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-   -   When is 0 guage wire actually required? (http://www.diyaudio.com/forums/car-audio/110227-0-guage-wire-actually-required.html)

 groover1234 17th October 2007 12:34 PM

When is 0 guage wire actually required?

Hi folks,

It seems to be the trend that if you can afford to buy wire as thick as concrete drain pipes then you should use it.

At what point do you need what guage wire? Is it based on how many watts RMS your amplifier is? how many fuses it has which is a rough guide to how many amperes it will draw?

There must be a logical flow as to when and why you need to use a particular guage wire and I'd really like to know.

Thanks
~groover

 error401 17th October 2007 01:19 PM

Re: When is 0 guage wire actually required?

Quote:
 Originally posted by groover1234 Hi folks, It seems to be the trend that if you can afford to buy wire as thick as concrete drain pipes then you should use it. At what point do you need what guage wire? Is it based on how many watts RMS your amplifier is? how many fuses it has which is a rough guide to how many amperes it will draw? There must be a logical flow as to when and why you need to use a particular guage wire and I'd really like to know. Thanks ~groover
At the end of the day, it's based on the current passing through the wire.

The limit comes from the ability of the wire to handle heat dissipation, and how much voltage drop over the wire you will tolerate. You just need to know the max RMS current draw of the devices and the diameter of the wire and you can calculate all of this.

Basically the cross sectional area and length of the wire determine its resistance. You can then use Ohm's law to determine voltage drop and the power dissipated in the wire, and if you wanted to determine how much the wire will heat up under load.

There are commonly accepted guidelines for the safe current carried by a given gauge wire. A quick Google turns up http://www.powerstream.com/Wire_Size.htm

 groover1234 17th October 2007 01:34 PM

Thank you. I suppose using that table I can base it on the fuses on the amplifier. If the amplifiers total fuse rating is 150A then, I need to use 0 guage wire.

I just bought one of these and I know that my current 8 guage just won't be enough. I was unsure as to whether I could get away with 2 guage as that is significantly cheaper than 0 guage.

OAX3200

 troystg 17th October 2007 01:41 PM

I seriously DOUBT you will listen at constant levels that will draw 150 AMPS.

The amplifier may be capable but usually it is not continuous.

Put a stiffening cap in the back and any "pulsing" or instantaneous current will be supplied by that. The cap will then "smooth" the current draw from the front and a smaller guage can be used.

VERY rarely does anyone other than competitors need more than 4 Ga.

A side note... A small set of caps at the head unit also makes a HUGE difference. Most new HU's are not passive and are "high powered" so caps there make a difference even if your not using the internal power.

 groover1234 17th October 2007 01:47 PM

Quote:
 Put a stiffening cap in the back and any "pulsing" or instantaneous current will be supplied by that. The cap will then "smooth" the current draw from the front and a smaller guage can be used.
Is that like a 1 farad capacitor? If so please look at my other thread

I am currently using an AudioControl parabass preamp and line level converter unit. Do I still need some capacitors before it hits the preamp? Are you referring to what is mentioned in this thread ?

 troystg 17th October 2007 02:29 PM

Replies posted.

 Flyin11 17th October 2007 03:10 PM

I hate to bust in on a thread but I didn't really see any reason to make a new one since everyone is on the same subject anyways...

So just as like a example...Judging from this cable chart from Crutchfield:

If the MTX amp I would be looking has 300watts X 1 RMS, I'd double that making 600 and then divide that by 13.8 which would give me 43.48 amperes. Then judging by the chart I would need just 10 gauge wire for 7-10 feet of wire which is the distance I have. I already have 8 gauge wire so I should be set. I just don't get it though as the specs on the amp from MTX recommend 4 gauge wire for the amp? Do the fuse amps come into effect? The amp I'm looking at has 2 20amp fuses for 40amps of power for the amp. I just got my security system straight so now I'm looking at maybe a bigger amp in the future. If I see my lights dimm or blink when using a bigger amp I guess I'll have to deal with it then. I have a 2003 Honda Civic EX Coupe and was told by a audio dealer near me that the Hondas have a really good alternator and electrical system and I should have no issues with my 180watt amp I have in there now and I don't...No blinking lights or anything which is really nice, except for a slight flicker when the fan in the engine turns on but I guess that's a usual thing.

 troystg 17th October 2007 03:27 PM

A stiffening cap would do more good than larger wire. 8Ga. is plenty for the short distance of a Civic.

Now don't get me wrong, BIG cable is good, but in most cases it is over kill. Companies and stores make money buy selling more, bigger, newer "stuff".

With <1k watts in a car or "regular" truck, a stiffening cap and 8 Ga. is plenty.

I run an Orion 2125sx and a/d/s/ P640.2 on 8 ga. with a 50 amp fuse and 1 Fd cap in the rear. Both amps connect at the cap. Never popped a fuse and it gets PLENTY of exercise on volume.

 zigzagflux 17th October 2007 04:25 PM

What troystg said.

Too much emphasis placed on large cable. Waste of money.

 Perry Babin 17th October 2007 05:20 PM

groover1234:

There are several factors you need to consider when choosing the wire. The most important are the loss of voltage at maximum current draw and the rise in temperature (of the wire) at the maximum current draw. For most car audio systems, a drop of 1/2v is generally used for the calculations.

The temperature rise at max current is determined (for the most part) by the resistance of the wire. The resistance is determined by the amount of copper. Since temperature rise is somewhat difficult to calculate (too many variables), you select a relatively conservative amount of copper for a given current draw. The amount of copper (cross section of the wire) is specified in circular mils (CM). A conservative/safe ratio of cm/amp of current is 300 cm/a. If you need 125 amps of current, you need 37,500 circular mills of copper. If you look up the number of cm for a given wire size on a chart, you'll find that 4g wire has ~42,000cm. 4g wire is safe for 125 amps of current.

To determine if the wire will drop more than 1/2v, you look up the resistance for the 4g wire. Using the resistance/foot and the length of the wire, you can calculate the total resistance. Then, using the max current draw and the total resistance you can use ohm's law to determine the total voltage drop.

All of this is covered in detail on the 'wire' page of my site.

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