Use three wire Romex just in case you ever want to run a 220 volt amp.
You don’t need a 3 wire with ground Romex cable for 240V. A 2 wire with ground Romex is all that is needed.
Problem with using a 3 wire with ground Romex cable for a 2 wire circuit is what do you do with the unused conductor? Ground it? Leave it floating, taping both ends?
Floating the unused wire will act as an antenna and will introduce RF noise onto the circuit conductors.
If the unused wire is grounded because of the lay, position, of the conductor in the Romex cable, the hot and neutral current carrying conductor’s magnetic fields will induce a voltage on the grounded wire. Result is a ground loop and hum.
Worth mentioning again, as I have mentioned before in other posts, two conductor with ground NM sheathed cable (Romex) is not the best branch circuit wiring for controlling induced voltage from the magnetic fields of the hot and neutral current carrying conductors. The reason is because the paper filler that surrounds the bare ground wire does not rigidly hold the ground wire centered between the hot and neutral conductors. Twisting the Romex cable, imo, would make it even worse, not better.
A better Branch circuit wiring is 3 wire MC (Metal Clad) armored cable. (Hot, neutral, and green insulated ground) The 3 wires are tightly held together in a spiral twist housed inside a metallic armor. MC cable is manufactured with a steel armor or aluminum armor. Also manufactured with solid or stranded conductors. (Solid wire is recommended for audio branch circuit wiring.)
Example of MC armored cable.
http://www.afcweb.com/mc-metal-clad-cables/mc-lite-aluminum-armored-cable/
Best branch circuit wiring is to twist the hot and neutral conductors together and install the equipment ground along side the twisted pair in a conduit.
Jim
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