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Extension Cords Math (comparing losses in gauges 12 and 14)
#1
How much better is gauge 12 from gauge 14 ?

Lets quantify this and take 25ft cord and 110VAC / 1100W / 10A appliance. For simplicity I will consider constant 10A current, this only induces insignificant error to comparison.

Btw. I often look at this table, very useful: https://en.wikipedia.org/wiki/American_wire_gauge

#10 0.999mΩ/ft Loss 0.5V / 5W / 0.5%
#12 1.588mΩ/ft Loss 0.8V / 8W / 0.8%
#14 2.525mΩ/ft Loss 1.3V / 13W / 1.3%
#16 4.016mΩ/ft Loss 2.0V / 20W / 2%

Conclusion: Can you afford loosing 5W/25ft more to heat on gauge 14 cord than you would on gauge 12 cord ? If you cannot, then you really need #12 or even better.


NOTES

I use #14 for my 15A circular saw. Did not plan this setup, had this cord when got the saw. Would it not stall and trip breaker on less-than-dry 4" piece if it had few watts extra? I doubt it.

In my opinion manufacturers of general purpose cords rate maximum current on their power cords down to paranoid levels to lower their liability in case of fire. Some others, never learned from their previous power cord recall and in effort to save a few pennies on copper resulted in yet another massive power cord recall due to fire hazard after 56 out of 2.2M overheated.

If anyone is interested in temperature rise in the conductor, I find this calculator very useful, although it is for calculating neccesary PCB traces for the amount of current, it's easy to reconfigure to use mm as units and substitute wires - for example #14 has 2.08mm2 area, that is 1.44mm wire of square profile. By entering these nubers into calcualtor, you may find out that #14 at 15A will heat up by 3-4 degrees C at ambient 25C regardless of it's length.

Using extension cords beyond specification is ultimately your call. I am not endorsing it, just stating physical facts. Use common sense and math to make an informed decision.
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#2
Thanks Roman, my saws trip the breaker some times too. I will invest in lower gauge chord next one I buy. Just costs more for it though.
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#3
The electrical code limits apply to those cords as far as the rating goes - there are tables for flexible cord and maximum amps for each gauge. (those are the same or very close to it that csa would use to approve the cords) Those are not based on voltage drop, they are based on heating, there are other rules for voltage drop but that really doesn't affect the safety of using the cord, it might affect what is plugged in the end.
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If things weren't meant to be modified, they would not come with wires attached.
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#4
(2016-05-04, 12:53 PM)darrin Wrote: Thanks Roman, my saws trip the breaker some times too.  I will invest in lower gauge chord next one I buy.  Just costs more for it though.

Darrin, IMO it stalls because lumber is not dry. HomeDepot or Lowes don't make effort to dry lumber so buy lumber that is sold as dry or buy 1-2 months in advance and let it sit in garage. For faster drying, run dehumidifier there. Or just a fan blowing at boards for 2-3weeks helps to remove water from wood.

(2016-05-04, 12:53 PM)jon Wrote: The electrical code limits apply to those cords as far as the rating goes - there are tables for flexible cord and maximum amps for each gauge. (those are the same or very close to it that csa would use to approve the cords) Those are not based on voltage drop, they are based on heating, there are other rules for voltage drop but that really doesn't affect the safety of using the cord, it might affect what is plugged in the end.

Thanks Jon. This was more about physics than electrical code, but rules are important too, here is guidance to jacketed cords manufacturers, only found UL: http://www.stayonline.com/reference-circ...acity.aspx

OTOH Microsoft must have had CSA/UL approval and since their cords melted, by logical inference CSA/UL rules are imperfect Huh

Be cautious if cord is warm, disconnect and don't use if getting hot.
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#5
we were just having an interesting conversation at work about the 120/240v power supplies on various stuff and the c13/14 connectors.

connector rated 10A, most are universal power supplies, happy at 120 or 240v input.

say you had a cable rated at 5A and a 5A at 240v load from the device, if you use the same cord to power off 120v all of the sudden you have a 10A load, connector is still in the ratings, power cord is undersized by 2x.

its interesting since this actually came up yesterday when we were running a test, everything seemed fine, got a bit warm as expected, only afterwards we realized wait a sec that test was passing 2x the expected current since it got run at 120v by mistake.
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If things weren't meant to be modified, they would not come with wires attached.
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#6
You run that cable unfolded in open space, right ?

How about in Arizona summer while folded on the reel Smile

CSA/UL take worst case scenario. Dissipating power I calculated in first post does not seem very high. There is a long way in quantities of heat from lukewarm to melting PVC. What gauge has Microsoft used in their cables to end up melting and at what conditions were these cases used, perhaps some of them were even scams fishing for settlement? There is not enough information online, but for a cable to start melting the current must be multitude times higher than rated. One would expect Microsoft after first recall of Xbox cords would built in some current/temperature fuse that could be just half inch piece of resistive wire.
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