Is there a minimum length for power cords?

Another manufacturer says no less than 3 feet. And some cable companies say that less than 8 feet is not ideal for speaker cables.

I think the manufacturers just want to sell us more wire.

Who's cables are we talking about here? I don't think anyone mentioned any brands up to this point. I'm guessing that the OP is referring to Shunyata, but it would be helpful to know for sure because I'd like to see if other manufactures give the same reason for the cables sounding better at a minimum length.

The Shunyata website says to not use a power cord under three feet long. Mapleshade says 8 feet is ideal for speaker cables - not more, not less.

... any length shorter than 1.8 meters (5.9 feet)will begin to degrade the effectiveness of the shielding and filtering capabilities; regardless of who is the manufacturer.

But on the other hand the resistance and inductance of the cord will increase in proportion to its length. Both of those increases can have adverse sonic consequences if large enough.

Personally, however, assuming adequate gauge for the application and assuming cord designs that are identical aside from length I suspect that in most and perhaps just about all systems none of these factors are likely to be great enough to make an audible difference for lengths of up to 8 or 10 feet or so, and perhaps more.

And to prove otherwise would require, as I see it, performing comparisons between different lengths of identical cords that are repeated multiple times, going back and forth between the two lengths to assure that the results are consistent and that perceived differences are not the result of extraneous variables or misperception. I doubt that very many audiophiles have done that, and even if some have I see no reason to expect their results to be applicable to different components, system configurations, and AC characteristics.

Regards,
-- Al