My old system was stolen 2 months ago and I am now mounting the amplifiers inside the cabin to hopefully deter the thieves. The old amps were wired only about 6 feet from the battery and used 8ga power and ground wire from the battery to the amplifiers. I now have about a 20 foot run from the battery to the amps and I don't know whether I should use one 4ga power wire and then go to a distribution block near the amps and then go to (2) 8 gauge or should I run (2) 8ga wires all the way from the battery to the amp? Can the ground wires also be 8ga going from each amp to the (-) battery terminal. The amps are Rockford Fosgate 500x (62.5x4) and the 400s (100wx2).

start with a marine rated fuse at the begining of the 4ga power wire and then go to a fused distribution block near the amps
and then go to (2) 8 gauge if under a few feet. All my amps use external fuses I just put in the right glass fuse
in my case two 60 amp fuses, check you manufactures recommemded fuse size for each amp

FIRST THING, PUT A FUSE or CIRCUIT BRAKER with a FOOT of the BATTERY! This is the most important thing you can do to avoid an electricle fire on you boat. A fuse by the amp only protects the amp's NOT THE BOAT! Otherwise if it shorts out some how that hole 4 or 8 gauge wire will still be hot. And that size power wire with a big battery can burn a glass boat to the water line. Heed this. Charlie

I've already got a 100A circuit breaker about 1 foot away from the battery. I should have put that in my initial post. It has a 4 ga wire going to the breaker and then there were (2) 8g coming off from there to the amps.

Go with the 4Ga up to the amps then a distribution block with 2 8 Ga. Make the 8Ga run as short as possible also to get the most current availible to the amps.

I would highly recommend the 4 ga for the longest run it will keep the amp and the wire from getting hot while you jamming at louder volumes also it is imperative that the ground be the same length as your positive lengths and sizes or the system sees the smallest gauge and you would waste all that 4ga and you should also use large ga speaker wire and keep all those lenghts running in pairs the same lengths aswell to maintain impediance. A stereo is only as good as its weakest link so keep them out and have a strong chain. Good Luck!. Craig (spent many years as an installer)

2 8 ga wires have the same power carrying capacity as one 4 ga wire. The two 8 ga wires, some will argue, would be better then a single 4 ga wire.

Jon

learn how to use this and you will understand
1000watt rated system will have a 1.44v drop on 40 feet of 4ga
wire 20 black 20 red total circuit length =40
600watt system would produce a .879v drop
I like my amps close to the battery. On boats a dry place is not always avaible though.

one 4 ga will hold higher current at higher voltage than two
8ga with what you are running either would work but one
4ga will be easier to run and look better, but weigh more.
the length does not need to be the same, but do use the same
ga for any circuit.

Damn apache77 you beat me to it. I was so tired last night I made a huge mistake. You are correct a 4 ga will carry more. Two 6 Ga wires are the same as a 4 ga.

The Rockford amps sometimes have dual 8 ga inputs. Check your amp and see. That would give you 3 wire runs required.

Jon