drop cord length

I've heard that there is a limited to the distance that a drop cord for power equipment can be used. Beyond that limit there is risk to damage the equipment being used. If this is true, what is this length? My guess is that it depends on the rating of the drop cord. Is there a source where I can determine what size cord is safe at what distance?
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If you google resistance of copper wire you will find tables that give the resistance of wire per foot for each gauge of wire. Then you can use ohms law to calculate the voltage drop. Let's say the wire has a resistance of .01 ohms/ft. Then 100 feet would have a resistance of 1 ohm. And if the load on it is 5 amps, then it will have a voltage drop of 5 volts. So, if you started out with 120v at the receptacle, you have only 115V at the end of the cord.
The rest is up to what the load is, do you really have 120V at the receptacle, and how lucky you feel. As a rough guide, you can use the rule of thumb for residential wiring. 14 gauge for 15 amps, 12 gauge for 20.
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How about X2 , 200 feet round trip. ??
Greg

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Doh! I left them electrons piling up there, didn't I?
You are correct. I only accounted for the voltage drop on one length of wire, so it's actually 2x that and you only have 110V at the load.

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I do a bunch of stuff, but no harm yet. Run a 100 foot 12 gauge extension cord out of garage, but the garage is fed with 85 foot, 10 gauge wire. Small air conditioner works ok. At camp I ran the air conditioner with 100 foot 14 gauge extension into little trailer from big trailer.
During Xmas I have a 250 foot 18/16 extension to feed small set of lights. Looks like lights without a house in sight.
Greg
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wrote:

The 110 volts at the end of the "drop cord" is only 110 volts if it is connected directly to the panel - otherwize there is voltage drop on the 14 g wires from the panel to the outlet as well,. And tha ASS U ME s you have 120 volts at the panel under load - which is not a given, as you can have voltage drops between the transformer and the panel, which will vary depending on the over-all load on the panel at any given time. - Current voltage on an unloaded branch circuit right now at my house is 13.9 - 114 VAC with the AC not running. and 113.3-113.5 with the AC on. - 100 amp service 300 feet from the transformer. About 222 at the AC unit disconnect 50 feet from the panel on #12 cable.
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On Sat, 21 Jul 2012 03:00:17 -0700 (PDT), Frank Thompson

You get a power loss as the cord gets longer. The larger the draw, the heavier cord you need. Plenty of charts around to guide you, maybe even the instruction book of the equipment
http://www.masterrental.com/extcord.php http://www.homedepot.com/webapp/catalog/servlet/ContentView?pn=Extension_Cords_Reels
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On 7/21/2012 5:00 AM, Frank Thompson wrote:

I have no cite for this, but it has been the rule that I live by for 30 years. For every 100 feet of cord, you are losing 15% of your power. I only use 12 gauge cords.
I burned up a perfectly good rockwell circular saw by using too much extension. I had about 215 feet of extension cord out and after 2 hours of cutting plywood, poof!
Now I never go over 75 feet, but then, I have a generator, so I don't have to.
--
Robert Allison
New Braunfels, TX
  Click to see the full signature.
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On Sat, 21 Jul 2012 07:20:51 -0400, "Don Phillipson"

Actually not comeletely true. A too light cord will get hot. A too LONG cord will develop too much heat too, but not at the connections - the whole cord will dissipate heat - and because it is spread out over 50 or 100 feet you will not notice it.
For a 15 amp circuit, 80% load, you need a 12 guage cord or better for 100 feet. For 50 a 14 will do the job. For 25 a 16 is common.
No such thing as too heavy for a cord for stationary power tools. For handheld tools the last couple of feet need to be light and flexible enough to work with.(so if your saw has a 3 foot whip, you will need a short lighter cord on the end if you are running a number 12.)
Always choose 1 long enough cord over 2 shorter ones as the connectors have higher resistance than a few extra feet of cord.
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i have a friend who had a heavy motor load in hhis yard on a temporary basis.
so he parelled 3 14 gauge cords for the 20 amp running load.
it worked but i would of installed a proper buried 10 gauge direct burial cable with GFCI protection. his temporary project took 3 years.....
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