Ground Fault circuit protection question

Discussion in 'Shop Talk' started by Randy Rooster, Dec 3, 2006.

  1. Randy Rooster

    Randy Rooster Well-Known Member Supporter

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    I have gfci outlets in my shop, but I need to run about 300 feet of extension cord to the sight where I am building my house. Does the gfci in the wall outlet give me protection with that length of cord or should I buy a 20 dollar plug in gfci like I saw at lowes and put it on the end of the cord where I plug in my tools?
     
  2. suburbanite

    suburbanite Well-Known Member

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    A gfci will protect all devices 'downstream' from the gfci. If the gfci tests as good (they do wear out over time), then you should be fine with the long extension cord.
     

  3. countrymech

    countrymech Well-Known Member

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    First of all, what kind of load are you expecting to handle through 300 ft of extension cord? Is this cord 14Ga, 12Ga, or 10Ga? What size breaker is your circuit on? The reason that I ask is because eextension cords induce a great deal of resistance to the electricity and therefore equate to more draw on the circuit. My hunch would be that a 300 ft run of #14 cord would trip a 20 amp GFI after a couple minutes of run time. I say this because that I have learned the hard way over the years with trough de-icers, heat lamps, Mitre saws and grinders. Same thing always happens, POP!!! I would suggest run #10 at least and if you are worried about GFI protection, the buy a 20 amp and mount next to the jobsite after the extension cord. I have seen them at the Ag store and seen home built units in "Wood" magazine. Personally I would see if I could borrow a generator or trench in the power lines first. Just an opinion, Paul.
     
  4. Explorer

    Explorer Well-Known Member Supporter

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    300 feet is a long way to walk to reset the GFI. When I was building my barn I made a three leg extension cord. Bought two 100' cords and cut them at 50'. Then a junction box, with three cords coming out and installed a GFI breaker (not an outlet) in the junction box to connect the three legs. It is very useful in different areas or having more than one tool connected.

    I would use #10 wire for the 300' run.
     
  5. tiogacounty

    tiogacounty Well-Known Member

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    The last two posts are correct. you cannot run an extension cord 300' and expect to have workable voltage at the end. Once you drop to the 102-105 volt range, you will be burning up power tools. I know it's going to be expensive, but your best bet is to buy a roll of 10/2 romex and make a temporary cord out of it. For protection at the tools, there are ground fault devices available that are molded into a 2' cord, They have a resetable, weatherproof breaker built in. We are required to use them at work, regardless of where we plug in. Depending on your situation, it may be cheaper and easier to run a generator.
     
  6. TheBlueOne

    TheBlueOne Well-Known Member

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    For something that will be left outside exposed to the elements until the project is done, Type UF is a safer choice as compared to Type NM (Romex). Type UF is rated for damp locations, Romex is not.
     
  7. cfabe

    cfabe Well-Known Member

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    300feet is quite a ways to run a heavy load. As others have mentioned here the issue is voltage drop. You want to keep under a 5% voltage drop under full load. Do the math yourself if you have an EE degree or use an online calculator like here: http://nooutage.com/vdrop.htm

    For a 15 amp load to be under 5% drop, you will actually need to run 6ga wire. Construction equipment is usually somewhat tolerant of voltage drop, 8ga wire would get you 5.9% drop which would probably be okay. 10ga would be 9.3%, an you would probably start to experience problems at that level. Circular saw stalling out, compressor not starting reliably, etc.
     
  8. cfabe

    cfabe Well-Known Member

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    Another thought... will this house have electric service once it's finished? You could just have a temporary service installed which would serve your needs much better, and shouldn't be too expensive if you're already going to be bringing service to the house.