Extension cord length charts

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Old 07-26-17, 01:42 PM
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Extension cord length charts

Are extension cord length recommendations found in code, or how are they developed? I ask because I own two different electric-powered outdoor implements, and the included manuals list different requirements.

My lawnmower (12 amp motor) manual says for a load of 12-15 amps, use a 12 AWG cord for 50 feet, and an extension cord is "not recommended" for 100 feet.

But my electric snowblower (15 amp motor) manual says to use a 14 AWG cord for 50 feet, and 12 AWG for 100 feet, and "not recommended" for over 100 feet.

I have the required cords to safely follow the manufacturer's instructions, that's not my concern. I just think it's strange that there's a "difference of opinion" in the manuals, when voltage drop is a universal thing. And even more interesting is that the smaller motor wants a bigger cord. Both tools were purchased in the past two years, both are from reputable, established electric implement manufacturers, and both are designed for 120V use.
 
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Old 07-26-17, 03:13 PM
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AFAIK, the only code around extension cords deals with them being for temporary use only. I would think the manufacturer would be the best source of information on such for their product.
 
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Old 07-26-17, 05:10 PM
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Flexible cords and cables are covered in Article 400 of the NEC. The extension cord will likely be marked as to the type of cord it is. Common ones are SJOW and SJOOW. The allowable ampacity of these and almost all other cords, with 2 current carrying conductors, is 25 amps for #12, 18 amps for #14, and 13 amps for #16.

The concern of manufactures is not ampacity, but voltage drop. The smaller the wire, the longer the distance, and the higher the load (amps) the greater the voltage drop. Voltage drop can be hard on motors. People notoriously use under sized cords. The manufacture is likely trying to get users to use heaver cords for longer life and better performance. The NEC does not have any requirements to prevent voltage drop, only recommends limiting it to 3% or 5% depending if the circuit is a feeder or a branch circuit.
 

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Old 07-26-17, 05:44 PM
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The NEC does have any requirements to prevent voltage drop, only recommends limiting it to 3% or 5% depending if the circuit is a feeder or a branch circuit.
Did you mean to write the NEC does NOT have any ...?

I see this far too often, a responder will omit a very important word that changes the answer to something that makes no sense. Proofreading your responses is not time wasted.

Also, while I agree with Tolyn that voltage drop is the primary concern a secondary concern is overheating the cable. Since a snowblower would not be used in warmer weather perhaps the manufacturer (watch that last "r") thinks, erroneously in my opinion, that a smaller conductor size is acceptable.
 
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Old 07-26-17, 10:33 PM
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Interesting theory on the cord overheating, Furd. The snow blower manufacturer makes lawn mowers too. I just went and checked one of their manuals online, and a 13 amp mower has the same recommendation as the snowblower - 14 AWG to 50 feet, 12 AWG to 100 feet. So at least they seem to be consistent within their products.

Since there's no set standard, I think perhaps the companies are trying to decide how much voltage drop is acceptable for their equipment. Maybe one company says anything under 5% is good, and the other wants under 3%.

Thanks for indulging my curiosity, everyone!
 
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Old 07-26-17, 11:12 PM
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It would be pretty easy to test the mower voltage with the chosen cord stretched out and the mower running. Use a triple plug adapter at the mower and plug a multimer in to one receptacle and the mower in another.

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Old 07-27-17, 08:11 PM
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perhaps the companies are trying to decide how much voltage drop is acceptable for their equipment.
The other thing to consider is manufacturerrrrs (extra r's for good measure) do not know how long the branch circuit is from the panel to the receptacle. You could easily add another 50' - 100' to that length. Really the bottom line is use the shortest cord to get where you need, and the heaviest you can afford. (up to #12, let's not get crazy )
 
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Old 07-27-17, 10:10 PM
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I was going to see about making my own cord with some 4/0 SE cable, just to be safe.

Ray had a good suggestion too. I may give that a try at some point, just for curiosity's sake.
 
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Old 07-27-17, 11:36 PM
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I was going to see about making my own cord with some 4/0 SE cable, just to be safe.
I suspect that is written with your tongue firmly planted in your cheek but I will point out that you will never get the 4/0 to fit into any standard (NEMA 5-15) plug or receptacle.

Really the bottom line is use the shortest cord to get where you need, and the heaviest you can afford. (up to #12, let's not get crazy)
I completely agree that the shortest and largest cord is the best answer. I disagree that using a #10 extension cord is crazy if it is needed.

I DO have a fifty foot #10 extension cord, well, my sister's kid has it right now, but I made it up to use with high-amperage tools. One such is my electric yard waste shredder that takes about 14 amperes (or more) when working. The kid has it for use with my yard blower/vacuum which is also rated at about 12 amperes.

A little story. Back when we still managed the historical museum the director bought a very nice, high powered vacuum cleaner. She used it with a 100 foot #16 extension cord, plugged into circuits wired with #14 conductors although more often than not the fuses were 20 ampere. She ended up burning out the motor and when she found out the high cost of replacing the motor she swore off ever spending large amounts of money for a silly little vacuum cleaner. She also used MULTIPLE #16 and #14 cords to reach out a couple of hundred feet for a string trimmer to cut back the grass at the fence line. The string trimmers died as well and she blamed it on them being electric and from then on she bought gasoline-powered trimmers. I told her that it was the insanely too-small extension cords that did the damage and then made up several #12 cords along with destroying all the #16 and #14 extension cords in the place.

Just because the tool runs does NOT mean the extension cord is adequate. It really DOES make a difference.
 
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Old 07-28-17, 03:56 AM
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I also have a #10 extension cord that I used to use frequently. Painting, especially new construction there isn't always a guarantee that power will be close by. The specs for my airless say not to use over 100' of #12 but many times I've had to use up to 200' [#10 & #12] and I've never had any issues with the motor. I've had to rebuild the pump multiple times but the motor always worked fine. I've know other painters that used #16 and after a few years the motor would quit.
 
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Old 07-28-17, 03:18 PM
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Yes, completely tongue in cheek.

As I mentioned earlier, my cords meet (or exceed) the manufacturerererer's recommendations for these implements. It was mostly curiosity as to where these numbers come from, since there are so many variables that could affect them.

Like Furd points out, how many people read the manual anyway, and if they do, do they really understand what the terms (AWG, etc.) mean anyway? Or do they just go to the Big Box Store and grab the longest, cheapest cord they can find, and then wonder why stuff burns out or catches fire?
 
 

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