What are the safety concerns in running low voltage wire to LEDs behind a wall?
Speaker wire works well for this, and you can get in-wall rated speaker wire, which usually has a 2nd common insulation around both insulated wires (like cat5). You can of course use regular mains-rated wiring in wall, but it's hard to tuck into tight spaces where you might want to hide an LED strip, and connecting to it legally takes a lot of space.
Buy stranded wire with flexible jacket materials like silicone to have an easier time &quot;origami&quot;-ing and hiding. You don't need oxygen free copper or anything fancy. Buy a bigger roll than you need; doubling the length is usually only 25-50% more up-front cost.
In terms of size for LED lighting, 20AWG is a good starting point for typical run lengths and a few watts. Subtract 1 gauge from 20 for every amp (12w/24w) to avoid voltage drop. So, if you need 6 amps, use 14AWG. This correlates decently to the recommended power transmission amp ratings. To be sure, that thickness is overkill in terms of fire safety but it provides voltage consistency to the strips, allowing you to very accurately match/correlate brightness levels by counting strip segments.