Need info on long run.

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Old 10-04-09, 11:30 AM
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Need info on long run.

I am looking to run power from the main house up the mountain about 400 feet to a small cabin.
I am only wanting to run a few lights and a laptop off of the supply so there won't be a huge load. I have checked out direct burial #6 wire and it is way more than I had anticipated at almost $2,000 locally. I guess I'm just looking for opinions on whether I could safley go with a smaller (and less expensive) wire.
Any info would be great, thanks.
 
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Old 10-04-09, 12:10 PM
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Here's the link to an on-line voltage drop calculator so you can go ahead and figure several different combinations of voltage and load.

http://www.elec-toolbox.com/calculators/voltdrop.htm

One thing that you could do, although I don't recommend it, is to use a pair of transformers to first step-up the voltage to 480 for transmission and then step-down for usage. New price for a transformer of 1,000 VA capacity is about $275. but you may be able to find them at surplus for much less. A pair of 1,000 VA transformers would give you about 8 amps maximum at 120 volts and that should be enough for a laptop and a few lights. The biggest problem is that once you have some electricity available the tendency is to want to use more than the system will supply.
 
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Old 10-04-09, 12:31 PM
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I agree with Furd, the next thing will be a small heater to keep you warm. A fan to keep you cool, and why not put in a TV, then VCR/DVD, satellite, and you may as well have hot water for comfort. Before you know it you are overloaded.
Not sure what your cabin is used for, but it may pay to go ahead and wire it up, put in a panel, meter base and have the POCO heat it up.
 
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Old 10-04-09, 01:14 PM
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The cabin is going to be used as a small getaway for me and a extra place for when guest come. I was planning on having all the usual amenities but not relying on electric for them; propane tankless water heater, gas stove, gravity fed water and fireplace for heat (with electric fan).
This cabin is REALLY far from the street so having a meter put in is probably out of the question, also I'd like to keep this project off the books.
 
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Old 10-04-09, 01:29 PM
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Propane takless water heater.....electric for ignition and computer.
Gas stove....electric for igniter and clock.
Fireplace with fan...electric.
Lights...electric.
Receptacles, whatever you plug in...electric.

Without spending the money on the larger cable, it may not be feasible.
 
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Old 10-04-09, 02:12 PM
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I don't know the price but have you checked direct burial quadplex aluminum mobile home cable?
 
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Old 10-04-09, 02:43 PM
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#1 aluminum Mobile Home feeder would give you 30 amperes at 240 volts. That's 4, 15 ampere circuits.
 
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Old 10-04-09, 02:46 PM
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Be sure to check out an electrical supply store for your wire. They are almost always cheaper than the big box.
 
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Old 10-04-09, 04:00 PM
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Have you considered a 12 volt solar system to power a few lights and laptop? Anything more and I really think you need to consider having POCO put in a service drop.
 
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Old 10-04-09, 05:08 PM
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I like the idea of solar but the geography of the area wont allow it. I'm gonna check out the mobile home feeder cable and see if that is less expensive. Is there a downside to using this kind of cable?
 
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Old 10-04-09, 05:33 PM
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Tell you what, I'll sell you my Yamaha generator for $1500. It's rated at 2800 watts continuous / 3000 watts for 20 minutes and it has less than eight hours run time on it. It works fine at keeping my furnace, television, DVD, computer, refrigerator and a few lights on when my power goes out.

Of course you will have to drive to Seattle and pick it up.

(Yes, I'm kidding.)
 
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Old 10-05-09, 10:00 AM
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Jimbo,

I echo the above comments about electricity usage. An essential first step is to figure out in detail how much electricity you will be using. A laptop plus a couple of CFLs is a rather different situation than a laptop, an external hard disk, a desk lamp, an overhead light, a small fridge, .... You _can_ do this rather inexpensively, but you will get very limited capacity. If you squeeze the design too much, then you will end up having to re-do the whole thing.

As the saying goes: If you don't have the time to do it right, when will you have the time to do it over?

With that said, the other have of the first design step is to figure out how much voltage drop you can tolerate. Code does not have an explicit voltage drop requirement; simply a recommendation. This is what is known as a 'design decision'. If you arrange other aspects of the design so that you can tolerate large voltage drop with acceptable performance, then code doesn't require you to keep the voltage drop low.

For example, most laptops have universal power supplies, that will happily function with a supply voltage of below 100V. If your only load were the laptop, then your installation could tolerate a 15% voltage drop and have acceptable performance.

Incandescent lamps will simply get dimmer and less efficient with reduced supply voltage; if the light from a 120V bulb operating at 100V is acceptable to you, then it is entirely acceptable to have an installation where the voltage drops to 100V.

Some LED lamps are actually designed to regulate their output for different supply voltages, and could tolerate lots of voltage drop with perfect functionality.

On the other hand, motors are very sensitive to voltage drop, especially in starting where they draw lots of current. Depending upon the mechanical load on the motor, this could mean a motor that starts slowly but runs acceptably...or it could mean a motor that fails to start, overloads, and burns out.

So you would need to examine the items that you want to power, in order to figure out how much power you need, and how much voltage drop you can accept.

The other thing that you need to consider is the total cost picture. You've mentioned the cost of the wire...but you also have to stick the wire into the ground. How much will this cost? Remember that there are minimum depth requirements, as well as other requirements. Will you run conduit, or are you going to use direct bury cable? Etc. If you are paying $1K for the trench, it makes little sense to try to save a few pennies on the wire. One of the reasons that people are recommending going with the larger wire is that as part of the total cost picture you end up paying only a few % more for much better performance. On the other hand, if you are willing to do the labor (time cost but no dollar cost) and have the extra time but not the extra cash, then the wire becomes a much larger fraction of the cost, and it makes sense to minimize this expense.

In your situation, I might consider using 12-3 UF cable, direct buried. This would let you supply almost 2700W (at 240V)with a reasonable 3% voltage drop, or 625W at 120V with the same 3% drop. (You did say 400 feet, right??). In theory you could run a laptop and a couple of CFLs with just a single run of 14-2 UF...but using x-3 allows for 4x the power (by allowing 240V), and 12ga is only slightly more expensive than 14ga.

-Jon
 
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Old 10-05-09, 12:29 PM
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One additional note. You should be checking for the bulk price on a 500' spool of whatever cable you buy. Bulk rate is usually lower than per foot price. You can order 500' rolls from many different places on the internet and have it shipped freight for maybe $50 extra which may save you a lot over the local price.

Furthermore the price quoted in your original post is way above market price for #6/3g UF-B. You shouldn't be paying more than maybe $2.50/ft ($1000) if you decide to stick with the #6 copper. Look for a new supplier.

I also agree with Winnie's post about getting by with a smaller cable. If you install 10/3g UF-B or 12/3g UF-B with a 20A double-pole GFCI breaker you get two circuits and burial depth is only 12". If you go with the larger cable and a subpanel burial depth is 24" which may be much more difficult given your soil conditions.

If you're trenching for a water line you could put an HDPE duct in the hole as an electrical conduit to pull individual conductors which would allow future upgrade if necessary.
 
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