# What if u use too small guage a power cable?



## blamus (Mar 9, 2009)

Sounds obvious, but when you think about it in detail, what actually happens?

lets say I use 4G wire for an amp that says it recommends 1/0G, The only difference is that the 4G will have a higher resistance. That would mean the wire might get hot? but is that likely?

What are the actual problems of using wires that are too small?

obviously i am thinking this not because i am going to use too small a wire for my amp, its just that I ordered a 1kW amp but planning to use it at 4ohms, and its a pain to do the wiring again and I was wondering what would happen is I got lazy


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## Pseudonym (Apr 17, 2006)

Pretty sure the founder of this site uses something like 8 or 10ga wire for power/ground. Mayhaps 12.


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## emperorjj1 (Sep 10, 2008)

depends on how far from the battery it is, and how much current your drawing. consequences are there obvious melting wire fire ect but depends on the 4g and depends on the amp. If is decently efficient at 4 ohms you might be ok. the last thing that many people overlook is the effect on the amp and sub. lower voltage can lead to amp distortion or failure depending on how bad it is.

but if it makes you feel batter i've seen amps as big at 1500w rms at 1 ohm ran off 4g without any known issues.


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## Diru (May 23, 2006)

Under sized power wires get hot.

The voltage drops.

The hotter the wire the higher the resistance.

The higher the wire resistance, the more the voltage drop.

Now add the effects of this to the amplifier.

The more the voltage drops the more current it may need to keep the rails voltage up.

The hotter the amplifier power supply becomes and more inefficient. 

Enough voltage drop and things like under volt shut down will happen.

Other neat things like sagging rails can cause hard clipping <maybe I should say flat topping> in the output stage tricking it into speaker protect, thinking it is reading a DC offset.

So in a nut shell, use proper gauge wire for the current needs of the amplifiers.

One other thing, if you feel the need to run under the needed gauge, check your insurance policy. Just encase you burn your ride to the ground. A lot of companies won't cover stupidity.


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## freemind (Sep 11, 2008)

God kills a kitten!


If the manufacturer says to use a bigger run,

I'd use a bigger run.

Make sure that your grounds are the same guage as well.


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## emperorjj1 (Sep 10, 2008)

mind you while everyone is crying about needing what the manufacture recommends for wire size. too often what the wire says on the jacket has nothing to do with what the copper or worse cca inside actually is


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## JayinMI (Oct 18, 2008)

emperorjj1 said:


> mind you while everyone is crying about needing what the manufacture recommends for wire size. too often what the wire says on the jacket has nothing to do with what the copper or worse cca inside actually is


True. The cheap Scosche kits from Wal-Mart say 4 ga, but the actual wire is smaller than the JL Audio 8ga kits.

I had a suburban in the other day who had his install done by "his boy." They ran 4ga back to a big 4 channel and a PowerBass 1000WRMS sub amp running 1ohm. They ran 4 ga to distro blocks and then 8ga to the amps (and it was CHEAP 4 and 8 ga at that).

He complained his subs were cutting out. When I went to check the speaker terminal with my meter, my hand brushed the 8ga power wire and it was HOT! the casing had melted some too!

Don't be a cheap ass, buy the right wire...I usually run larger than required wire just so I don't a) have to worry about it, and b) I can upgrade later without gutting all my wire.

Jay


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## The Drake (Apr 3, 2007)

Are you serious? Why in the world are we spoon-feeding people? 

Do some research, its really not that hard. Here is a site for starters:

Basic Car Audio Electronics


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## Oliver (Jun 25, 2007)

if your amp was really expensive . . . I'd be concerned 

If it is cheap , then let it burn


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## jets88 (May 12, 2008)

I'd just like to say that you better make sure you have a proper fuse on that power wire. 125A max for 4 guage, as close as possible to the + battery terminal. I'm not sure how much current your pulling through it but if it gets too hot the jacket will melt, especially if its cheap wire. Definately checkout the link in post 8 it should answer all your ?'s


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## blamus (Mar 9, 2009)

Well, this was my chain of thoughts when I decided to ask a seemingly obvious question:

Consider these 2 amps, 

Clarion DPX1851 Mono subwoofer car amplifier &#151; 850 watts x 1 at 2 ohms at Crutchfield.com
[email protected], [email protected], 4ga

Clarion DPX11551 Mono subwoofer amplifier &#151; 1550 watts x 1 at 2 ohms at Crutchfield.com
[email protected], [email protected], 1/0ga

Notice that the 4ga amp puts out the same power at 2ohms as the 1/0ga amp puts out at 4ohms.

1. So, first question: is it correct to assume that the current draw for the 2ohm on 4ga amp will be double that of the 4ohm on 1/0ga amp when the power is constant?

2. If so, then next question: If the 4ga amp only needs 4ga wire running [email protected], surely for the 1/0ga amp running [email protected], using 4ga wire will be more than enough?

3. As I mentioned, for my install I will be running the amp at 4ohms. So the max power I can get is 850W anyway, so that means 4ga wire is all i need?

4. Now consider just one amp, the 1/0ga amp. Will running the amp at [email protected] have less THD than running [email protected]? In addition to being much more efficient.

If all the above are true, then if for my install I am only needing 850W of RMS clean power, by running the 1/0ga amp @ 4ohms, I get cleaner power and can use 4ga wire, and only a 100amp fuse? (the fuse required by the 4ga amp)

I was not asking to be spoon fed, I know it sounded like a stupid question, but when I thought about it in detail, it wasn't as clear cut.

Note that I am NOT trying to be cheap and not buy a 1/0ga kit (although I am super cheap), I have already bought my 1/0ga wire kit, but it is so inflexible, so big and thick, its extremely difficult to use in my install. That is not saying I am not going to use it. I'm just trying to *think* about this logically, you know?


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## Oliver (Jun 25, 2007)

hypothetically you are all set


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## savagebee (Sep 12, 2006)

I always use the largest cable that I can fit into the terminal. I used to due so because I thought I had to in order to let the amp perform properly, now I do it because Im paranoid. In your situation I wouldnt be that worried about it.


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## blamus (Mar 9, 2009)

a$$hole said:


> hypothetically you are all set


And that's why I am asking, hypothetically I am fine, but have I missed something practically? Does it actually work in real life?


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## emperorjj1 (Sep 10, 2008)

you should be fine running 850w at either 2 or 4 ohms off of real 4g wire with good connections/good ground


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## chuyler1 (Apr 10, 2006)

From the BCAE site...

Wire Gauge - Recommended Maximum Fuse Size
00 awg - 400 amps 
0 awg - 325 amps 
1 awg - 250 amps 
2 awg - 200 amps 
4 awg - 125 amps 
6 awg - 80 amps 
8 awg - 50 amps 
10 awg - 30 amps

If you're not sure how much amperage you are running, consider this: Most car alternators only output about 120-150 amps. If you have serious light dimming issues and your battery won't stay charged while you listen then you could be pushing the limits of your alternator (and your hearing). Otherwise, you are probably fine with 4ga wire (real 4ga, not the walmart kind) since there is no way you are sustaining more than 125 amps for more than a few seconds at a time.

As for voltage drop, 90% of the amps on the market today have some sort of regulated power supply which means they should produce the same power at 13.8v as they do at 12.5v. A 0.2 loss in voltage across a 20 ft wire isn't going to make for an audible difference traveling at 60 mph. It might make a difference in the lanes of your local SPL sound-off though so it depends on what your goal is.


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## cubdenno (Nov 10, 2007)

I never condone running undersized. There are a couple of topics on this site regarding the myths regarding the big 3 upgrade and in one of those i think Andy W. (JBL) mentions what it takes to blow a 300 amp fuse. Scary.

Anyway,I think if you amp clamp your setup, you will find that do to Impedance rise, you will come to find that you are going to be pulling significantly LESS than you think. I know I was surprised when I checked mine. i use 1/0. I found during a tone test when I was figuring out actual power, impedance rise and amp efficiency. I found that 4 gauge would have been acceptable with what was actually being pulled. 

Unless you are running multi kilowatts of power CCA is perfectly fine. I did find that system voltage drop was reduced by running a separate same gauged negative lead from the battery than by grounding to the chassis.


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## goodstuff (Jan 9, 2008)

Fire.


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## cubdenno (Nov 10, 2007)

goodstuff said:


> Fire.


Hee heeeeee


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## goodstuff (Jan 9, 2008)

cubdenno said:


> Hee heeeeee


Funny till it happens. Would not be that big of a deal if it wasn't surrounded by flammable materials ( carpet, fabric, seats, humans, etc).


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## bird333 (May 28, 2008)

Worst case scenario, you could start a fire in your car.


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## sqshoestring (Jun 19, 2007)

The Drake said:


> Are you serious? Why in the world are we spoon-feeding people?
> 
> Do some research, its really not that hard. Here is a site for starters:
> 
> Basic Car Audio Electronics


The voltage drop and heat from resistance (two different things) can be mathematically figured if you know or measure the draw. There are charts there that show it and calculators to punch in your load at the above site. A class D will take less power than class AB. Note you will have to play your amp at clipping levels to draw the max amount, the amp will draw much less at 3/4 volume. To put it simply you get voltage drop over distance more than anything, a smaller wire will carry more current for a short distance with no drop. But either can be over drawn and heated, in particular the smaller one. Note that a lot of cheap 700-1200w amps are really like 110x2 and max at 360x1rms, yet a class D will take maybe 1/3 less power depending.

I clamped my kicker zx700.5 running four doors at 4 ohm and four 12s at 2 ohms and clipping the subs it peaked at 74A, was much less RMS. The 420rms sub section is class D, highs 4x70 and they were near clipping too. It is running on a 5ga Scoche Walmart kit with a 100A fuse. But I forgot to check voltage at the amp for drop, my HU showed 13.5+ car at idle. It should be enough wire for it by the charts for .5v drop. On top of that I never play it that loud because you can't even hear the doors when the subs near audible clipping. Yeah the subs can take 600 so even clipping they don't move a whole lot running IB.

The fuse at the battery helps to keep the flames away, I would not run a huge one unless you had to.


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## goodstuff (Jan 9, 2008)

bird333 said:


> Worst case scenario, you could start a fire in your car.


The car could be in your garage and catch your house on fire. Or be in a parking lot next to other cars and catch them on fire when it blows up. or on the freeway. nothing to **** with. spend more time on this than you want to.


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## cubdenno (Nov 10, 2007)

goodstuff said:


> The car could be in your garage and catch your house on fire. Or be in a parking lot next to other cars and catch them on fire when it blows up. or on the freeway. nothing to **** with. spend more time on this than you want to.


Of course this happens if you don't fuse. 

Also the odds with a standard aftermarket system are low as what is pulled while listening to music. If you were playing continuous white noise at max volume with the amps at clipping then yes you need to be careful.

I am not entirerly convinced this would happen without some serious bad luck on your average aftermarket system.

Again, I am not a proponent for going against wiring guidelines. 

Tell you all what, my son's car got hit today so I am pulling the boys amp (Sundown SAE1000D) and his subs to put into my wifes Suburban which has an 8 gauge wire run to the back. 30 amp fuse. I will see if I can blow the fuse. I am sure at 1 ohm dcr but I am going to wire it at a 4 ohm dcr to safeguard for a daily driver. Will let you all know.


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## emperorjj1 (Sep 10, 2008)

wait what your seeing if a 1000d will blow a 30a fuse at 4 ohms?

if it makes u feel better i had a T30001bd wired at 1 ohm on a 150a fuse for a few weeks before blowing it. ive also blown a 30 or 40a fuse with a T10001bd, T5002, T5001bd

not sure how that helps anything as i said before the quality of the wire means more then what its called


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## goodstuff (Jan 9, 2008)

cubdenno said:


> Of course this happens if you don't fuse.
> 
> Again, I am not a proponent for going against wiring guidelines.


I wasn't trying to come across as a hard ass, gotta make sure people understand how to be safe.


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## Pseudonym (Apr 17, 2006)

Read this.


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## Hokieron (Mar 22, 2009)

Just think of the heavier wire in the same way as health insurance. You might not ever "need" it, but if something catostrophic happens, it sure will be nice to have it in place jmho...


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## sqshoestring (Jun 19, 2007)

I ran a SS rubicon 302 at 4 ohm mono on an 8ga off the fuse box in my car, lol It worked great. Was it dropping voltage? I have no idea. Did it melt the wire? No way. Did I beat it hard? Sometimes. Yes it was a temp setup when I had a problem with the other amp, went louder than the other 300w amp too that thing really puts out.


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## Franklin Stien (Jul 17, 2009)

I've been witness to more than one car fire due to improper power/ground wiring techniques and substandard (cheap or too small guage) wiring. If you are feeling lazy you might as well go all the way and leave the baby amp hooked up to the small guage wire. You can talk "what about this, what about that" all day, but when you are calling 911 to put your car out it will be too late to get on the ball.


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## cubdenno (Nov 10, 2007)

goodstuff said:


> I wasn't trying to come across as a hard ass, gotta make sure people understand how to be safe.


Hey man, no worries!!

I treat it all like I want to be interpreted. There is no doubt I am understood when I want to be any type of ass (hard, dumb, jack, hole etc).


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## Franklin Stien (Jul 17, 2009)

And just for the record, yes I did get up on the wrong side of the bed today:mean:


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## cubdenno (Nov 10, 2007)

Can there be an electrical fire due to improper gauging of wire? Absolutely. We all have stories of the "worst case scenario" that can happen. 

I would bet that most electrical fires from a power wire run from the battery to the trunk are from improper fusing rather than improper gauging. Most people are just not going to be putting that serious of a strain. It takes a tremendous amount of time with a serious overdraw of current to melt an 8 gauge wire let alone a 4. This is like the big 3 argument. It will have no end. 

It's your car. be responsible. You know your listening habits. Do what protects your car and your property. If following the standards for wire runs makes you the most comfortable, then follow it. If in knowing your listening habits, you feel that there is no way in hell you will ever touch the max current draw of your system, then gauge that wire accordingly.

I still say that most people will be surprised to find that their total system draw playing music is under 50% of what they think during music playback...


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## Franklin Stien (Jul 17, 2009)

Well said cubdenno, all pertinent information to the OP has been dispensed. Just remember; it will never hurt you to get your butt off the couch, err on the side of caution, or spend a couple extra bucks to go the extra mile...or something like that.


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## MarkZ (Dec 5, 2005)

Hot wires? Are you people serious?


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## Franklin Stien (Jul 17, 2009)

Usually hot ATC fuseholders on cheap 10ga. to 8ga. amp install kits that are hooked up to heavily loaded amplifiers. Giving you a stinky wad of hot melted goo with a perfectly good 30 amp fuse still passing current inside.


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## dingaling (Apr 14, 2005)

blamus said:


> What are the actual problems of using wires that are too small?


hmm...she'll complain and then just laff at you 

ok me not funny


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## Franklin Stien (Jul 17, 2009)

now that there is funny as H-E-doubletoothpick:laugh:


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## Franklin Stien (Jul 17, 2009)

So the final verdict is that she will laff at your small wire producing a melted wad of stinky hot goo. I guess I'm going with the biggest cable I can possibly produce.


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## sqshoestring (Jun 19, 2007)

Franklin Stien said:


> Usually hot ATC fuseholders on cheap 10ga. to 8ga. amp install kits that are hooked up to heavily loaded amplifiers. Giving you a stinky wad of hot melted goo with a perfectly good 30 amp fuse still passing current inside.


Did that back in the 80s when larger holders/fuses were hard to find. The solution is to fill the holder with vaseline, insert fuse, tape or cover the entire holder from weather. This providing you are not overdrawing it, I had a 20A on one amp and a 10A on the other in the trunk. I would blow the 30A every month or so however, likely I was abusing it, but it melted from corrosion even though it looked ok. With the grease in it they did not melt, they did not melt when new....for a while.


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## Drop2Flat (Oct 30, 2021)

chuyler1 said:


> From the BCAE site...
> 
> Wire Gauge - Recommended Maximum Fuse Size
> 00 awg - 400 amps
> ...


 Thank you for posting the most logical explanation of why using HUGE power wires on a stock alternator doesn't make sense! Obviously power starts from the engine, not the amplifiers. If the engine doesn't put out more than 120-150 amps, a larger power wire doesn't provide any benefit. Good info!


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