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Discussion Starter #1
Because I am NOT an electronics wizz, here is my question.

I am fitting a Pioneer Amp which is a nice 4x100W unit. I never really intend on cranking it up (unless Metallica's Master of Puppets is playing), I just want good sound, so to have it producing 400W of power at any given time should be a very rare occurance. -Especially when two of the speakers are a pair of little 6x4 JBL kick panel speakers.

I wish to run a 6 Gauge power feed from the junction block directly to the amp, but realized that this is un-fused.
Because my resto-mod is trying to stay relatively "period correct" and use OE parts whenever possible, I want to use the same type of 30Amp circuit breaker that is for power tops and/or power windows.

400W / 13.8V = 29amps.
Is this 30Amp circuit breaker a good idea?
Is the amp rating too high, too low or about right?
Is it better to use a fuse that needs replacing as opposed to one that will automatically reset?

 

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I do not recommend running the amp power wire from the junction block. The amp needs a clean, uninterupted, unmalested power source. The junction block distributes power to a number of OTHER power needs. EVERY stereo installation shop and EVERY competition stereo system runs the amp power directly from the battery. I know you want to stay "period correct", but if you want the system to sound good and do not want to run into any potential issues, then make the exception and run the power from the battery. Also, do not use circuit breakers. Again, all stereo shops do not use circuit breakers. By nature they are designed to reset and if you have a BAD ground issue, then you can run into some major problems. ONLY use fuses or a circuit breaker type system that is MANUALLY resetable. Unlike the fuse, when the circuit breaker type blows, it can be reset, but it has to be done manually, AFTER THE PROBLEM IS CORRECTED. If you have to have you car "correct", then you can hide a small stereo use battery somewhere and use it to run the amp exclusively. Please do it right. I have seen so many people do the wrong thing and run into problems later(poor sound, fire, etc) and have to spend more money to fix it right the second time and with a car of this nature, a fire can cause a major set back(both monetarilly and personally).
 

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Discussion Starter #4
Thanks for your advice Charlie, and the info on using a circuit breaker. :thumbsup:

Regarding the junction block, it is already connected directly to the positive terminal of the battery with a short ~12" 12-10GA wire -as per the OE wiring.

Because another battery is not going to be fitted in the car, and because I'm not going to add addtional terminals to the battery's OE style spring terminals, I figured the junction block would be the best location.
Connecting directly would only be by-passing ~12" 12-10GA of wire anyway, right?
 

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Connecting directly would only be by-passing ~12" 12-10GA of wire anyway, right?
Yes, but that 12" of wire is handling current from all the other circuits in the vehicle. Suppose that 12" of wire has 0.001 ohm of resistance and you're pulling 30A through that wire (disreagarding the amplifier current). That will generate a 0.03V signal on top of the 12V supply. Now amplify that 0.03V signal up to your 400Watt level and soon you'll hear why it's important to get a clean power source. Same scenario plays out for the ground as well which is why you'll see a ground wire ran directly from the battery to the amps.
 

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Reading what Steve described as "his needs" I still don't think a stock type breaker with 6 gauge wire would be a problem, and such a setup could easily be made to look as if it were born there.

Different peoples needs can be different. I designed my system for a thousand watts. My battery has both top and side terminal connectors, so I came right off the side terminal with a long generic battery cable for the stereo.
I mounted a 60 amp cartridge fuse under the washer bottel, and 4 gauge from there to the trunk. It's all wrapped in with the factory harness, and other than having 2 positive battery cables it's completely invisible.
 

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Don't get me wrong, I agree completely. I just wanted to point out how noise makes its way into the amps. It can be quite annoying and all the capacitor filters in the world won't do as much to remove it as a direct connection to the battery will. Even 12 short inches of wire can be problematic if it is also supplying current to the chassis electrical and carrying alternator charging current.

I like those breakers. Be sure to use two wrenches when tightening the terminals. I've spun a few by not holding the lower nut while tightening the top.
 

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Discussion Starter #8
Thanks Jim and Dave.

I think what I will do is see if I can modify my "Spring Ring" positive lead and swap in a 12" length of 6 gauge to the junction block.
6 gauge handles 55 amps, so there should be plenty left over for supplying the headlamps.

http://en.wikipedia.org/wiki/American_wire_gauge
 

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I agree with dnult. Amps are very susceptible to noise and I really don't think a resettable style circuit breaker is a safe protection device(for a stereo amp anyway). My system runs 0 gauge to a 200amp resettable circuit breaker, then 0 gauge to trunk where the distribution block is mounted. From there it runs 4 gauge to my mid/high's amp and 2 guage to my sub amp. By installing the amp power wire to the junction block, you are dividing that power to ALL the devices that get it's power from that block. Amps need CLEAN, UNMALESTED power. If you plan to ever play the stereo at an output other than being able to hear it in the car with the windows up, then you want the power source DIRECTLY from the battery. You can also damage an amp and your speakers by not giving them enough power. Distortion actually destroys speakers, not to mention sounds like S**T. If you are trying to restore the car to OEM then the amp would disqualify you anyway and if you are just trying to do a nice resto(not Concourse) then I don't think ANYONE would look down on you for having an amp installed the CORRECT way(not anyone in their right mind anyway). I would actually think people would look down on you for a "jerry rig" install before a "proper" install. Just my opinion. All you are going to see is a single 4 gauge power wire leading from the battery. If you run the wire right, then you can even hide it and all you'll see is the connection at the battery.

I am pleading with you on this. I have seen many car fires started by amps that have been installed incorrectly. You are smart to put in the circuit breaker, but I don't feel that an automatically resettable style breaker is proper in this application. Here are some examples of manually resettable style circuit breakers. Here is 100amp manually resettable circuit breaker.
http://www.rockfordfosgate.com/products/product_details.asp?cat_id=5&series_id=44&family_id=93&item_id=108314&locale=en_US&p_status=

Here is what you use in the trunk to run two amps from one power supply. The 4 gauge goes in and then you have two 8 gauge outputs.
http://www.rockfordfosgate.com/products/product_details.asp?cat_id=5&series_id=39&family_id=72&item_id=108332&locale=en_US&p_status=

For some reason the links take a few seconds. The website may be having some issues. Don't "X" it off, it will come up. The reason I am trying to convince you of using the proper installation methods on this is because I learned the hardway. It doesn't take much power to start a fire. You would think that your amp is only 400W, but it can still build up heat. Even with a resettable circuit breaker. That is why you will NEVER FIND THEM IN ANY TYPE OF COMPETITION stereo or EVER USED BY ANY REPUTABLE stereo installation shop. Don't learn the hard way like I did.
 

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Discussion Starter #10 (Edited)
Thanks Charlie. ;)

I have decided to run a 6 GA directly from the battery terminals. I am using OE style Spring Rings and have been able to do this discretely.

As far as the circuit breaker goes, the 100amp is way more than I need. The only reason I am installing a breaker is to protect the positive cable in case some happens to it between the battery and the amplifier. The amplifier has it's own 20amp fuses to protect itself anyway..
I guess what I really need is a 30amp manually resettable circuit breaker, so the power doesn't keep coming back on on it's own.

Thanks for your advice.
 

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A 100 Amp breaker may be asking for trouble. Wire sizing depends on the allowable temperature rise above ambient. I have a chart here from Belden that shows continuous current vs. temperature rise for wire gauges up to 8. If I extrapolate where 6 gauge wire would fall, it could handle 50 amps continuously at a 35*C temperature rise. Theoretically you could encounter a short circuit that resulted in a wire melt-down but still fell short of 100A. Food for thought.
 
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