In a car audio environment, the power wire should be oversized if anything, due to the fact that the wire is usually ran under carpet, seats, etc. Smaller wire WILL heat up under high current loads, thus being a safety concern. My current system is around 500 watts with 8 ga. wire. I would be more comfortable with 4 ga. but it is more of the family ride, and the system doesn't get loud very often, therefore, the actual current draw is low, 90% of the time. It's very rare that the thing get played at over 50%.