I have done a great deal of electrical work in my career and I’m with majorvices. Extension cords are intended for temporary use. If you need electrical power in a particular location, install a receptacle.
Functionally what is the difference between a freezer plugged into an extension cable and a freezer with a long cord? I get that many extension cords are insufficient gauge to act as a permanent cord for a freezer but if a sufficient gauge were used then what's the risk?
Basically it comes down to the wire gauge, heat dissipation and the wire protection. EMT conduit (metal tubing) is typically used when exposed in basements. If not EMT conduit, then the lesser quality product would be Romax. Also, extension cords do not have the ability to dissipate heat the way wire does in EMT, or Romax.
Also, the connections need to be considered. The connection (plug) is the “weak link” in the circuit. Using an extension cord would have a minimum of two weak links, instead of one.
If extension cords were the same as EMT or Romax, we could wire an entire house with extension cords.
Will extension cords work? Absolutely they will. I was merely offering advise from years of experience in electrical wiring and HVAC controls. Extension cords are intended for temporary, or light duty, use. Not for a major appliance in a basement.
You are partially accurate, EMT is used to protect the conductors, however it also has to be sized correctly based on the installed conductors to give you the heat dissipation. Romex should never, ever, ever be installed exposed - or in conduit as it is not rated for such uses. Romex is only designed for interior wall installations, again proper sizing based on the required load will account for the heat dissipation.
Another point to consider is the length of the cord, conductor size is not the only consideration here. A #14 wire is only good for its rating (15 amps) to a length of about 45 feet, longer than that will create too much resistance, lower the supplied voltage and increase the amperage respectively - this is where the heat comes from.
Basic extension cords marketed to home owners are not even 14 gauge wire, most are 16 - never use these, as these are cheaply made and in my opinion should not even be available to purchase.
My best suggestion is if you don't hire an electrician (best choice), and must use an extension cord (definitely not the best choice but will work), buy a "Heavy Duty" 12 gauge extension cord (these are expensive) keep the ends off the floor if there is any chance of flooding, and plug it into a GFCI protected outlet. Keep in mind to keep the length as short as possible.
I am a licensed master electrician with 29 years of experience.