Amp Capacity of Extension Cords

14 gauge wire, when used for house wiring, is rated for 15 amps. The wiring will be connected to a breaker of no more than 15 amps rating.

If your house is wired correctly, that extension cord will get a maximum of 15 amps running through it.

Where it is plugged in to the circuit is irrelevant, once that branch exceeds 15 amps, the breaker will trip, shutting off power.

Or to put it another way, you are asking hypotheticals when the example given is already laden with practical limits, thus rendering an answer on the hypotheticals moot.

I think the ampacity of the extension cord is what is labeled on it.

Practical common sense states that there might be a little bit of volt sag if the wiring run from breaker panel to outlet is rather long compared to the shorter run outlet, yes.

The answer is Yes, but not by much.

Very useful information.

In my home shop, I have a fractional horsepower lathe motor, a chop saw, a table saw, air compressor, drill press, and a host of other small loads that more or less get one-at-a-time operation by me. Not a problem, at least the lathe motor does not overheat, and it runs longer than the others. All of this on a 14 gauge 100' extension cord from a wall outlet (20 A) on the back of the house.

The real problem was when I tried running my air conditioner out there. Oops! She gets the cord hot, runs hot, then shuts down (without burning down my work shed).

Maybe there's a reason the A/C unit comes with a 4' pigtail that is 10 Ga AWG?

If you get a chance, cut that 100 footer into a bunch of 15 footers (or so) and get yourself some replacement cord ends from some hardware store... remember this guy?

First of all, this is a "window" unit A/C. It has a typical three contact plug that normally gets plugged into a wall outlet (one that is rated for the amp draw of the A/C, hopefully), and you are not going to get me to mess up a perfectly good 100 footer to satisfy someone else's crazy ideas.

I will eventually get my shop wired properly, maybe. Maybe with its own meter loop.

It is really a tiny little shop building, more of a wooden storage unit. It would make a splendid fire, if I ever went completely stupid.

"It is really a tiny little shop building, more of a wooden storage unit. It would make a splendid fire, if I ever went completely stupid."

For some reason I'm reminded of a story about Ozzy Osbourne. Apparently, one time when he returned home from a concert tour, he was really drunk/stoned/high/some combination of the above, and after he got home late at night, he went out back and set fire to his chicken coop. A neighbor came by, due to the unexpected bonfire, and when he laid eyes on the scene, all the neighbor had to say was, in traditional British deadpan, "So, I see you're back from the Americas."

There's extension cords, and then there's extension cords.

Bottom line is how many AMPS are you trying to pull/push through that particular cord.

A light bulb and a Skil saw will put vastly different loads on the service cord.

It's no different than trying to push 5 GPM through a 1/2" water pipe and trying to push 50 GPM through that same pipe. It'll take a LOT more power to push 50 GPM through it.

Here's a handy guide:

How to Select the Right Electrical Extension Cord - The Spruce

There is definitely a voltage drop depending on length of run....as the voltage goes down the amperage goes up...the wattage demand of your device is what determines voltage amperage demand.......here is a calculator

http://www.southwire.com/support/voltage-drop-calculator.htm

http://www.ecmweb.com/code-basics/dont-let-voltage-drop-get-your-system-down

Yes , but wattage or current demand of the device will determine what the relationship between amperage and voltage will be, whether you are meeting that demand or not is the issue...but good clarification for general purposes....

To answer both your original question and the re-phrased one... No.

If your house is wired to code, the code takes into account the maximum permitted voltage drop in the circuit based on the amp rating of the circuit in question. So, you can ignore the wiring between the receptacle you plug your extension cord into and the source of power for that receptacle. If to code of course.

In other words, the source is still a Thevenin source, i.e. a potential source with a series resistor, but when wired to code, one may neglect this tiny amount of resistance.

If Rs << Rc (the cord resistance), all the voltage drop up to the load will be on the extension cord.

Yes, but no. The code has limits on the length of wire used to deliver a certain current to a receptacle or a load, this is based on the wire size. If you go beyond the maximum permitted circuit length (this includes both to and from the load by the way) for a given current and wire size combination, you need to increase the wire size to be back in compliance with the code.

I got that, but I was attempting to explain why the danged code is the danged code, and why it is written that way. It is because higher wire gauge numbers have less conductor in them, and therefore have more net resistance per linear distance.

When calculating distance, you are certainly correct on all accounts, by saying, take the distance and double it, and if that is within the length specified for run of that gauge at that load, then you do not have to increase wire gauge on that run. If, however, the double length exceeds the allowable, then code would be violated if one did not increase the wire gauge to the next size that meets the standard.

Yes, depending on the length of the cable.

The current carrying capacity of a conductor is limited by its maximum allowable temperature rise and/or the maximum tolerable voltage drop of the load equipment.

All other things being equal, the shorter the distance to the CPD (Circuit Protective Device), the lower the voltage drop at the load. For example, if you have 50' of #14 in the wall and plug in a 50' #14 extension cord, then depending upon the load current, if the voltage at the wall may is just acceptable, then the voltage at the end of the extension cord will not be.

Substituting a 50' #12 cord set will not increase the current carrying capacity of the circuit, but it will result in a slightly higher (but still unacceptable) voltage at the load.

Things get really dicey when there are a number of daisy chained outlets between the CPD and the outlet where the extension is plugged in, since any poorly made up intermediate connections can be a source of increased voltage drop. Even worse, where #12 wiring is protected by a 20Amp breaker, the time-current characteristics of the breaker will allow enough current through the #14 extension cord to raise its temperature to 250F in approximately 90seconds, long before the breaker would trip.

I think a lot of stuff involving appliance and extension cords just gets fudged in many places. For instance, in the USA, most 120 volt outlets are 15A or 20A. But nothing physically stops you from plugging a 16AWG extension cord (good for maybe 10 to 15A) into a 15 or 20A outlet.

<...gets fudged...> That highlights the beauty of the UK system, where there is a fused plug. To protect a cable of smaller cross-section, one merely fits a smaller-rating fuse, say a 3A instead of a 13A. Upstream of the socket, the house wiring, if it were a 2.5mm² ring-main, is usually protected by a 30A fuse or a 32A breaker, according to the date the installation took place.

Fitting the wrong fuse is always the risk.

Agreed. In that respect, I think the British system is better.

This is OT with respect to your post, but on the topic of extension cords, and important, so I won't mark it OT.

When using an extension cord of the type that is stored wound onto a drum, always ensure it's fully extended (i.e. off the drum) when in use. I ignored this rule once, in my youth, and have known several other people ignore it since. The result (for any appreciable load) is a nasty smell, usually some smoke, and a burnt-out cord.

Quite. No-one likes nasty smells.

No project is entirely fulfilled until one lets the smoke out of it.