voltage drop for extension cords

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I bought some nice 12 guage extension cords which are rated at 15 amp and 1875 watts. They are 100 feet long and run 15 amps great and I don't feel the cords getting warm at all. Except I used a voltage drop chart to calculate voltage drop and it drops 4.76 volts which is 3.96% Why do they rate the cords at 15 amps if the voltage drop is so much? Or is this fine? I thought you're supposed to stay under 3 percent? This doesn't make sense since 12 gauge wire is good for 20 amps. I got 100 foot cords cause I'd rather have too long a cord than too short. I run power tools off these cords like table saws, miter saws etc. The tools run good as far as I can tell
 
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You can still run 15 amps through them, your voltage just varies due to the resistance in the wire. Your power tools should be fine between 110-120 volts. Your tools probably aren't drawing the full 15 amps anyway. This is why you're better off using a cord that's just long enough for what you need and not running an extra long cord.
 
Get a 40 pound cat litter bucket, or a 5 gallon bucket.

Cut a 2 inch hole in the side, at the bottom. Run the male end out the hole, about 12-18 inches...

Coil up remaining extension cord in bucket.

To use, put bucket by outlet. Plug male end in socket. Uncoil what is needed, re-coil when finished.

Saw this on a home improvement show...
 
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There is so much thermal mass and surface area there, I don't think you would feel them warm up regardless.

You have a point - in big homes, 20A circuits may be run with 12ga wire for very lomg runs, say from one end of a home to another, basement to attic. May not be 100ft, but sure has to be close.

Consistency of loads must be factored I guess. The NEC has at least two tables to account for ampacity in conductors for home use, based upon status as a feeder or something else. I suppose that an extension cord may have a few things going:

-stranded vs solid wire
-assumption of load consistency/average loading
- assumption of fault protection or lack thereof
-assumption of voltage drop in wiring prior to cord

Etc.

As was mentioned above, I'd want as short as practically possible, in as heavy a gauge all the time, to ensure minimal drop at all times. Lower voltage means higher current for any load where a constant power can be provided. Ohms law. So I'd not want to injure equipment unnecessarily by introducing more voltage drop than is absolutely necessary.

Interesting question.
 
I think you are overanalyzing the situation.
Assuming you bought the cords that were manufactured marketted and sold to you at a retail store, you can have some faith that they were designed to perform as rated and conform to best practices and code. Especially given the litigous nature in the US.

So its fine. Nobody is going to sell you a 100ft extension cord that actually just on specs is inherently flawed and won't even work and will cause a fire and burn your house down
 
Sure you want as low a voltage drop as possible, but by no means is 3% some kind of gold standard.

Most anything you will connect to it will happily tolerate a 10% voltage drop without any performance issues.

As an above poster mentioned, there is too much mass and surface area of the wire (that will dissipate heat) for it to get hot.

In the 100ft instance, it's the length of wire creating the resistance. That extra wire helps dissipate heat. Where heat comes into play, is forcing too much current through too small a conductor, which also has the effect of increasing resistance, and inducing voltage drop.
 
12 ga. wire rated 15a/1875w b/c of the 15a rated male/female ac ends. If you were to make up your own cord using either SJOOW or SOOW 12ga. wire w/20a. rated connectors, then assume it would be a true 20a extension cord?
 
What is your house wired with? It does no good to use a long 12g extension cord if the outlet is wired with 14g from the box.
 
Originally Posted By: SHOZ
Most houses are running above 115V. I am around 125V.


I checked a couple outlets and im at around 122.5v so that puts me around 118 volts. Should be good then. I need to check the place I keep my tools and see what it says.
 
I would not have a one size fits all 100' 12 ga. extension. You are bound to get voltage drop. And when your Skilsaw hits some really hard wood and draws more amps then the voltage drop will be even more.
 
Well, when you hear and feel the skilsaws motor pull down because of really hard wood you back off the feed pressure to keep the rpm's up because otherwise you are probably exceeding the designed amperage rating of the tool!
 
NEC limits voltage drop to 5%. An engineer has the discretion of how to divy up that 5% drop. That 5% is from the main service connection (usually your panel) to the final device. If there is less than 1% voltage drop to the receptacle you are plugging into, you still have 4%+ left to drop over the extension cord.

Also, if your devices are rated at 110V, they'll handle the voltage drop better than ones rated at 115V or 120V.

Also by code, 20A circuits must use a minimum of #12 AWG. Anything above 20A up to 30A, must be #10 AWG minimum.
 
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Originally Posted By: spasm3
What is your house wired with? It does no good to use a long 12g extension cord if the outlet is wired with 14g from the box.


Hogwash. The issue here is increasing the overall length of the conductor. You could have 5ft of 14 awg, or 50 ft of it leading up,to the outlet. Then a short or long extension. Because of the resistance, higher ampacity means heavier gauge in the overall circuit to ensure less total voltage drop. A shorter run can always get away with a smaller conductor in extension duty.
 
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