amp install question
 

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

Another thing that helps a lot is to keep the ohms load to 4ohms or more. The lower ohm loads draw more power and also create a lot more heat in the amp.

Jon

After reading your posts I will run 4ga power wire to the amps. Now for the ground wires: Will there be a problem if I run a 4ga from the battery and then go into 2 8ga wires that will go into the amps. I always heard that each amp needs its own separate ground wire back to the battery. My amps have capacity for 8ga power and ground wires. I'm trying to keep this as simple as possible.

Simple is good. However you do the power also do the ground. Keep it the same. Good luck! Craig

no you can put them both on the 4 ga block but also to avoid a ground loop condition your stereo must also ground to the same
point mutiple grounds will usually cause a ground loop which will pick up the ingnition and can be heard as background noise.

I would run 2 seperate power feeds and 2 seperate grounds- the voltage drops, etc. caused by one amp will also show up at the second amp with common leads.

Amp capacity of wire is determined not only by conductor size, but also the insulation temperature rating (rating is degrees C). Most wet location rated insulations have a 75 degree rating, and some have a 60 degree rating. The wet location types will generally have a 'W' in the wire type classsification, which should be stamped on the insulation. Some common wet use insulation types are TW, THW, THWN. I don't have marine types handy and don't want to go by memory. Heres an example from the National Electrical Code:

size# 75 deg, amps 90 deg, amps
THW,THWN THHN
10 35 40
8 50 55
6 65 75
4 85 95

For fire protection and compliance with National Electrical Code, the wire should be protected for the rated amperage, or the next higher amperage if no exact fuse is available. The overcurrent protection is ideally to be located at the source point, but with a battery setup this is not always possible.

On automobiles they use fusible links which are fuse wire- sometimes directly at the battery and sometines from a terminal point mounted near the battery.

The Coast Guard does require compliance with National Electrical Code- so it looks good to them if they ever start inspecting that closely, too.

Also, you should always provide overcurrent protection at each point at which conductor sizes change. An 85 amp fuse on a #4 main feed will not protect a #8 wire connected to it!

I would run the 2 #8 positive conductors from the battery to a fuse block mounted as close to the batteries as possible, Each #8 wire then feeds a fuse,such as a 50 amp for #8 75 degree rated wire. then feed the amps from that point. Or, get some fusible links, with spares.

The fuse or breaker you install can be rated somewhat higher than what is installed in the amp as long as it is sized to protect the wire. If the amp has a 30 amp fuse and you select a 40 or 50 amp main fuse, the fuse in the amp would normally blow first due to a lower amp rating. The fusible link or main fuse will blow only for a short or overload between the main fuse and amp.

I hope this helps!!!!
Bulldog aka Ronnie

I would oversize the wires up to #6 for each amp-- The lower voltage drop will help keep the amps cooler and the cost difference isn't much. You won't be sorry. I just bought a 75x4-200x1 sub amp that I plan on putting in my boat. I mounted the 1500 W inverter ( works the same as a sterio amp in a lot of ways ) under the back seat ( on the vertical part of the back seat that faces the cockpit) it stays nice and dry and is well ventilated and close to the batteries. I plan on mounting the sterio amp on the other side.