Originally Posted by BCK
I don’t pull mine out all the way either most of the time but you are better off to do so unless using reduced load. RV cords are good quality and relatively large but the warnings are still there for a reason.
Coiling reduces the ability to dissipate heat and as heat increases so does resistance further adding to increased heat which is why in some cases the insulation can be compromised. The electrical code deals with safe heat dissipation by reducing the allowable ampacity for cords when in close proximity for a distance of 600mm (23”) or more which occurs when coiled. The #10 STW cord with 2 current carrying conductors is rated for 30A max load. Electrical Code rules for cords reduce the max current to allow for safe heat dissipation as follows: 2-3 coils = 80% or 24A max load; 4-12 coils = 70% or 21A max load; 13-21 coils = 60% or 18A max load; 22+ coils = 50% or 15A max load.
So you can see that there are actual reasons not to coil an extension cord and especially longer ones with smaller cable size carrying close to their max load. The percentages for reducing max current apply to all rated cord ampacities.
The myth part is around induction. In a 2 wire AC cct no induction occurs because the voltage and current curves in the two conductors are exactly opposite at any given time and effectively cancels to zero. Induction, eddy currents, sheath currents etc. are a problem with single conductor AC cables and there are different precautions and install methods to correct for it.
What NEC article are you referencing? And neutral is not a "current carrying conductor" according to the NEC. It is the "grounded conductor" and the green wire is the "grounding conductor". There is only a single "current carrying conductor" in a 30A shore cord.
A lot of times folks look something up on Google regarding the NEC. However, they don't pay attention to the definitions of conductor types or what the that particular article is discussing. I've seen folks quote NEC articles regarding the wiring of hospital generator feeds like they apply to RVs. Or current derating for multiple conductors of a 3-phase system in metallic conduit like it applies to a RV shore cord. Just wondering what article of the NEC requires derating of coiled shore cords. I'm fairly familiar with the NEC but I might have missed something.
You'd think the folks who manufacture cord reels and get them tested by UL would understand the coiled cord derating requirement of the NEC.
And I think I'm done with flogging this deceased equine. If folks want to worry about a coiled shore cord setting their rig on fire that's fine with me. But it won't.