60amp. so I don't think there is much flexibility here.

The remaining option is to run a new line from the house. With a 600ft run, however, that is cost prohibitive. If that's the only option, I will simply learn to live with flashlights in the new structure.

I'm sure I can handle the work myself - as long as I figure out what is the correct procedure. I may consider hiring an electrician for some or all of the work, but would still like to know what the legitimate options are.

Thanks in advance for any direction.
 
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Old 04-14-16, 07:21 AM
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I'd be inclined to add an outside two breaker disconnect box and split the feed to the barn and horse stalls. But do you really need a subpanel at the horse stalls? Are you just needing some lights and may be an outlet? Can you get by with just a simple branch circuit from the barn to the horse stalls?
 
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Old 04-14-16, 07:34 AM
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Good question.

I don't _need_ a sub panel at the new structure. It is only feeding about 6 lightbulbs (and I plan to switch those to LED, so wattage is minimal). Easy enough for one 15amp circuit.

For some reason I have it in my head that you cannot run a branch circuit in this scenario... 100ft underground run to a separate structure. If code allows that, it would be a simpler solution.
 
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Old 04-14-16, 07:49 AM
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I have it in my head that you cannot run a branch circuit in this scenario... 100ft underground run to a separate structure.
It is allowed but I would suggest a 20 amp circuit, most bang for only a few bucks more. If you use a GFCI breaker you will only need to bury one foot.
 
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Old 04-14-16, 07:55 AM
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Thanks for the info. That certainly makes life much easier.

Although 15a would cut it, I agree that 20a makes more sense. I would be running heavier wire anyway to allow for voltage drop.

Thanks much!
 
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Old 04-14-16, 08:18 AM
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Check out Art 547 of the NEC,not sure how it may apply to your situation,as far as bonding etc.
 
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Old 04-14-16, 09:17 AM
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I would be running heavier wire anyway to allow for voltage drop.... 100ft underground run
Probably no need at a hundred feet with just lights but no harm going to #10. You could drop to #12 for the interior runs at the disconnect at the stalls.
 
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Old 04-14-16, 09:32 AM
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@Geochurchi
Thanks for the NEC reference. The light fixtures in use already account for that. I will make sure the disconnect box also complies. I'm not sure how much the dust situation would apply for my application, but I prefer to err on the side of caution.



@ray2047
Good point on the #10. I wouldn't be so concerned about the voltage drop over 100ft, but this run is coming from a sub panel which is already 600ft from the main service panel.

Thanks again.
 
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Old 04-14-16, 11:09 AM
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I wouldn't be so concerned about the voltage drop over 100ft, but this run is coming from a sub panel which is already 600ft from the main service panel.
Voltage drop is cumulative, but only based on the 'last' run. So up-sizing your 100' run doesn't really help you unless you plan on using a 'lot' of power at the horse stalls. Whatever the voltage is at the barn, you'll see very little additional drop using 12ga at 100' at say 5A. And up-sizing to 10GA will only improve it a small fraction.

For example, if the voltage at the barn is say 115v, with 12ga, you're seeing a drop of 1.5v. With 10ga, you'll see a drop of 1.0v. (assuming a 5A load) Not even worth worrying about.

If drop becomes an issue, it's the 600' run that needs to be upsized - but that's another discussion.

(Voltage Drop Calculator)

Although 15a would cut it, I agree that 20a makes more sense.
If one 20A circuit is good enough, go with that. But for the cost of one more wire, you can use 12/3 UF (or 4 wires in conduit) and get yourself two 20A circuits at the new horse barn. Just something to consider.
 
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Old 04-14-16, 03:39 PM
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Good to know about the voltage drop.

This project is not at my home location, so I am not sure of all the details. I know I have 200 amp service in the main house. I am pretty sure the current run goes to a a 60amp sub panel (although it could be 100a).

Based on information here, I have spoken with my contractor. He is going to dig me a trench and drop in 2-inch conduit to the new stall location. Looks like the actual run will be just under 150ft.

When the original 600ft run was made, I know the electrician upsized the wire to account for voltage drop. Since I don't have access to the property at the moment, I can't check on the wire size. I do recall it was some pretty thick aluminum cable... #2 comes to mind, but I wouldn't swear by it..

Based on the calculator linked to, IF I have #2 cable it looks like the voltage drop would bring things down to about 111 volts. Last time I measured, I'm sure the voltmeter showed more than that. In other words I should be fine with 12AWG cable for the new run (although I still may go 10AWG just for the heck of it).

I am confident that a single 20a is more than enough for the branch circuit. There are two lights for stalls, one LED "shop light" in the storage area and two halogen spotlights on the outside (which may be changed to LED). It also has a GFI outlet because it originally housed the sub panel at the end of the 600ft run. (This smaller barn is being moved to accommodate a larger barn in its original location).

The only purpose of electric in this smaller barn is basic lighting. It gets very dark in the country and can be almost impossible to check on horses using a flashlight.


Part two of my dilemma might be the 600ft cable.

Right now, the service entrance runs to the "side" of the current structure (the small one that is being moved). That will be the "front" of the new structure. Because of the way the doors open on the new structure, I may have to move the service entrance. Not a big deal, except the cable may be a few feet short for what I need to do

Digging up a 600 ft trench and replacing the entire cable seems like overkill. I am looking at my options for a splice or an outdoor junction box. I am not sure if the entire underground run of cable is in a conduit, or just the section where it comes up from the ground. If code allows for the no conduit scenario, that is likely what the electrician did.

Any preferences on how to extend that existing (likely #2) cable an extra 6-8 feet? Should I do an underground splice with one of the heat-shrink sleeves? Should I have an above ground junction box?

I have attached a diagram that may explain things better.Name:  wiring_diagram.jpg
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FYI - rough drawing. The "new line" being run to the disconnect would come of a branch circuit in the sub panel. The drawing incorrectly makes it appear that line would be run from the service connection.
 
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