Question about running outdoor wiring a long distance

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Old 08-06-08, 03:25 PM
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Question about running outdoor wiring a long distance

I have a shed located in my backyard that is approximately 300ft away from my house. I wanted to run a wire out to the shed to power some lights, a small dorm size refrigerator, and a couple outlets for things like chargers are the such when working. I have a space for a 30 amp breaker that I was going to wire it to at my house. I was also thinking about putting a outlet box half way back to my shed in case I need a quicky plugin for hedge trimming etc.

My question is what size/gauge wire would i need to use to run that distance and not have tons of loss. Is there anything i need to add in such as a booster or anything to provide the least amount of loss?

Sorry for asking such a stupid question but i couldn't find the answer anywhere and didn't find anything while searching. Thanks for any help people can provide.

Fritz
 
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Old 08-06-08, 03:57 PM
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First of all, you cannot use a 30-amp breaker on what you call an "outlet".

300 feet is indeed a long ways to run 120-volt power. The lights and the chargers are no problem, but the refrigerator and the hedge trimmer present heavier loads.

You have several options. You might consider installing a subpanel at the shed and running 240-volt power out there. That would help mitigate loss problems.

The first thing to do is to make a realistic guess as to how many simultaneous amps you will need at the shed, both now and in the forseeable future. Guess high, and your costs go up. Guess low, and you'll end up redoing this whole project later.

Suppose you want to hold line losses down to no more than 5%. Suppose you run one 20-amp circuit. If you think you will sometimes use all 20 amps, then you need #6 copper. If you think you will only use 10 amps, then you can get by with #8 copper.

There are a lot of other requirements, such as cable type, burial depth, cable protection, disconnects, GFCI, etc. So when you get ready to actually do this, either study up or come back and ask more questions.
 
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Old 08-06-08, 08:36 PM
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I guess I don't understand your reasoning that 240 would mean less loss. It would possibly if an item out there ran on 240 and drew less current as a result but running 240 out there still gives you two 120 volt circuits with the same wire loss. True you save one wire as the neutral never handles more than the total load of either circuit and often less. You still would have to use the wire size based on the 120 volt circuit current required, the length of run, and the allowable loss.
 
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Old 08-07-08, 02:15 PM
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Originally Posted by dsc3507 View Post
I guess I don't understand your reasoning that 240 would mean less loss.


Simple, voltage drop is based on current and distance, you cant shorten the distance but you can split the total current on two conductors, thus limiting your voltage drop.

Look at it this way, say you have a 1000 watt load, split that in half with two conductors, now its 500 watts per conductor so the voltage drop decreases.
 
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Old 08-07-08, 07:59 PM
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The 240-volt feeder or circuit saves voltage drop only if there is load on both sides. If the load is perfectly balanced, then no current flows on the neutral and there is no voltage drop for half the circuit, thus reducing the voltage drop in half. Of course, in real life, the load would never be perfectly balanced so the savings will typically be less than half.
 
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Old 08-07-08, 08:36 PM
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I guess I did not make myself clear. My point was that if I have 20A worth of 120 volt load - 1 item, then running 240 would give no gain. I can't split the load of a single large draw 120 volt item.

I have no idea what this guy wants to run I was just pointing that out. It is likely that you would not have a balanced load to such a small activity. If you had a 120 volt air compressor or other high draw item it would be on one side of the line and effectively a acting like a single 120 volt circuit. You still need to size the wire based on this scenario. The fact that you get double the power with less copper in a 240 volt feed is meaningless unless you can split the load effectively.
 
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