That's quite interesting, when I installed my brothers car stereo I had a lot of trouble trying to get the local branch of Halfords (UK car shop) to order me some decent large-gauge cable as they felt it was unneccessary. The system in question consisted of a pair of Kicker ZR1000 amps running at 2 ohms into four 15inch Kicker SoloBaric subs in the back of a Vauxhall Nova. The amps come with 120 amp fuse holders and recommend cable capable of handling at least 100 amps. We could only run the system with the engine on and idling at 2500 RPM, very nice!