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RVelectricity – Just Ask Mike (J.A.M.): Do coiled extension cords heat up from inductive heating?

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. Today I discuss coiled extension cords.


 

Dear Mike,
Our all-electric coach has a 36-foot-long 50-amp cable wound up on a motorized cable reel. Is it necessary to completely unwind it before plugging it into a power outlet? I’ve heard that practice recommended to prevent overheating from electromagnetic induction, but wasn’t sure if, say, 20 feet of cable left on a reel would cause much electromagnetic induction heating. Piling an extra 20 feet of cable on the ground is a pain if not needed! Thanks for any insight. —Bruce

Dear Bruce,
Actually, electromagnetic induction heating of a wrapped up extension cord is an urban myth. First of all, any impedance caused by this inductor would be negligible at a 60 Hz frequency. And because there’s a matching neutral conductor that’s 180 degrees out of phase with the load current, any magnetic effects should be nulled out.


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Extension cord can overheat without adequate airflow around it

However, there can be an increase in the temperature due to lack of airflow if the cable is jammed into a very small space without air infiltration. This is especially evident when subjecting a SMALL gauge extension cord to a LARGE amount of current.

So, try it with the cable still partially on the reel, but check it for overheating by touching it with your hand. If it feels hot, then turn off power and unreel those last 20 feet.

Here is what I first wrote about this issue back in 2017, and the advice is still good.

Let’s play safe out there….

Send your questions to me at my new RVelectricity forum here.

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.

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Tommy Molnar
20 days ago

Interesting article. When we are boondocking I plug us into ourselves. To explain this, I’ve run a large extension cord from our front mounted 2000 watt inverter (in our TT) to the rear of our trailer where our power cord gets shoved into a space accessed by a small door (like most trailers used to do). I plug the shore power cord into this extension cord (which ends in an electrical box from local Home Depot) and this powers all the ac outlets in the trailer. Works great. However, I have on some occasions noticed the cord being warm to the touch. Normally the only ac stuff running is the Dish box. In the morning wifey uses her hair dryer. We never use the ‘nuker’ while the hair dryer is in use either. My question is, does the fact that the ac power cord is just jumbled up in that small storage space cause the heat buildup, and should I be concerned? Oh and we recently added an ac fridge to replace our dead RV fridge. We have 700 watts on the roof and they charge two Lithium batteries.

Leonard Rempel
20 days ago
Reply to  Tommy Molnar

We did the same for a while, however we hard wired in a transfer switch with a remote control for the inverter inside the trailer. Now just a push of a button “lights” up the whole electrical panel as if we were on shore power. Key is to use appropriately sized wire from the inverter to the transfer switch. The convenience is a game changer when without electrical hook-ups!

Larry Lee
19 days ago
Reply to  Tommy Molnar

Tommy M, I really like your idea, however, could you improve on it by pulling your 30 power cord all the way out and shortening the extension cord (and the total wiring from front inverter to back input).

Tommy Molnar
19 days ago
Reply to  Larry Lee

I thought about something like that initially (20+ years ago when I first came up with this). The whole idea was to not have to haul out the 30′ of shore cord. I’ve got a remote switch for the inverter inside, and the CONverter is plugged into a power strip so I can shut it off when the inverter is running. When we’re leaving the house on a total boondock trip I plug us in, stuff it all in that power cord box, and forget about it for the entire trip. And now that we have a 120v fridge (long story) the inverter will be getting more use.

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