ground cable length

[scotchnsoda 10+ year member]

I need to ground two amps. I plan on running an 8 ga from each amp's ground terminal to a distribution block, and from there, a 4 gauge to a back seat bolt. Unfortunately, this means at least 4 feet or so from each amp to the final grounding spot. Is that too long? I've heard people talk about having as short of a ground as possible, but I never heard why. Any help?

Forgot to mention, one amp is running 350 watts, the other is 100. The alternator puts out 80 amps.

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[SSS 18734 5,000+ posts]

You will be fine, especially if you're running 8 gauge power wire to your amps //content.invisioncic.com/y282845/emoticons/thumbsupwink.gif.129404938effda6ad9cca39e7f4b58a3.gif

 

[McIntosh 10+ year member]

I need to ground two amps. I plan on running an 8 ga from each amp's ground terminal to a distribution block, and from there, a 4 gauge to a back seat bolt. Unfortunately, this means at least 4 feet or so from each amp to the final grounding spot. Is that too long? I've heard people talk about having as short of a ground as possible, but I never heard why. Any help?
Forgot to mention, one amp is running 350 watts, the other is 100. The alternator puts out 80 amps.

I'd eliminate the distribution block (KISS) and ground them individually to separate bolts. Easier, cheaper and likely less resistance. Shorter is always better. Your alt's output is moot, I'm pretty sure your battery alone has a little more than that.

 

[smoka 10+ year member]

Like Mc said the shorter wire means less resistance, less resistance means slightly more power to your amp.

BUT in car audio, you often want to have all amps connected to the same point. This reduces the chance of ground loops.

I would keep the distro. The added resistance is not going to be noticable with amps you are running.

 

[ultimate157 5,000+ posts]

The idea for having the shortest run possible is because your car's chassis is a better conductor than most car audio setups' power wire.

That said, you're only running 400w and using 8 gauge wire which is more than sufficient for that setup... therefore you'll be fine. And keep them grounded to the same spot.

 

[scotchnsoda 10+ year member]

Thanks for the replies, everyone. I'm feeling much more confident about this setup now.

 

[McIntosh 10+ year member]

BUT in car audio, you often want to have all amps connected to the same point. This reduces the chance of ground loops.

I've never run into that problem (not that I've done hundreds of installs either) but I suppose its remotely possible.

 

[SocialStealth]

Whats a ground loop?

 

[smoka 10+ year member]

Whats a ground loop?

The shielding of your RCA's connect ground from your amp to your deck. If any extra current runs through the RCA's then you can get engine noise out of your speakers.

If you ground at two different spots, you have the same 12v going to the amps, but the grounds have a slightly different resistance (one spot may pass through more welds than another). This difference in resistance causes a slight potential energy difference between the two amps (i.e. if you connect a voltmeter between the 2 grounds spots you may see a small voltage). The RCA's on your cd player usually have the shielding connected together internally to ground. When this happens, the amp that sees the higher resistance might pass some ground current through the RCA's which interferes with the audio signal that is being sent. But when the amps are grounded in the same spot (or better yet connected straight to the neg batt terminal), there is not much chance for any potential energy to exist. Hope that makes sense, I could have probably explained it better.

If you watch this forum enough, engine whine is one of the most common topics. Some times its unavoidable even if you do everything right. Often people with Pioneer (or other) cd players will add a ground connection straight to the rca shield.

http://www.caraudio.com/forum/showthread.php?t=198477

I've never run into that problem (not that I've done hundreds of installs either) but I suppose its remotely possible.
You probably know how to make a proper ground. I would guess that a majority of people don't even scrape the paint off of their ground points, then they wonder why they are getting voltage drops or engine whine....

 

[McIntosh 10+ year member]

The shielding of your RCA's connect ground from your amp to your deck. If any extra current runs through the RCA's then you can get engine noise out of your speakers.
If you ground at two different spots, you have the same 12v going to the amps, but the grounds have a slightly different resistance (one spot may pass through more welds than another). This difference in resistance causes a slight potential energy difference between the two amps (i.e. if you connect a voltmeter between the 2 grounds spots you may see a small voltage). The RCA's on your cd player usually have the shielding connected together internally to ground. When this happens, the amp that sees the higher resistance might pass some ground current through the RCA's which interferes with the audio signal that is being sent. But when the amps are grounded in the same spot (or better yet connected straight to the neg batt terminal), there is not much chance for any potential energy to exist. Hope that makes sense, I could have probably explained it better.

If you watch this forum enough, engine whine is one of the most common topics. Some times its unavoidable even if you do everything right. Often people with Pioneer (or other) cd players will add a ground connection straight to the rca shield.

http://www.caraudio.com/forum/showthread.php?t=198477

AFAIK ground loops occur with weird combinations of components. You call it the RCA shield, I'll call it the ring (as opposed to the tip). It carries an audio signal and may or may not be grounded at either or both ends. Some combinations can certainly cause circulating curents (a ground loop). Millivolts make a difference when we're talking signal path. This is a hard row to hoe if you have problems. You may have to isolate your amp's chassis from ground altogether in extreme cases. I have run into this in industrial instrumentation. It can be a bear to chase down. Overall, your explanation was pretty good.