People sometimes think of speaker wires as being low-voltage and they are not. Using 25 V-rated, or even 100 V, low-voltage lighting wire, is a not a good idea with speakers. I was trying to throw in a reminder that, while current flow is the primary cause of heating as Bill said, ignoring voltage ratings is inadvisable.
I agree it is essentially current that heats the wire, however you want to measure it (peak, average, RMS, whatever -- I assume you meant to say "RMS current").
I understand the relationship among dB, power, voltage, SPL, phons, Fletcher-Munson and all that jazz.
And I was in the sound biz long enough doing live sound to see plenty of wires go up in smoke... Mic cables for speakers, baling wire, transformer outputs twisted together to "double the power" (transformers REALLY stink when they are turned into slag!), etc. At least once a year some geetar player had to wire his biggest speaker directly to an extension cord and plug it in to the wall outlet to prove it could take it and play louder than the next guy's. Most could not.
Most people use larger wire guage these days, but in the 70's and 80's it was not uncommon for cheapo systems to come with 24 - 20 gauge wire, and then kids to use that same wire to hook their speakers up to a high(er)-powered amp and stress the wire to failure. Some would upgrade amp and speakers but not get new wire, same result. Especially when they hauled those speakers out on the deck to use for the block party. I dare say the power was a little more in that case than your average living or media room, not to mention that the RMS value of a clipped wave is much higher than that of a pure sine wave.
Whatever - Don
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley