Is there a minimum length for power cords?

5FT is best.

I personally like really long power cords. Most of mine are FOUR METERS long.
I have my stuff arranged to take advantage of long power cords. So the cords are not just piled up behind the rack.
My Furman REF20i conditioner os off tothe side and sso the four meter cords just reachthe top of thhe rack near me. Then the other way the cords just reach the amp between the speakers..

I make no claim that longer cords are better or not.
But for myself, the shortest cord I own is two meters.

I like short ones. The 3 in my 2-channel system are between 20-24" each. You don't have to worry about them getting in the way ..... and they're cheaper :^ )

"However, any length shorter than 1.8 meters (5.9 feet)will begin to degrade the effectiveness of the shielding and filtering capabilities"

Sounds plausible to the layman I guess. If it's true it would then depend on how badly your set-up needed the shielding and filtering to begin with. This has been discussed in a similar thread here recently
http://forum.audiogon.com/cgi-bin/fr.pl?fcabl&1396218203&&&/Power-cord-length-