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.
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
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.
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