Does coiled extension cord heat up in storage bucket?

Does coiled extension cord heat up in storage bucket?

Hey Mike,
I was thinking about getting a bucket to store my shore power extension cord, or maybe even one of those fancy reels. But my neighbor who’s an electrician told me that the coil of wire will create some sort of induction heating effect and the wire will get hot. He recommends that I pull the entire extension cord out of the bucket and lay it all flat on the ground. Is that true? If so, what’s the theory behind this phenomenon? —Nick

Hi Nick,
Thanks for writing. Boy, this is a golden oldie that just won’t go away. Below are two pictures of what you’re talking about. A fancy cord reel can cost up to a few hundred bucks but looks very professional, while the cheap cord in a bucket only costs $5 and looks a little less professional but still gets the job done.

As a pro sound engineer I often have to contend with really large and long power cables, as big as 2/0 or 4/0 gauge, which can carry 200 to 400 amperes of current. And we were always told by management that it all had to be uncoiled out of its road case and laid on the ground or induction heating would melt the wires. So after a few gigs of unwrapping and rewrapping hundreds of pounds of 2/0 feeder cable I did some calculations and found that any induction from the coil of wire was so low as to be nearly unmeasurable, and any heating effects from induction would be below the level of my instrument noise and calibration. In short, if there were any heating effects going on, it wasn’t due to induction from the wire in a coil.

However, I did discover that an extension cord placed in a box without ventilation would indeed heat up a little, and it didn’t matter if the cord was coiled or loosely folded to reduce any induction eddy effects. So it really seemed like a lack of any air ventilation around the power cords was concentrating the normal heating due to regular voltage drops into a small space. But even that heating was negligible under reasonable power draw on the cable.

However, if you did use the cable up near its amperage limit while in a tightly closed box, it could heat up to the point of becoming a fire hazard. Again, this has nothing to do with induction heating from eddy currents. It’s due to a few hundred watts of heating from normal voltage drop over the length of an extension cord concentrated into a very small box without any air ventilation.

So what does this mean to you? Well, if you plan on having 90 feet of an undersized extension cord jammed into a small, unventilated space in your RV, then it can be a fire hazard. However, any exterior mount of an extension cord reel or bucket with a few air holes should be completely safe. To know for sure, just touch the extension cord periodically while using it under load. It might feel slightly warm to the touch and that’s OK.

However, if it feels like a toaster oven then you’re doing something terribly wrong and you need to shut it off and disconnect immediately. And never use too small of an extension cord for your shore power connection. You’ve seen many of my charts here already, so I won’t bore you with gauge sizes. But a 30-amp RV shore power cord MUST be at least 10-gauge size. Never overload an extension cord or you’ll be sorry.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

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6 thoughts on “Does coiled extension cord heat up in storage bucket?

  1. Tom Becher

    I always thought that you needed a steel or iron core to create an induction. I had a cord reel that heated up badly when we forgot to unwind the cord. It had a steel drum. Just having it in a plastic bucket should not create an induction coil but some heat would be made just because of voltage drop.

    1. Mike Sokol

      Actually, ANY coil of wire will create an inductor. But an iron core really increases the effect. Eddy currents can occur in this iron core, which is why transformers don’t use solid metal cores. They’re usually made from a stack of E and I shaped pieces that are varnished and electrically separated from each other. That’s specifically designed to eliminate eddy currents and the heat effect it produces.

  2. Catherine

    Would using one of those wire mesh-type garbage cans work better for airflow around the cord?

    1. Mike Sokol

      Yes, it would. Any air flow at all would prevent the heat buildup. And more airflow is better.

  3. Sandi

    Our 2nd year to camping with our 29’ RV (first year was visiting parks in FL for weekend visits and getting to know our RV), We left SE FL end of June for a 2-month adventure ending our northern trek at Copper Harbor, MI. We elected to not pull a vehicle on this maiden 2-month adventure and rely on a bicycle for an emergency situation. Due to increasing traffic our Interstate highway system, we decided to avoid Interstates. A trip to my local AAA office found that they were only able to prepare trip information on Interstates. Loaded with maps & a good atlas we did not regret 1 minute of our travels thru FL, GA, TN, KY, OH, & MI. And only time we had to jump on Interstates for short jaunts were from Venice FL to north of Tampa, and around Lexington, KY (where we elected to cross the Ohio River at Maysville avoiding crossing at Cincinnati which has always been a traffic nightmare even in a car. Made sure we always had a reservation for the upcoming nite (using Allstays & Good Sam apps on my iPad & then reviewing parks). Our favorite was a find on Lake Cumberland, Conley Bottom where we ended up staying for a week and met a wonderful couple from that area that we still keep in touch with. Our only problem was an accident in GA when a lady pulled out in front of us from a side street and did damage to driver side headlight, bumper, grill…..but duck tape held all together for another 4000 miles till we got home. Her car was not as lucky and had to be towed away. My thought: REALLY….are we not so big that you did not see us in that middle lane of 3 lanes?????

    1. Dr4Film ----- Richard

      Sandi, did you mean to post this comment under a different topic because after reading through your post there was nothing in it that had anything to do with the subject, “Does coiled extension cord heat up in storage bucket?”.

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