extension cords, sjtw ratings, amps, and volts

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Yowsers

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I don't know if the power supply forum is where this should be, so if a mod could move it to where it would be that would be great.

I bought a few extension cords at Fry's the other day and I asked a sales associate what type would be best for computers (by type I mean there were 12/3 SJTW, 16/3 SJTW, etc). My question is, what does this mean?

I read:

Extension cords - talks about gauges (AWG) briefly.
Wikipedia - american wire gauge - description of AWG

After all this I still haven't found a simple explanation to the numbers I have been receiving on the packaging of the extension cords.

It reads "16/3 medium duty"... and I bought another that says "12/3 heavy duty". My assumption is this... the 16 is the gauge... and the 3 is the 3prongs... make sense?

So my next question, is on the package for the 16/3 it says 13A (i believe this is 13 amps) - 125V - 1625W. So that this particular cord, 16/3 medium duty, is rated at 13amps * 125V = 1625 total wattage allowed on it? Does this seem correct?

If so, where on earth does it say this on the cord itself? The 13a 125v 1625W is on the packaging, but it is not printed on the cord anywhere. The only aspect that is on the cord is the 16/3... does this mean that I can roughly calculate the wattage of this cord by looking up the gauge 16 at wikipedia which is 10A and multiply by 125V to get roughly 1250W able to run on that cord?

If this doesn't make any sense please let me know and I will try and rephrase :) Thanks!
 
Exactly correct. (3 wires not prongs but I nitpick, same thing really in practical terms)

One thing I keep in mind is that the typical outlet in the wall (unless it is the kitchen which by code requires 12Ga wire and a 20A breaker because it is assumed people will be plugging in high wattage devices like toasters) is wired with 14GA wire and is on a 15A breaker if you are in the USA.

The length should also be considered, the smaller guage wire (higher guage number) has more resistance so an 100 foot extension cord of 18ga wire is not a good idea.

16guage is decent size and quality for a short (25ft) run and the 12ga is excellent for longer runs or a heavy load as it is bigger wire than what is in the wall.

Sound like you got a couple of decent cords. The old school way is to plug em in and running whatever you are running full blast, grab the cord, the cord should maybe be just barely warm or warm to touch. If it is noticeably warm or anywhere near very warm or hot, get a cord with bigger wire inside.


Disclaimer: Somewhat of a simplification, you have to watch for how the max amperage of a wire is rated, many times it is in "free air" which because of the cooling effect of air, the current rating is much higher than "in conduit" or "enclosed" . The wires in the extension cord are bundled together (reduces amperage capacity due to the close proximity of the other wires) and enclosed in an outer protective cover/insulator (another amperage derating) as that tends to hold in the heat. However the amperage values the OP used are reasonable so wherever he found them seems to have taken into account the actual wire application. The amperage rating is an awfull lot about getting rid of the heat generated by the wires resistance to current flow. Just like our CPUs you can put a fan on a wire rated for a modest amount of current and by efficiently removing the heat, the wire will carry a lot more.
 
cool thanks!

I reread your message and did you say that my assumption was correct... in the sense that 16/3 is 16 gauge / 3 wires ? So I could just use the chart on that wiki page to get the Amps of a 16 gauge wire and figure out the wattage it should be able to carry?
 
Copper wire
current rating
with 60 °C raceway
Click to expand...


the values I saw listed 20A for 12 gauge 15A for 14 gauge and 10A for 16 guage seem reasonable, so yes, IF there is no other information availble.

But as you mentioned and correctly calculated if there are marking on the wire or on the package you should go with that.

So my next question, is on the package for the 16/3 it says 13A (i believe this is 13 amps) - 125V - 1625W. So that this particular cord, 16/3 medium duty, is rated at 13amps * 125V = 1625 total wattage allowed on it?
Click to expand...

exactly right, but note the package gives 13A and the link says 10A. If this is for something important, brushing aside the issue of an extension cord on something important, I would not load the cord beyond 90% of it rating however you determine it to be. Your call. At worst you will trip a breaker somewhere.
 
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