(2) ground wiring questions.

[philwsailz]

the amps I am installing are a JL marine M400/4 amp and an Exile Harpoon.

Both suggest the use of 4 awg wire for power and ground.

I am planning on running the power wire from each amp to the distribution block via 4 AWG, thru the MANL fuse, and then thru a 2 AWG wire to the battery.

I will remove the jumper plate from the distribution block, thus creating an inline fuse holder for each power wire.

I'm doing this because I have plenty of 2 AWG wire laying around the house.

I will run the two 4 awg ground wires into (1) 1/0 awg ground

Your #2 wire on the B+ side will be your potential bottleneck. It does not have the same cross-section as a pair of #4AWG conductors, FYI

Phil
Kicker

[SC Ink]

One #4 going into one #2 (with a manl fuse inbetween)

twice.

[philwsailz]

One #4 going into one #2 (with a manl fuse inbetween)

twice.

Oh!!!!

Each amp home runs to the batteries....

Gotcha! my bad.

Phil
Kicker

[sandm]

Sorry sandm, this sounds confrontational, and I don't mean it to. I just want to clarify, and quoting you made most sense.


My post above assumes that each of SC Inc's two amps recommend or require 4 ga. To get an equivalent of two pulls of 4 ga. going all the way back to the battery, one needs 1/0 to ge tthe equivalent amount of copper in the power cable. This is just published fact.

What we don't know is the amplifier manufacturer recommendations, or the amp models. If in fact he has two amps that can run on 8 ga, the 2 ga primary wire will be fine, but we don't know that. In fact, if he has two amps that only recommend 8 ga, he can get away with using 4 ga as his primary wire, but again, we don't know that. I only wanted to create a clean wiring scheme that preserved the amount of cooper present in the two #4AWG cables between the amp and the distribution block, based on the facts provided.


Phil
Kicker

no worries phil. I agree with you, and was only pointing out that you don't need to automatically assume a 1/0. I would concur with the recommendation as you post it, but based on ed's response of having a ton of 2gauge lying around, I would wonder why you would not mimic the same run of ground wires as opposed to buying 1/0 other than the simplicity of running a single wire, except that you are already running 2 power wires.

[EarmarkMarine]

I look at assessing the cable size a little differently.
Start by determining the maximum and collective fusing for all amplifiers. Note, its unlikely that you will ever draw this much current. Even though you can exceed the fuse rating for a certain duration before it blows the amplifier total fuse amperage also represents an extreme operating condition to protect the amplifier.
Once you have the total max current draw plus the total distance of the main run for both positive and negative then you want a gauge of primary wire that has low enough resistance that you will not have an appreciable voltage drop.
Once you have the correct size of primary supply positive and ground you can drop down a size after the distribution blocks for the extensions to the two or three amplifiers. Since the distribution blocks are typically as close to the amplifiers as possible its usually the short extensions that are overkill for their actual usage.
You would have to have a ton of power or terribly inefficient amplifiers to compromise the amplifiers' performance using 2-gauge cable for a short primary run within the port locker. However, if there is considerable separation between the batteries and amplifiers this could change the requirements.
I would definitely trust 2-gauge to handle 150 to 200 amps of total potential draw over a couple of feet. And then step down to 4-gauge for the two or three very short individual extensions.
Remember that we may have an 8-foot positive and 8-foot negative for a total loop of 16 feet in many boats. A car may have a 17-foot positive run to the battery and a 2-foot negative run to the car body or frame. In many cars I would trust the longer 1 or 2-gauge ground cable before trusting the conductive properties of the car body.
So begin with the larger primary run based on your collective current draw. The smaller and shorter extensions at a step down in wire gauge are going to be plenty.

David
Earmark Marine