seeing stars heh
Home and Business, aka Industrial, Commercial and Residential 120/240v AC electrical systems are notably different than the automotive 12-volt DC electrical systems. The MECP, which is a subsidiary of the CEMA (Consumer Electronics Manufacturers Association) and its principles outlined in its study guide are basic principles of Ohm's Law, Kirchoff's Voltage and Current Laws and the components used in DC circuitry.
It's incorrect to design your power wire size according to your amplifier's fuse size. Scientifically conducted lab tests have shown that PWM (Pulse Width Modulated) switching-type amplifiers, used for music reproduction, rarely draw a fraction of their maximum current.
The power wire charts you'll see (AWG, IASCA, etc...) assume that an amplifier draws maximum current contiuously--as does, say, a power drill, hair dryer, space heater, heat gun, vacuum cleaner....etc.--which is FAR, FAR from the case, so they are woefully inaccurate.
Here's something to consider: if an amplifier is driven to full power (i.e., head unit at full volume, with a properly set gain structure), it's still drawing only a fraction of the max possible current. The reason for this lies in the nature of the software. Most modern rock music has a "crest factor" of approximately 10dB. This means that even with the volume set to MAX, the average program material (not the peaks) causes your amplifier to produce only one tenth of it's max output; only on those infrequent peaks will the amplifier produce its maximum power...and those peaks are present in less than 5% of the music.
So, you can see that obsessing about power wire size is a waste of time, unless you're worried about impressing friends, or if you're going to compete in sanctioned sound-off shows, where you'll need to adhere to their wire size guidelines.
- So basically two things : an amp is not 100% efficient, more like 50%
A music signal is dynamic, most of the time the signal is only 10% of its peaks.
An Example:
Given all your amps are RMS values :
4x30 (front stage) + 2x75 (mid bass) + 1x400 (subs) = 670Wrms
50% efficient : 670 x 2 = 1340W
Music is dynamic : 10% of 1340W = 134W.
Your AVERAGE predicted draw while playing LOUD will be below 250W (<20A), so it shouldn't be that much of a problem. If you are going to compete in SPL, or are going to play pure 0dB sinewaves full blast, things will change dramatically though.
Additionally, for the fuse at the battery on your amp feed wire...you do not determine its value by adding the fuse ratings incorporated into whatever amp you have is using. If that were the case, try adding all the fuses up in a new Caddi ... where did they put the real
BIG fuse for all that?
You determine the feed wire fuse size must exceed total current/amperage draw, but be able to handle the total current/amperage.
According to the AWG wire guage current carrying capacity chart, at a length of 13-14ft 4ga will carry 125 amps, I agree ... however, in car audio, voltage drop is what is of concern. You want to supply your equipment with as much power as possible (14.1vdc would be nice
). Large gauge wires with respectively higher strand counts provides for a less resistive path and equates to a lower voltage drop across a given distance. Using Ohm's Law, in order to create 125 amps, at 13.6vdc (typical reading at the battery while) you would have to come up with 1700 watts of power (I=P/E).
One of the reasons IASCA's chart specs 0ga for carrying 125-150amps across a 13-16ft run is safety and as stated in their chart's notes, will provide the equipment with no less than a 0.5 volt drop. The AWG chart doesn't take into account for voltage drop, which is quite critical to the optimum operation of car audio equipment.
So you take the "charts" however you wish, but when you want to crunch numbers and the facts of how car audio systems perform, you use Ohm's Law to get realistic answers to what size wire...what size fuses at the battery and at the amp is not provided by the manufacturer, how much permissable voltage drop there can be in accordance with the manufacturers specifed power operating range for that amp/head unit.
As for where Kicker got their recommendation for using a 60amp fuse at the battery for the feed wire, I'm honestly not 100% sure where they derive it from, but I can contact either David Navone or Garry Biggs and ask. However, my amp has two blade 30amp fuses for protecting the amp from shorts from speaker wires, blown speakers or internal shorts. The fuse at the battery does, as you said protect the wire from possible fire and will blow if the wire or attached device shorts to chassis or battery ground. So you could short your speaker wires and blow your amp, but not blow the battery fuse...it would just be a incomplete circuit.
At any rate, its 6am and I'm tired...spent a few hours watching the meteor showers out at the beach...was nice and relaxing
time for bed.
