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Tool Talk Discussion Forum

Correct question to Google to get wire gauge information

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Stan in Oly, WA

07-14-2020 23:20:43




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I used to believe that if you had to use several extension cords of different sizes, such as a 12 gauge cord and a 16 gauge one, to get from the power source to the work site, you started with the heaviest gauge cord at the power source and continued moving away with progressively smaller gauge cords. Years ago I offered this advice to someone on this site and was told that the order didnít matter---the entire length of the run was equivalent to that length of the smallest sized conductor. Is that clear the way I have stated it? More importantly, is it true? I tried to find information about this using Google, but I was not able to word my question so that the responses directed me to the information I wanted. So, besides answering my previous question, perhaps someone could suggest what I should have asked on Google to get the information I wanted. Thanks.

Stan

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Stephen Newell

07-15-2020 18:27:52




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
For the most part both of you were right. The heavier the cord, the less voltage drop you would have so start with the heavier cord. Over a distance though the drop would be so little difference from one size to the other you wouldn't be able to tell the difference. I used to run small power tools off of extension cords at 150 yards. The saw would drag a bit starting but got the job done.



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Dusty MI

07-15-2020 10:53:14




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 Re: Correct question to Google to get wire gauge inform in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
To me, if you are going to use more than 1 ex-cord and they are different sizes, you string them out heaviest to lightest from where there are stored.

Dusty



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John T

07-15-2020 09:05:47




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
Stan, the way I was taught at NEC Seminars wayyyyyyyyyyy back when I practiced power distribution, was to:

1) Compute the "maximum continuous current"

2) Size the conductors to have a minimum ampacity of 125% of that

3) Provide Overcurrent Protection to protect the wire

4) Compute the line voltage drop (depends on current, wire and distance) and if its excessive upgrade the conductor size.

Voltage drop calculators are all over the net, all you need to know is the current, wire and distance EASY PEASEY

NOTE in a series circuit you can have different components or conductors etc drop voltage, and it makes no difference where they are in the circuit, first last or in the middle. The goal is to minimize wasted line voltage drop so the intended load gets as much as possible so you DO NOT have wasted I Squared R energy and heat losses in the line

If there are different size conductors in the line you would need to compute the voltage drop on each one. The bigger conductors have less per foot while the smaller conductors would have more. Compute each then add them all up piece of cake

Heres as an example ONLY, not the best not the worst, of an online Voltage Drop Calculator

https://www.calculator.net/voltage-drop-calculator.html

John T Long retired and rusty EE so no warranty

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David G

07-15-2020 09:05:30




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
If you have taps along the way, then biggest closer to the source, if only tap on end it does not matter.



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dr sportster

07-15-2020 07:32:19




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
Think of the cord as resisitors in series - it would not matter the order but end up the same resistance. What is readily available on the web is a voltage drop chart -- use that.



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MarkB_MI

07-15-2020 07:23:33




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
OK, first off it does not matter the order in which the cords are connected. The same current travels through each cord, and the voltage drop over each cord is independent of its location in the string. It makes sense to put the lightest cord at the end just to have the most flexible cord closest to your tool, but electrically it doesn't matter.

As for current capacity, there are two things to consider: ampacity and voltage drop. Ampacity is simply the maximum current the cords can handle without melting. In general, 14 gauge cords are good for about 15 amps; 12 gauge for about 20 amps and 10 gauge for about 30. Needless to say, 16 gauge cords are best avoided altogether. However, the connectors on most extension cords limit them to 15 amps, which is why a 10 gauge extension cord will be marked as "15 amps", even though its conductors can handle much more than that.

The second thing to consider regarding current capacity is voltage drop. To get an exact answer, you need to calculate the voltage drop over each cord at the expected current, then add up all the voltage drops and decide whether or not the total drop is acceptable. Most folks aren't going to bother with all that, but that's the only way to get a definitive answer.

A general rule is to use the heaviest, shortest cord possible. Let's say you need a total length of 150' and you have four cords: 2 each 10 gauge 100 ft., a 12 gauge 100 ft and a 12 gauge 50 ft. Using the two 10 gauge cords will give you the maximum ampacity. However, you will get roughly the same voltage drop using one of the 10 gauge cords with the 50 foot 12 gauge cord. And you will get the greatest voltage drop and least ampacity using the two 12 gauge cords.

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Janicholson

07-15-2020 07:22:29




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
I will add that the total resistance of all wires (to and from the source and load) provide resistance and voltage drop. My point is that when assessing the power carrying capacity total resistance is to be factored in, including that of the heavier wire gauge. A barn heater is not affected by 90 volts. but a pump motor drawing the same current may be ruined. The resistance is series, so remember the AC is flowing into the small wire first on its way back to the outlet on 50 % of the total cycle. My sone and I were cutting 4X4 wet treated wood from Menards yesterday, with a 100 foot 14 gauge extension cord. My 27 year old son has used the Skill Worm Drive saw (45 years old) from when he could handle it, and he said" dad the saw is less powerful than it was last year. I said only because of the extension cord. The cord was warm. We needed to cut some of the project parts near the garage, with it plugged in directly to the outlet. He was both happier, and informed about voltage drop. Jim

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Russ from MN

07-15-2020 06:48:12




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
I have always tried to use the heaviest cord first, it seems like the less voltage drop you have at the first cord connection would give you the most voltage at the end of the cords. That is kind of the way a service is wired, right? Heavy wire coming in, then smaller a down to the point of use. Many appliances have cords that are barely big enough, and get warm during use.



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DoubleO7

07-15-2020 06:46:36




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 Re: Correct question to Google to get wire gauge inform in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
Think of the lighter gauge cord as an orifice in a run of water pipe.

No point in having 100 feet of 1 inch pipe and then having a 1/2" pipe on the end.



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jniolon

07-15-2020 04:57:44




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 Re: Correct question to Google to get wire gauge inform in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
here's a pretty good explanation

https://www.thespruce.com/extension-cord-choices-1152867

j



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Tony in SD

07-15-2020 03:47:31




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
Your load should not exceed the smallest rated cord. The order doesnít matter if the entire load is at the end because the loop resistance is the same in any order. If you have a simultaneous load midway, then the larger rated cord should be first to reduce the IR drop.



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ChampagneNBeer

07-15-2020 00:06:36




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 Re: Correct question to Google to get wire gauge information in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
Not sure how to google it, but yes, the smallest wire determines resistance in run, all other things being equal.



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Charles in Aus.

07-14-2020 23:57:31




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 Re: Correct question to Google to get wire gauge inform in reply to Stan in Oly, WA, 07-14-2020 23:20:43  
Stan , in fixed installations rather than extension cords the entire run is rated at that of the smallest gauge wire , so if the segment of lighter gauge wire is not within the requirements for the circuit none of the circuit is deemed adequate . It is called ' Breaking Gauge ' and is frowned upon , at least down here .
I suspect the advice you were given was by someone who had gotten confused with plumbing practices where a large bore pipe is often reduced to a smaller one over distance :) .

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