cord reels - dumb question

[rvr6000]

Hey everyone. While I was recoiling the power cord in the garage this morning I was trying to remember back to my highschool physics classes.....isn't there something about having electrical cords wound up that causes them to lose power? Kinda like you would lose water pressure in a would up water hose I guess.

Was just curious what that was called or am I'm just imaging it. Thanks.

 

[mrb]

not loose power, but you can very easily overheat the cord.

 

[nehog]

If tightly coiled, so there is limited air circulation, there is the potential for overheating. This is resistance heating, not (as some think) magnetic. However, to get this heating you need to run the cord at close to its maximum rating, for extended periods of time.

 

[Zrexxer]

More of an issue with welding leads. Having a couple hundred feet of large diameter copper rolled up forms a coil which adds inductance to the circuit and can change the arc characteristics. Plus, the heat is more of an issue with leads since you could have 100 or 200 amps or more of current.

 

[rvr6000]

Thanks all.....for some reason I was thinking it added to overall voltage drop or something. Must have dreamed it.

 

[jimp]

You remembered correctly. A coil (reactor) will store energy and resist a change in current flow, either up or down. Utilities use them to correct phase angle along with capacitors.

As far as your reel goes, it should not be a concern.

It's good to see some people remember high school (ancient history for me).

 

[mrb]

You remembered correctly. A coil (reactor) will store energy and resist a change in current flow, either up or down. Utilities use them to correct phase angle along with capacitors.

As far as your reel goes, it should not be a concern.

It's good to see some people remember high school (ancient history for me).

since the cord contains two conductors with current flowing in opposite directions, the fields cancel each other out and there is no inductance or magnetic field generated.

 

[jimp]

Forgot about that, opps

 

[rvr6000]

Good info....thanks. Funny how strange things like this can just pop into your head after so many years.

 

[bchee]

 

[nehog]

More of an issue with welding leads. Having a couple hundred feet of large diameter single conductor copper rolled up forms a coil which adds inductance ...

There, I fixed it for you...
BTW, take that single conductor welding cable, and managed to drop some steel or iron in the center, and things get much more interesting--the iron core increases the inductance substantially. And AC and DC welding would react differently too... When doing DC welding and you stick a bit of steel into the coiled (single) wire, you will magnetize the steel nicely!

 

[z28toz06]

Now that you mention the water hose thing, is that true? Do they really lose pressure when coiled?

yes it does, kind of like going around a corner in a car, it increases resistance. We have TDR's at work for measuring metalic cable lengths. when you are measuring cable still on the reel, you have to allow for + 2% to the length for accuracy. we also have O-TDR'S for optical cable (fiber optics)

A TDR IS A time domain reflectometer, which sends a resistance calibrated signal or electrical impulse along the cable. when it hits the other end it bounces back. the amount of time is calculated and turned in to an amazingly accurate footage readout.

http://en.wikipedia.org/wiki/Time-domain_reflectometer#Description