I was in San Francisco last summer. Many of the houses up there are old and have very old wiring systems. There was a house burnt to the ground. The firemen there pointed to the source of the fire - what was left of the grow space. They said it appeared to be due to them using long extensions cords that were too small of a cord to keep the source from getting so hot it caught fire.

I've had 2 400 watt hps lamps in use since last August on 24/0. I was a bit nervous for a while about it even with 12 guage cords as it's running on a 15 amp breaker.