125% of 80 is 100. conversely, 80% of 125 is 100.

Same principle, however you remember it.

I know this is a several year old post, but this is especially true with vacuum or pump type functions and doubly so when the device is first starting. A device that is rated 10A may pull a lot more than that while the motor is locked in place trying to overcome the initial static pressure of whatever it is pushing or pulling.

Were you able to find what you needed? Or did you build your own cords?

I knew exactly what I wanted and why (a heater for my wife, and an inconspicuous color for inside the house). But every site I tried refused to heed my search terms and kept offering me “heavy duty” 18 & 16 gauge cords.

Overkill for the length? Maybe. Sometimes overkill is the right answer. I like big margins.

Phase Single
V 120 Volts
K Copper
I 15 amps (say a worm drive)
D 100 feet
VD 3% (NEC requirement)
Load Noncontinuous

If I had to size my wire: 10AWG considering a 3% VD. Any more, and the motor won’t see the required voltage, and it’d have to draw more current (more current, more heat).

I think 10AWG or 12 AWG should be a minimum for 100 ft extension cords. We see those long cords on construction sites. I wouldn’t even purchase 14AWG or unless those were 50 ft long. I mean those are fine at home.

The only other major factor is if they light up when powered. That’s mandatory in my book.

I’m trying to think of what uses 15 amps on the construction site beside a worm drive. A 1 inch rotary hammer corded uses 8.5amps, which is a lot less than anticipated. A shop vac uses 12 amps (which seems standard for vacuums). A cement mixer uses 11-12 amps. I think a coring system (which cores holes in masonry/cement) uses 15 amps. Ah yes, the pipe threader, which is 15 amps for 115/120V, and 8 amps for 230/240V. Air compressors tend to draw a good share of amps.

Welders often ask us to run their own dedicated circuit with a 50amp rated cord.

So if you’re not running that sort of equipment, you can get by without a heavy duty 10 gauge extension cord.

Modern breakers have that forgiveness by design, and the trip is temperature related. So you wind up with a window in which the circuit will briefly surpass it’s rating, and allow for the load to normalize without tripping. Same reason you hear about folks complaining that their breaker tripped, they unplugged stuff and they tried resetting it immediately only to have it trip again and again. Still hot, still trips.

Thanks!

I know one company recommended 20A protection for a 16A-rated load. This might help me remember it for good.

16A is 80% of 20A, and 20A is 125% of 16A.

80% it is. *Sustained* draw on an AC circuit shouldn’t be more than 80% of nominal value. I.e. 12 Amps on a 15 Amps circuit, or 16 Amps on a 20 Amps one.

Minimum safety factor I’ll put on a spec or new circuit for customers is 125% of expected load. So if you’re planning on a circuit that’ll see 15 amps (corded saw+dust collection, or whatever) rating on circuit hardware and protections needs to be at least 18.75 amps.

http://www.chem.cmu.edu/groups/bier/procedure_files/general/powercords.pdf

I’ve done the same. I can save a couple bucks today because i only need to run 12A on this… but then 3 months later I have to run 15A on it. Buy once, cry once,

The 220V AC induction motor circuit in the Powermatic tool that you allude to has both real and reactive power components. I’m sure that Powermatic has added a capacitor to the circuit to improve the startup power factor (induction motor no-load power factor can be as low as 0.2) – but as you say inrush current (to provide the needed magnetic field and get the motor rotating) can be much higher than normal current draw. On old fuse-protected circuits this could be an issue so a slow-blow fuse might be specified. Normal (rather than AFCI and GFCI) home circuit breakers seem to be more forgiving in dealing with short spikes.

Yes, it would be a better idea. I have two of them. If you are running a light load over the wire like a corded drill, then you could just have a 16AWG. But remember that a 50′ cord still has the current run 50′ whether it’s coiled or extended. If you have a heavy current draw motor, i.e. a 15amp table saw or compresser running, it won’t be able to pull the power as well; especially, if you have more than one tool going on the same cord. When I had my table saw going and my buddy was using my ROS on the same cord, it upped the load over 15amps. On a 16AWG, you run the risk of overheating the wire or tool.

Depends on what you’ll use it for, but probably. For my own use, I wouldn’t use a 14 gauge reel for something like that unless it was dedicated to light duty tools. I’d get one with a built-in breaker to ensure it’s not accidentally over-taxed.

I wish we used a better connector that created more positive contact and wasn’t so sensitive to wear or corrosion. Also, they pull out too easily, as we have all seen. I don’t know what a better connector would look like, but those connectors for electric cars chargers can handle hundreds of volts and dozens of amps. Why can’t our household outlets be more like that?

I know changing the standard would cost bejillions and take decades. But still.

That’s definitely not how electricity works. All the resistances in a series circuit sum together, period. The order of resistors (cord segments) in a series circuit (which is how the cords act when feeding a tool at the end) does not matter.

If you had a branch in the middle with another tool hanging off there, yes it would matter and putting the thicker cords upstream of that would be the right idea. But if it’s just a single tool, it does not matter at all. Draw it out, look up Kirchoff’s Current Law, and sit down with Ohm’s Law until you understand it.

Also keep in mind safety recommendations. I don’t remember what they are, but I believe it’s maybe 80%. If that’s the case, try to keep your load below 12A on a 15A circuit, and that’s for a dedicated circuit with nothing else running.