By Mike Sokol
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 I 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.
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 the 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….
Mike Sokol wrote this when he was a columnist for RVtravel.com. He has since moved on and is therefore unable to respond to comments.
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RVT1244
This again?
I would add, ANY extension cord that feels warm is overloaded.
Something to be careful of with cord reels is DO NOT move the reel when power is on. Usually these reels have “brushes” to transmit the power from the reel into the RV. Turning those contact brushes with power on can cause arcing and burning between them greatly reducing life of the cord reel.
Mike what I was taught when excess wire is out just do a figure 8. Let’s air flow and looks neater, than a pile.