Cord Reels

[rmonroe]

Good morning, at lease its morning here in Cincinnati, Ohio.

Recently a discussion came up in regards to cord reels, both 120VAC and 480VAC. Is there a code that guides the use of cord reels?

Do to the inductance of the cord coiled up inside the reel housing during the current draw should the cord be completely pull out from the reel housing when in use?

Thanks

rmonroe

 

[kwired]

Lets just say that a single conductor wound on reel with magnetic properties will have much more induction effects than a multiconductor cord that contains all the conductors of same circuit. That cord will have a net magnetic field of zero if all conductors of the circuit are present, as they will cancel each other out.

Wind the single conductor on a non magnetic reel and there may still be some induction but not like there is with a magnetic core material.

Does that help you?

 

[fmtjfw]

Extension cord reels typically are labeled to require them to be fully unwound before use. The problem is not inductance, rather overheating.

I vaguely recall someone doing the following experiment:

1) take a 250 ft. roll of 12-2 NM
2) pass 20A through the roll
3) watch it meltdown and catch fire

 

[kwired]

Extension cord reels typically are labeled to require them to be fully unwound before use. The problem is not inductance, rather overheating.

I vaguely recall someone doing the following experiment:

1) take a 250 ft. roll of 12-2 NM
2) pass 20A through the roll
3) watch it meltdown and catch fire

I don't doubt that reel of 12-2 will produce some heat. I find it hard to believe it will melt down with 20 amps of load, and if it does will take some time to get to that point.

 

[fmtjfw]

Look at the bundling study

Look at the bundling study

see http://www.copper.org/applications/electrical/building/pdf/bundle_evaluation_report.pdf figure 4.

They have 6 cables bundled at 80% load (two each: 14-2, 12-2, and 10-2). In 5 hours the bundle is at 233 F, over the max of 194.

So if we bundle say 60 12-2 (a roll cross section of 10 x 6 cables) with 10 + 10 + 4 + 4 half exposed and the rest completely surrounded, I can believe the center of the cross-section will get really hot pretty soon.

You will note that I made my original statement in the form of an urban legend to give me some wiggle room. But after finding the study results I don't think I need the wiggle room.

 

[templdl]

I don't doubt that reel of 12-2 will produce some heat. I find it hard to believe it will melt down with 20 amps of load, and if it does will take some time to get to that point.

My son when he was a teenager melted one of mine down, welted it together. The rating for SJ cord and similar is in pen air. When you coil it up the heat can no longer dissipate and just keeps building up. As such reels should be completely extended when in use. I realize that there are those what me may judge a small lighting load that basically are a none issue and it is somewhat inconvenient to unwind the whole reel every time that we want to use if. Cord reels that have a dedicated light attached to the end my be linited to a 60w light bulb capacity. I repelace it with a 100w equivalent CFL which is awesome, cooler with less watts than a 60w incandecent.
But that fact remain that anything that is of a significant load will cause heating within a reel of wire building up to a point where it can be hazardous.

 

[don_resqcapt19]

The instructions for many cord reels specify that the cord be unwound before using. When I was in a rescue squad, we had 250' #12 cord reels and we would power 1000' watts of lights. Often we would not need the full 250', but when we did, we found that we could not completely unroll the cords. The inner layers had melted together. After we replaced the cords the policy was to put all 250' of cord on the ground when we were using them.