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10 vs 14 guage extension cord - hype or help

Post in 'The Gear' started by precaud, May 3, 2008.

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  1. precaud

    precaud Minister of Fire

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    As a user of an electric chainsaw and splitter, I've read with interest the many opinions expressed here and elsewhere about the virtual necessity to use 10 guage extension cord for anything 50 feet and longer, in order to mimimize power losses. So I decided to do a test to see if it really does make a difference.

    For the past two years I've used a 75 foot 14 guage extension cord that I built using better components than the store-bought stuff, and it's worked fine. I didn't really want to go plunk down over a hundred bucks just to do this experiment (10/3 goes for over $1.50 a foot here). Luckily, last week I found four pieces, 70 feet total, of neoprene-jacketed 10/3 in amongst the mounds of electronic surplus in my warehouse. This morning I spliced them together with tinned copper wire splices, crimped and soldered all the joints to minimize contact resistance loss, and double heatshrinked the unions for durability.

    From the charts, 75 feet of #14 has a resistance of 0.180 ohms, and 70 feet of #10 has a resistance of 0.071 ohms, a factor of about 2.5 difference. On the face of it, those numbers don't sound high enough to be significant. But the total AC loop resistance is actually 0.360 and 0.142 ohms respectively. And those numbers are getting high enough where their difference might be influential in a 15-amp draw situation. The question is - is it noticeable in use?

    By the way, I'm not concerned about voltage drop across the wire, it's the current loss through the resistance that would be the bigger power loss.

    I'll be testing it this weekend with a 15 amp splitter (Task Force) and 13 amp saw (Makita UC4000). Stay tuned for results.

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  2. Jerry_NJ

    Jerry_NJ Minister of Fire

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    Your numbers suggest at 15 amps voltage drops of 5.4v verses 2.13v or about 3v more with 14 gauge. This isn't as much as one can expect this much variation on line voltage delivered to your distribution/fuse box, I believe. Your data tells me 14 gauge is fine. As for your "current loss" concern, I assume you mean less current at the device due to the overall impedance in the circuit. Either voltage or current % gives you a measure of your power loss as the "power" delivered to/by your device is Current times Voltage times PowerFactor (not a pure resistive load). So, I stand by my reaction, 3v isn't significant.
  3. raybonz

    raybonz Minister of Fire

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    Voltage drop is what you need to be concerned about... The low voltage is what destroys motor driven tools.. Here is a link for a simple explanation: http://en.wikipedia.org/wiki/Voltage_drop

    Ray
  4. Jerry_NJ

    Jerry_NJ Minister of Fire

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    May I take your long term use of an electric log splitter testimony to how well they work? I see such around, usually called 5 tons of force, for about $300, I also see a two handled manual pump splitter that sells for $100-$150, and has caught my interest. I did post a question on that type splitter and got one user's report that it works.
  5. sylvestermcmonkey

    sylvestermcmonkey Member

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    No current is lost "through the resistance" at all. Current through resistance results in voltage loss (Ohm's law). You're right in that the power loss in your conductors isn't significant from an energy standpoint, the problem is that when your electric motor loads see less voltage, they draw more current. This requires additional heat dissipation in the equipment, which it may not be designed to tolerate. Subjecting motor windings to higher temperatures leads to shorter service life. That's the reason for fatter extension cords.

    It may not be "hype" but it's an oversimplification to say you need a certain conductor size for anything greater than some number of feet. A 2% voltage drop, or less, at the load is considered acceptable. You need to size your conductors appropriately. 10 AWG may or may not be appropriate.
  6. sylvestermcmonkey

    sylvestermcmonkey Member

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    By the way a quick calculation of your homebrew 10 ga 75 foot cable would result in a 2.4% voltage drop under a 15A load. Perfectly fine.

    The same load with a 75 foot 14 ga cable would be more than 6%. Not good!

    Remember that electric motors draw much more current when starting. The inrush current may be much more than 15A. When the voltage drop becomes excessive, your motor won't even start.
  7. precaud

    precaud Minister of Fire

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    Lots of interesting replies but the technical aspects are more of a side show so I won't get into them. I have the equipment to capture the turnon transients (voltatge and current) but that isn't what this is about.

    I didn't haul out the splitter today, so this is based solely on the 13-amp Makita saw. DCR of the UC4000 motor is 0.84 Ohms, and AC impedance at 60 Hz is about the same, well below 1 Ohm. Line voltage here is always nice and high - I've never seen it below 120. Today was quite consistent at 122.6 .

    Voltage drop with the saw on full (no cutting load, and I didn't bother measuring the current draw):
    14 guage : 4.4V
    10 guage : 3.4V

    And how about saw performance? Is it worth it to use 10 guage over the less costly and more widely available 14?

    My answer is, yes, it is. Using a newly-sharpened chain, there is absolutely no question that the saw cut faster and was more powerful in the cut with the 10 guage cord than the 14 guage one.
    Was is night-and-day difference? Not quite.
    Will I ever use the 14 guage cord again for cutting/splitting? Not unless I have to.

    I'd bet that most folks who go out and buy an electric chainsaw are using extension cords that are way too small, and that accounts for much of their impression of the electric saws being gutless.

    And I'd bet it could be made incrementally even better if the 50+ feet of 12 guage romex that runs between the AC outlet and the circuit breaker box was replaced with a larger guage. If I were to install a dedicated circuit out to the woodcutting area, I'd use as large a wire as I could afford. Or maybe run multiple 12 guages in parallel, it may be cheaper to do it that way.

    I'm not going to bother comparing the splitter with the two cords, it's clear what the answer will be.

    Buy the largest guage cord you can afford.

    Hope someone finds this useful.
  8. precaud

    precaud Minister of Fire

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    Jerry, I don't have long-term testimony to offer, I just bought the splitter a month or so ago and have only used it twice. But it performs better than I expected and I'm very happy with it. If you do a search on this site for "task force" you'll see my earlier impressions of it.
  9. downeast

    downeast Guest

    Nice clear explanation guys...great. I have to reach the boat that's 400' from the outdoor box for power. The choice was to use the standard 14 gauge extensions or make one from scatch with 10 gauge. I'll use the latter...thx.
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