what size power wire

[dropkick13 0]

I have a JBL BP1200.1 powering a rl P-12. From battery to amp is about 9 ft and ground is about 4 ft. The amp's plug looks like its for a 4ga. Should single 4ga runs be sufficient?

if so, who wants to buy some 1/0 and sell me 9 ft of 4ga??? (from the old setup)

[johnecon2001 82]

Just use the 1/0awg. Not going to hurt anything to run a larger wire.

ALSO, shorten your ground. That thing is waaaay to long.

[dropkick13 0]

Just use the 1/0awg. Not going to hurt anything to run a larger wire.

ALSO, shorten your ground. That thing is waaaay to long.

If I shorten my ground, I'll have to ground it to my body. I would have thought grounding to the frame would be much better.

[johnecon2001 82]

Not really, body resistance is quite low in comparison.

[djjdnap 78]

that amp is a beast, lol, although, its a clipping beast as well, i fudged up 2 subs wt it, lol...

But yea 4guage will work, but u cant go wrong wt bigger.

[helotaxi 46]

Not really, body resistance is quite low in comparison.

Body resistance low in comparison to a foot or two of 4 ga or 1/0 copper wire? Are you daft? 2.4 ten-thousandths of an ohm per foot for 4ga. Compared to a car body with an unknown path to ground and unknown electrical continuity to ground as well as one made from a material with 10x the resistance of copper, I'll take the extra foot or two of copper to get to the frame.

[rastaman 0]

Since when has a 4 foot ground become worse then a 3 foot ground? I currently have a 6 foot ground and a 4 foot ground so I can ground my amps to the same place(frame). No noise and no problems at all. If I wanted to go shorter, I'd have to ground separate and risk noise.

Short ground is a myth started by wire companies so they can sell you less wire for more money.

[johnecon2001 82]

Not really, body resistance is quite low in comparison.

Body resistance low in comparison to a foot or two of 4 ga or 1/0 copper wire? Are you daft? 2.4 ten-thousandths of an ohm per foot for 4ga. Compared to a car body with an unknown path to ground and unknown electrical continuity to ground as well as one made from a material with 10x the resistance of copper, I'll take the extra foot or two of copper to get to the frame.

Go measure resistance on a unibody car. It's as low as most wire.

I was an nonbeliever once too.

[///M5 2,833]

Even still if the wire supports the current a longer ground isn't really an issue anyways. The distance it "runs" through the uni-body isn't exactly short either...

[dropkick13 0]

For mental image's sake, I have an extended cab Silverado w/ the amp mounted on the back wall. So, how about if I attach the ground wire to a bolt going through the body, and then have another run of wire underneath my truck from that bolt to my frame?

On the Silverado forums, people say grounding to the body is a big no no. Perhaps this is vehicle specific (such as our trucks having a history of bad welds or something).

I'm still thinking running the 1/0 through a grommet straight to the frame would be best though. 4' does not seem like it would be a problem, especially since my power is 9-11'.

[helotaxi 46]

Has nothing to do with welds. The body is rubber mounted to the frame. There are a few small braided ground straps that connect the body to the frame. Grounding through a bolt to another wire that goes to the frame will work fine. Make sure you have a good connection above and below on the bolt.

John, if you can measure the resistance it's too high.

[ANeonRider 3]

Either way, in the end the current is going to go to the battery negative anyways, so whichever method you are more comfortable with will work.

[sqguy 0]

Come on you guys, steel conducts just fine and when you have a couple thousand pounds of it....it can conduct a lot of power, way more than your wire. But that is for unibody cars that are all welded together really, a truck is constructed differently. The cab and box sit on the frame and the fenders are bolted to the cab and front saddle. The saddle, cab, box all sit on rubber isolators, the ones you replace with taller units to bodylift a truck. The battery should have a ground to the fender that is bolted to the cab, a little stock one. But it is different than a car and the frame is IMO a good way to go. Only issue is your connection is out in the weather, I might seal it with something living in snow/rain/high humidity here.

[helotaxi 46]

Come on you guys, steel conducts just fine and when you have a couple thousand pounds of it....it can conduct a lot of power, way more than your wire.

Yes, a lot of steel would theoretically conduct a lot of current but the majority of the steel in the car does not lie in the conducting path between the usual ground and the battery ground strap. All that steel does you no good. Electrical current doesn't flow through the entire mass of steel of the car. That isn't the path of least resistance. The chassis in effect acts like a very large number of small conductors of differing resistance wired in parallel. The current flows along all these pathways in inverse proportion to the resistance of each pathway. If there is a pathway with very low resistance, it will carry the bulk of the current. It's this multi-path concept that most people fail to account for when considering how good a conductor a unibody car or the body of a truck really are. Each vehicle is different, not just make and model, but individual vehicles. Quality of welds, uniformity of the steel's alloy, stress risers in the steel from forming, lap joints, etc... It all makes for a giant "?" when asking how good of a conductor is a unibody. On the flip side, I can tell you almost exactly how good a conductor a piece of copper wire of a given gauge is.

Next what are you considering when you talk about "can conduct?" Capacity before thermal failure? Who cares. Sure the massive hunk of steel can shed more heat than a tight bundle of wire, but it will also generate more since it presents 10x the resistance per unit cross sectional area. It's that 10x resistance that is the limiting factor. Who cares if the the chassis can conduct a retarded amount of current before it melts, it's the voltage drop due to resistance that is important.

The frame on a truck is different because it is a large continuous piece of high cross sectional steel that runs the whole length of the vehicle and can take you right to the battery if you make sure to upgrade the chassis ground strap in front. Single path of high cross sectional area, pretty much ideal.

[///M5 2,833]

One other thing to note, quiet steel has a constrained dampening layer sandwiched between two layers of metal thus insulating it both acoustically and electrically. The cure of course is a clean connection on both sides, but I'd still prefer the frame in particular in a truck.

[ANeonRider 3]

Ya, if you have a frame, use it.

Drill a hole in the frame, tap the hole, and there you go, an excellent ground. Be sure to use dielectric grease on the connection.

[sqguy 0]

If a steel unibody is such a poor conductor then why does everyone use it, better run more copper cable back to the battery right?

Do you know how many welds it takes to hold together a 3,000 unibody car for the use it might see in its life? I have drilled many of them out, they are good welds or the lawyers would be even richer today. There are enough welds to not fail until the panel has been completely deformed.

[helotaxi 46]

If a steel unibody is such a poor conductor then why does everyone use it, better run more copper cable back to the battery right?

Do you know how many welds it takes to hold together a 3,000 unibody car for the use it might see in its life? I have drilled many of them out, they are good welds or the lawyers would be even richer today. There are enough welds to not fail until the panel has been completely deformed.

Have you measured the electrical resistance of those welds? The heat of the welding process changes the electrical properties of the steel and not for the better. The number of welds used are overkill so that a bunch can be of less than ideal quality and still hold the panels together. Lawyers win over engineers when it comes to design every time. Even if they were all perfect, they still aren't all in the current conducting path. The resistance is still and unknown quantity. A lot of people use the chassis as a ground because it is good enough for their purposes, that is far from qualifying it as the ideal ground for every situation. Low power, sure, it's fine and it's simple. Low current means low voltage drop regardless of resistance. Start getting into higher power situations and the ground becomes hugely important to getting good performance from the amps.

[dropkick13 0]

Ya, if you have a frame, use it.

Drill a hole in the frame, tap the hole, and there you go, an excellent ground. Be sure to use dielectric grease on the connection.

3/8" hole already there for me and I have already bought the grease and undercoat. Good to go...... I just remembered I need a rubber grommet....son of a.....

[sqguy 0]

The number of welds used are overkill so that a bunch can be of less than ideal quality and still hold the panels together. Lawyers win over engineers when it comes to design every time. Even if they were all perfect, they still aren't all in the current conducting path. The resistance is still and unknown quantity. A lot of people use the chassis as a ground because it is good enough for their purposes, that is far from qualifying it as the ideal ground for every situation. Low power, sure, it's fine and it's simple. Low current means low voltage drop regardless of resistance. Start getting into higher power situations and the ground becomes hugely important to getting good performance from the amps.

Right, because there are so many easy paths for the current to take. There is only one path with a wire. In the end you may be right, but you would have to make enough power under the hood to justify it, so what maybe 3 alternators or something? Big power is going to be in batteries next to the amps. Even three of the 1200w amps this guy has is not going to be hardly measurable in ground resistance with the proper connections to the body. The difference in steel and copper is -8th power or -7th power ohms per meter. I can't agree with you, but hey I might be wrong too and there could be some wacky steel car out there that makes it possible.

[buickid 0]

So what would everyone suggest grounding to in a unibody vehicle?

[helotaxi 46]

So what would everyone suggest grounding to in a unibody vehicle?

Whatever works. You can search for a good ground point somewhere on the body, or just go right to the battery.