Amp wire questions

6gun · Dec 27, 2018

I'm asking for some car audio wisdom here. I'm getting ready to install a 300W Blaupunkt 8" amplified subwoofer under each seat of my '99 standard cab.

I was talking with my boss who is an electronics genius and also owned his own car radio system install shop in the 90's mentioning that I was going to pick up some 8AWG wire for the amps as outlined in the installation manual. He stated that was way oversized and to stick to 10AWG. :icon_confused:

After thinking about it, and running it through every electrical formula I have available, I realized that by all electrical laws he is correct. So my question is..... :icon_confused:

Why does the manual call for an #8 when technically a #12 would be sufficient? :dunno:

Asking purely for education, I will be using #8 anyway. :icon_hornsup:

Skirbykat · Dec 27, 2018

I'd run a single 4ga from the battery, then use fused distribution to (2) 8ga for each. Then you'll be ready if ever upgrading in the future.

Sent from my XT1585 using Tapatalk

6gun · Dec 27, 2018

That was my initial ideal. I'm just not getting the reason behind such a large wire for such a small load. #12 wire is more than enough to support 300 Watts unless I'm missing something.

Skirbykat said:
I'd run a single 4ga from the battery, then use fused distribution to (2) 8ga for each. Then you'll be ready if ever upgrading in the future.

Sent from my XT1585 using Tapatalk

Sent from my LG-H700 using Tapatalk

Ranger850 · Dec 27, 2018

Bigger wire = Less resistance. :icon_confused:

that is the only reason I could think of :dunno:

RonD · Dec 27, 2018

8ga covers the manufacturers a$$

You also have the heat factor and wire manufacturers specs

Resistance causes "heat" so wires heat up, insulation is the makers choice not the buyers, lol
Is the wire solid copper, or copper clad, or aluminum?

8ga covers the gambit of variables in DIY installations for the device manufacturer

If you do the math(amps and length) and use good wire then you can use the size you calculate as needed

Fuses need to be used on the SOURCE end of the wire, NOT the device end

i.e. Battery(12v)--FUSE------------------------------------------Device

ericbphoto · Dec 28, 2018

I would recommend no less than 10awg for each amp. 300watts would be 25amps, which 12awg should handle. But... That 300watts is probably the peak output power of each amp. Due to electrical losses, they may use more than 25 amps of input current during peak output. Furthermore, good electrical design dictates sizing your wire and fuse at 125% of rated full load current. That gets you to around 31amps. That's where I come up with using 10awg wire as long as it's not too long. And, really, how long can the circuit really get in a small standard cab pickup? That should be sufficient unless you run full 300 watts all the time. In that case, err on the side of safety and use the 8awg which will have less resistance. Therefore it will develop less heat and develop less voltage drop, therefore guaranteeing full voltage to the amp during heavy use. As wire heats up, it's resistance increases. As resistance increases in your wire, you drop voltage across the wire and your load sees less voltage. That's what wire sizing is all about.

This message composed solely of recycled electrons. Go green!

6gun · Dec 28, 2018

ericbphoto said:
I would recommend no less than 10awg for each amp. 300watts would be 25amps, which 12awg should handle. But... That 300watts is probably the peak output power of each amp. Due to electrical losses, they may use more than 25 amps of input current during peak output. Furthermore, good electrical design dictates sizing your wire and fuse at 125% of rated full load current. That gets you to around 31amps. That's where I come up with using 10awg wire as long as it's not too long. And, really, how long can the circuit really get in a small standard cab pickup? That should be sufficient unless you run full 300 watts all the time. In that case, err on the side of safety and use the 8awg which will have less resistance. Therefore it will develop less heat and develop less voltage drop, therefore guaranteeing full voltage to the amp during heavy use. As wire heats up, it's resistance increases. As resistance increases in your wire, you drop voltage across the wire and your load sees less voltage. That's what wire sizing is all about.

This message composed solely of recycled electrons. Go green!

This makes sense! I'm a service tech who does a great deal of electrical work and I take a great deal of pride in doing neat, proper work. I have no problem running #8, my boss's statement just got me to wondering so I thought I'd see what everybody else had to say on the subject.

Thanks for all the replies.

91stranger · Mar 11, 2019

300 watts aint nothing. As far as car audio goes, the bigger wire the better. That's just common sense. You can run a size 4 wire if you wanted. Wouldn't hurt anything except your eyes lol. Most of the wiring kits at stores are sufficient for basic car audio (less than 1000 watts). I don't know if you will hear those 8" speakers that well. You might though. I'm just so used to my truck (it hits hard) so it's hard to compare apples to oranges you know. Make sure your amp can breathe too. If these are self contained amps that don't have a fan then I would be sure to get as much air space as possible to keep them from over heating. I've never used an all-n-one amp/sub combo so I don't know much about those compared to a regular car audio set up (amp and subs separate). I've been known to wire up amps to factory radios and all other redneck shortcuts around things lol.

Amp wire questions

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