Retractable Reel Cord and Heat

[crokett]

I read somewhere that when you use the retractable reel cords you were supposed to pull the cord all the way out so it didn't heat up and risk fire or worse. Is this true? Doesn't pulling the cord all the way out defeat the purpose?

[LinuxRandal]

Basically, YES and YES.

Pulling the cords out DOES defeat the purpose of a cord reel, HOWEVER most people use undersized reels and run tools that draw more current then the wire should regularly run.

[JR]

I use a retractable cord reel, with 12 ga. wire. There doesn't seem to be any problem with heat. It is VERY useful in my shop.

JR

[LCHIEN]

Serious answer

Yes, you should pull out all the cord. The cord heats up from carrying large current and the only way for heat to get out is thru the sides of the cable. If wound up, no heat will flow away since the cable layers next to it are equally hot. this can cause a thermal hot spot.

I am usually cognizant of the load I am running and don't always pull the cable out when running small loads, however, if I do run large loads I will pull it all out or preferebaly use a non-retractable heavy-duty extension cord.

You can call it defeating the purpose to not be able to run it partly coiled. That's true if you think the purpose of a retraction cord or cord winder is to minimize loose cable lying around when in use (e.g. an adjustable length extension cord). But you can't think that way, you have to realize their valid purpose is for the storage of the cable when not in use.

[Thom2]

My understanding is that even a loose extension cord should never be used in a coiled fashion as it presents a fire hazard. Cords should always be completely uncoiled before use and should never be covered. Cord reels amplify the possibility because the coil is sealed in a case that will not allow any cooling of the coil at all.

While I won't say that I practice this 100%, it's always in the back of my mind when using cords. I'm fairly concious of the load demands of the unit I'm using the cord for and will act appropriately. For a ROS or something of that nature, I won't hesitate to leave the cord semi-wound. When it comes to the shop vac or circ, the cord normally gets unwound entirely.

[crokett]

Thx fellas. The physics make sense to me but I also wondered if it was one of those urband legend type things.

Loring, I will start thinking of my cord reel as a storage device only.

[Kristofor]

I would agree if you're looking to run any serious current.

However if you're talking about a 60-100w lightbulb on the end of a reel or something similarly low draw I think there's enough empirical evidence to convince me that I shouldn't worry about it.

[MilDoc]

My pull down is a 12G. The only thing ever run off it is a ROS, palm rounter, pad sander, etc. When I first put it up I left the cord in, ran the tool, pulled the cord out to see if it was hot. never was. Now I just leave it in.

[footprintsinconc]

interesting

you know, i also have a 12ga 100ft cable that is on a manual reel that is open on all sides. i only use one tool at a time. i use to run the ts and shop vac togather, but because of ts burning wood, i have discontinued that. but even when i was running both, the cord didnt feel hot at all. i only checked it the first time only to see if the cord wasnt overloaded.

i guess, this is something to remember and look out for.

[big tim]

A #12AWG copper wire has a resistance of 1.588ohm/1000ft. A 100ft. cord would have a resistance of 200/1000 x 1.588 = 0.3176ohm. if the cord is supplying a load of 10Amp the voltage across the full length of the cord would be 10 x 0.3176 = 3.176Volt. The wattage to be dissipated along the length of the cord is 10 x 3.176 = 31.76Watt. A little more then a 30 Watt bulb. I don't think you would have to worry about the reel getting warm enough to create a fire hazard.
You can always do a test, keep an eye on it and see what happens!

Tim

[Slik Geek]

The potential fire hazard isn't a result of the wire getting so hot that the insulation ignites. (It would take a tremendous amount of current for the wires to reach that temperature). The fire hazard comes as a result of the wire getting hot enough to exceed the temperature rating of the insulation. At excessive temperatures, the insulation breaks down. Overheated insulation often becomes brittle and flakes off, exposing the conductor.

Some cord insulation ratings may be as low as 60 degrees C. If your application demands current at levels near the maximum rating of the cord reel for extended periods of time in warm ambient temperatures, you may exceed the wire temperature rating deep inside the coil. The flexing of the insulation when the reel is extended and then recoiled could accelerate the insulation breakdown.

If your high current usage is intermittent (a few minutes in length rather than continuously for an hour), the wire probably isn't getting very hot. You can get a good idea by experimenting with the wire coiled up as much as possible (worst-case scenario). After your maximum normal usage time, immediately uncoil the cord completely and feel how hot the cord is at the entrance to the enclosure. If it is uncomfortable to hold in your hand, then you probably shouldn't use the cord for that high-current application when it is coiled up.

On the other hand, if you have a high current application, you might be better served to use a "normal" extension cord and avoid the extra voltage drop of the slip ring (or whatever other mechanism which is used to transfer the power to the rotation reel).

[Daryl]

By using a coiled or balled up cord you are creating a transformer. When under load the transformer has an impedence that causes that area of the cord to heat up. Somebody with a bit more electronics knowledge can expand on this.

[Slik Geek]

By using a coiled or balled up cord you are creating a transformer. When under load the transformer has an impedence that causes that area of the cord to heat up. Somebody with a bit more electronics knowledge can expand on this.

A coiled wire actually creates a "solenoid". A transformer consists of two conductor coils in close enough proximity and proper orientation to provide efficient coupling.

The inductance of the power cord in this wire coil example is insignificant for several reasons, including the fact that the operating frequency is very low (50 or 60 Hz). Impedance as a result of inductance is proportional to frequency. (Double the frequency = double the impedance).

Also, each turn of the solenoid coil consists of a two conductor cable with wires in close proximity, carrying current in opposite directions. The magnetic fields almost perfectly cancel each other, eliminating almost all of the inductance.

Perhaps most significant in all of this is that impedance caused by inductance does not result in energy dissipation, only energy storage. Thus, no heat would be dissipated as result of the inductance.

BTW: Under load, a transformer does dissipate heat. This is primarily due to the resistance of the wiring in the transformer. (There are other factors which generate heat, such as core loss).

[LCHIEN]

A coiled wire actually creates a "solenoid". A transformer consists of two conductor coils in close enough proximity and proper orientation to provide efficient coupling.

The inductance of the power cord in this wire coil example is insignificant for several reasons, including the fact that the operating frequency is very low (50 or 60 Hz). Impedance as a result of inductance is proportional to frequency. (Double the frequency = double the impedance).

Also, each turn of the solenoid coil consists of a two conductor cable with wires in close proximity, carrying current in opposite directions. The magnetic fields almost perfectly cancel each other, eliminating almost all of the inductance.

Perhaps most significant in all of this is that impedance caused by inductance does not result in energy dissipation, only energy storage. Thus, no heat would be dissipated as result of the inductance.

BTW: Under load, a transformer does dissipate heat. This is primarily due to the resistance of the wiring in the transformer. (There are other factors which generate heat, such as core loss).

Exactly. A case of no knowledge is dangerous, a little knowledge can be even more dangerous.

[crokett]

Solenoids? Transformers?

I will just pull the cord all the way out when I use it. Then there is nothing to worry about.