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electricity 750 ft away!?

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14K views 95 replies 20 participants last post by  needshelp 
#1 ·
Hey so I need to get electricity up to my kid's tree house which is 750 ft away from our house. I was looking into 3, 250 ft. 8-gauge wires to make it work but am not sure if it would work. Will the current stay strong enough to keep some lights lit if it it plugged into a standard outlet 750 feet away? Thanks in advance for any help. Cheers.
 
#2 ·
Someone else can help you with the voltage drop calculations, but I would definitely not be considering just plugging this into an outlet on your house. I would hard-wire it direct into the panel, of course making sure this circuit is GFCI protected. If you want you can always put in a disconnect switch near where it exits the house to shut off power to the tree house when its not in use (or to signal the kids to come in for dinner, haha).

You will need to post what kinda things would be in use in said tree house and what your looking at for total power draw. This will have a big factor in how big the wire will need to be to maintain voltage at that distance. Though in all honesty, it probably isnt a huge deal if there is some minimal voltage drop to a kids tree house, but think about what you might use that circuit for once the kids are gone.
 
#5 ·
That is a decent calculator! Personally a run that long I wouldn't be looking to run anything less than 10 gauge; even if it is just a couple lights. Also, how far is it from the tree house to the main panel, not just to the house?

You could always run a MWBC (Multi-Wire Branch Circuit) with 2 20amp circuits one for lights and one for outlets on 10 gauge wire and that would probably be adequate. Minimal voltage drop with lights and some light-weight appliances (tv, game system, stereo, etc) with out effecting the lights (two separate circuits).
 
#4 ·
I 2nd the idea of a light switch inside and running directly from the circuit panel. Might not even be a bad idea to wire up a couple of light posts along the way off of the same stretch. If you get 250' rolls, you could easily put in 2 and have a safe connection. make sure that the run is GFCI inside of the house.
 
#6 ·
Wow thanks for the quick response guys. What panel are you referring to? I would have no idea how to hard wire it! The total wattage needed would be about 400 I am guesstimating. My wife wants them to be able to hang out up there as much as they want this summer so she can focus on work! HAHA.
 
#10 ·
Wow thanks for the quick response guys. What panel are you referring to? I would have no idea how to hard wire it!
This is the perfect time to call an electrician. Seriously.
This is NOT as simple as it might seem.
 
#7 ·
I don't think running this underground just to plug into an outlet is such a good idea! You never know what else is on the circuit and with that long of a run its best that it has its very own dedicated circuit. The panel we are talking about is your main service panel, where all your house's power is distributed from.

It might be worth talking with a local electrician to help wire this up for you. Alot of times you can save yourself a lot of money by digging the trench yourself (make sure its at the proper depth for the type of wire being used).

Most electricians will not just simply hook up wire that you the homeowner ran and buried, they don't want to be liable for something they didn't run. So before you start purchasing wire and boxes, etc call around and tell them what you are looking to do. This will be a fairly simple job never mind the extreme length of the run....
 
#8 ·
I would run 3 wire UF as a multi wire branch circuit as was mentioned. This gives you two 120-volt circuits, and if the need comes up you could use it as 240volts instead.

About gauge, you can use 8/3 UF, but it going to be expensive. I would not use 12 gauge for the main run, the voltage drop is too high. 10 gauge is a possiblity, but I would try to keep the load under 10 amps on both sides of the circuit. No matter what gauge you choose buy a 1000 foot spool, it'll cost less than buying smaller increments, even though it's more than you need. You can sell the extra 250 feet easily I'm sure. You can change it to 12 gauge once you come up from the ground, to make it easier to wire outlets and fixtures. Most outlets and fixtures are not designed for 8 gauge or 10 gauge wire.

UF is rated for direct burial but the trench needs to be deep enough, 24 inches deep. You will want to rent a trenching machine definitely. You should call Miss Utility or whatever it's called in your areas unless you are absolutely sure there's nothing else buried along the entire path. Where it comes up from the trench you need to have it in conduit, but not for the main length with UF rated cable.

Then you need a 2-pole 20amp breaker and two empty slots in your main circuit breaker panel.

The wire alone is going to cost about $500-$600... plus the trenching machine rental.. and then maybe $100 for assorted other things and the breaker. You are looking at about $750 total in just materials for doing it yourself.
 
#16 · (Edited)
Do not run a low voltage circuit that far (with the transformer back at the house). The effects of voltage drop on 12 or 24 volts are much more severe compared with on 120 or 240 volts.

For a given number of amperes and a given piece of wire you lose the same number of volts, not the same percentage of voltage!

(Voltage drop within the cable equals number of amperes times resistance of the cable, remember it's a round trip.)
 
#18 · (Edited)
If it's for intermittent use, you can run skinny wires out there that would charge batteries, and then the batteries would run a DC-120vac invertor, or just run your stuff on 12vdc.

400w for 8 hrs = 3200 w-h of energy = 270 A-h of charge, at 12v.
For the energy you put into the battery you'll get about 5/8ths back out again.
You charge for 16 hours and then discharge for 8 hr.

The batteries need about 14v at the terminals to charge properly. The voltage drop in the wires isn't important in this case because they are only carrying charging current and this is sort-of a constant current charging, but for safety I wouldn't have more than 60vdc at the sending end (the house).
Depending on the charger you get, you may have to run the two leads to carry charging current and two very skinny sense leads
http://digital.ni.com/public.nsf/allkb/19C456663A415FF4862571D800712302
that monitor the battery voltage at the terminals.

If you have a spreadsheet you can run the cost and energy budget numbers and see if there is a clear winner over running line voltage out there.

Prolly there is no NEC involvement with the battery arrangement.
 
#19 ·
As said above you must install a breaker in your main panel or another panel inside your house. From this breaker you can run UF cable underground to the tree house. Keep in mind you must protect the UF cable when it comes up out of the ground and you MUST have a disconnecting means at the tree house. It must be GFCI protected. A simple snap switch will be just fine. Calculating a 5 amp load you would need #4 at 750 feet. #8 at 3 amps load will work too. This is at 3% max voltage drop.



Note: If you are not familiar with any of my statements you really should call a professional electrician.
 
#20 ·
Hardwiring 120volts is going to set you back a grand at least -maybe quite a bit more. Now let's get realistic. This is for use mainly in the summer. When is sunset? 8:30 to 9PM? Just how late is Mom going to need those kids in the tree? You probably need an hour of light. Get a small solar panel and battery and low voltage lights. Save a lot of money and make Al Gore proud.
 
#22 · (Edited)
Running low battery-charging-only voltage from a battery charger back at the house is not going to work well except for very feeble trickle chargers. Otherwise as the battery charges up, the current draw will vary enough to make the voltage applied to the battery vary all over the map.
 
#23 · (Edited)
Running low battery-charging-only voltage from a battery charger back at the house is not going to work well except for very feeble trickle chargers. Otherwise as the battery charges up, the current draw will vary enough to make the voltage vary all over the map.
I think you're right, for somewhat different reasons.

3200 w-h for 16 hours is 200w, which, at 12v or so, is high current over long wires, which defeats the purpose of going to a low-duty-cycle battery system.
And, a constant current charger is not going to work over about 4Adc because of what the batteries can tolerate. 4A over 16 hrs. is not enough A·h of charge for this application.

For the required amount of energy and peak power to be delivered I guess I'd go with 120vac or higher to minimize copper loss and wire size.

BTW, you might get 6w per sq. ft. of solar panel when the sun is shining, so this would be a panel about 8' on a side.
 
#24 ·
I think this is beyond what the OP is willing to do, but can you run a Buck/boost to compensate for voltage drop? i.e. send out 140v ac on a line and with voltage drop it ends up being 115ac when it gets there?

Isn't this how the power co transmits power over long distances, higher voltage, using something like 17K-34K until it hits the transformer by your home then it is stepped down?
Jamie
 
#27 ·
great help everybody! I think I will talk to a local electrician about everything since I definitely do not want to get hurt doing this. About the solar panels as a few people have mentioned, they seem to be more expensive then doing this project. How much would a battery, inverter, and solar charger cost? And how much juice could I get from it?
 
#28 ·
I have a 400 watt inverter(cost about $50), a trolling motor battery($80),
and a trickle charge soler charger($30) and that powers my battery chargers, a radio, and a small fan most of the day.
If you go this route, you need a deep cell battery.

You may have to deep charge the battery every month or so.
 
#32 ·
How old are these kids? Do we really need to be running line voltage to a tree house? Get some LEDs, put them on a switch and wire them to a motorcycle battery. It will last a very long time on a charge. Every couple weeks you could bring the battery to the house to charge it.
 
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