How to Calculate Wire Size.

[Chriszle 10+ year member]

Car Audio Wiring: Power Wire & Speaker Wire

Link to a wire gauge chart given length of wire. It is funny how the rating does not give a specified length of wire, that is one of the crucial components in determining how much current it can handle. The others being the resistance of the wire and its size. We can go in circles man.

 

[Chriszle 10+ year member]

And just go hit the 4 gauge big 3 idea one last time. If you leave the stock wiring in place and add 4 gauge, you greatly increase the 300 amp current that it can handle safely (depends again on wire length, size, resistance).

 

[bubbagumper6 5,000+ posts]

Car Audio Wiring: Power Wire & Speaker Wire
Link to a wire gauge chart given length of wire. It is funny how the rating does not give a specified length of wire, that is one of the crucial components in determining how much current it can handle. The other being the resistance of the wire. We can go in circles man.

That chart doesn't say anything about 4 gauge being able to handle 300A. I agree that wire length has a great impact on the situation but the reality is, if your running over 200A you should be using 1/0 not 4 gauge.

If you go below the 300 circular mills/amp threshold you risk overheating the wire at load and melting the insulation, regardless of how long the wire is.

I suggest you return to the page I linked and do a bit of reading (learning).

 

[Cabin_Pressure 10+ year member]

Thats gravy bro, now that we are on the same page. A 4 foot run of average 4 gauge wire can carry 300 amps of current and drop .3 volts.

Lol, try it continuously. You should REALLY stop making these suggestions. There is a factor you seem to be totally overlooking, it is called thermal de-ration for cable current rating. Your chart may need some help, try using the AWG chart for amperage rating of conductors. That is the industry standard for cable sizing for a given current draw. Also, could a mod please delete this thread? It is should not be considered informational or a "How to" at all. It is someones mis-interpretation of reasonable wiring methods.

 

[Cabin_Pressure 10+ year member]

face/palm to the OP

 

[Chriszle 10+ year member]

That chart doesn't say anything about 4 gauge being able to handle 300A. I agree that wire length has a great impact on the situation but the reality is, if your running over 200A you should be using 1/0 not 4 gauge.
If you go below the 300 circular mills/amp threshold you risk overheating the wire at load and melting the insulation, regardless of how long the wire is.

I suggest you return to the page I linked and do a bit of reading (learning).

I admit, that I did not calculate for the wires temperature change when being pushed to its limits. On a lesser point, most car audio systems do not draw 200 amps of current, so I will stick by my words.

 

[bubbagumper6 5,000+ posts]

I admit, that I did not calculate for the wires temperature change when being pushed to its limits. On a lesser point, most car audio systems do not draw 200 amps of current, so I will stick by my words.

Your grasping at straws man, just pack it up and call it a day. Accept the fact that you still have a lot to learn and move on.

 

[Chriszle 10+ year member]

Ok. Here comes my last stand. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif. The chart I use for all my calculations is right here. http://www.powerstream.com/Wire_Size.htm All my calculations have been based on the 700 circular mils per amp rule which is quite conservative. 1000 ft of 4 gauge wire has 0.2485ohms of resistance, therefore calculating for a 4 ft run the resistance in the wire equals ~.001 ohms. When calculating circuits, complex circuits, such as an alternator and many batteries, in order to put it simply, you need to break it down into seperate circuits as each time there is an additional power source the numbers will change. Simlilarly, the NEC states that in any given circuit a voltage drop of 3-4 percent is acceptable. This means that any any given length of wire at 10 volts a drop of .3 volts is acceptable. Now the alternator supplies ~14 volts (to make calculations easier). 3 percent of 14 volts yields a drop of .42 volts safely within the capacity of the wire. While I realize the wire will heat up, I feel that the 700 circular mills per amp is a very safe starting point considering it is over double the recommended safe limit.

 

[bubbagumper6 5,000+ posts]

Ok. Here comes my last stand. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif. The chart I use for all my calculations is right here. American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies All my calculations have been based on the 700 circular mils per amp rule which is quite conservative. 1000 ft of 4 gauge wire has 0.2485ohms of resistance, therefore calculating for a 4 ft run the resistance in the wire equals ~.001 ohms. When calculating circuits, complex circuits, such as an alternator and many batteries, in order to put it simply, you need to break it down into seperate circuits as each time there is an additional power source the numbers will change. Simlilarly, the NEC states that in any given circuit a voltage drop of 3-4 percent is acceptable. This means that any any given length of wire at 10 volts a drop of .3 volts is acceptable. Now the alternator supplies ~14 volts (to make calculations easier). 3 percent of 14 volts yields a drop of .42 volts safely within the capacity of the wire.

I just have to say that a 12v DC car electrical system is far from a complex circuit...

 

[Cabin_Pressure 10+ year member]

Ok. Here comes my last stand. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif. The chart I use for all my calculations is right here. American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies All my calculations have been based on the 700 circular mils per amp rule which is quite conservative. 1000 ft of 4 gauge wire has 0.2485ohms of resistance, therefore calculating for a 4 ft run the resistance in the wire equals ~.001 ohms. When calculating circuits, complex circuits, such as an alternator and many batteries, in order to put it simply, you need to break it down into seperate circuits as each time there is an additional power source the numbers will change. Simlilarly, the NEC states that in any given circuit a voltage drop of 3-4 percent is acceptable. This means that any any given length of wire at 10 volts a drop of .3 volts is acceptable. Now the alternator supplies ~14 volts (to make calculations easier). 3 percent of 14 volts yields a drop of .42 volts safely within the capacity of the wire.

Wow, you figured the resistance of 4 AWG wire.......good job.

 

[Chriszle 10+ year member]

I never once advocated trying to scrape by with the bare minimum. Perhaps I need to explicity state that this is just a good calcuation to start from, outside tempterate, insulation thickness, thermal conductivity, wire temperature, and air convection all do come into play when looking at these figures.

 

[bubbagumper6 5,000+ posts]

I never once advocated trying to scrape by with the bare minimum. Perhaps I need to explicity state that this is just a good calcuation to start from, outside tempterate, insulation thickness, thermal conductivity, wire temperature, and air convection all do come into play when looking at these figures.

again...

Your grasping at straws man, just pack it up and call it a day. Accept the fact that you still have a lot to learn and move on.

 

[Chriszle 10+ year member]

Wow, you figured the resistance of 4 AWG wire.......good job.

If you need me to explain why this is important I will finish the statement. In order to cause a .42 volt drop in a circuit with a resistance of .001 there must be sufficient current. The formula is Current = voltage drop/resistance. .42/.001= 420 amps. I think my 300 amp rating is more then safe for a 4 foot run. As far as the 700 circular amps/amp quote, thats funny because right above it was stated that going under 300 circular amps is dangerous.

 

[bubbagumper6 5,000+ posts]

If you need me to explain why this is important I will finish the statement. In order to cause a .42 volt drop in a circuit with a resistance of .001 there must be sufficient current. The formula is Current = voltage drop/resistance. .42/.001= 420 amps. I think my 300 amp rating is more then safe for a 4 foot run. As far as the 700 circular amps/amp quote, thats funny because right above it was stated that going under 300 circular amps is dangerous.

You are correct, I was mistaken at that point, 700 circular mils/amp is fine (overkill, but fine). However, I'm not sure why your still arguing that 4 gauge can handle 300 amps seeing as that violates your own criteria.

 

[Cabin_Pressure 10+ year member]

You are correct, I was mistaken at that point, 700 circular mils/amp is fine (overkill, but fine). However, I'm not sure why your still arguing that 4 gauge can handle 300 amps seeing as that violates your own criteria.

He can't read the column in the chart that has the specs for 4 AWG?