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1/0 gauge 300 amp rating or not?

T

troye

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Joined
Dec 14, 2023
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14
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I know there are different variables, I am just confused why there are charts online that state 1/0 is 300 amp rated, and to use a t-class 350 amp fuse, and other charts indicate it is not even close. Any help?
Here are just a few of the tables a google search comes up with that suggestion 1/0awg is rated 300amp for around 10ft runs:
https://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/
https://alternatorparts.com/wire-size-chart.html
https://wiringproducts.com/pages/battery-cable-amperage-capacity-chart

Update: i am even more confused now. People react like it will cause a fire while others post charts that support the claim from places like Windy Nation
 
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Here is some Class K welding cable 1/0.
www.wireandcableyourway.com

1/0 Welding Cable Class K

1/0 Welding Cable Class K
www.wireandcableyourway.com www.wireandcableyourway.com

It is rated at 190A, but that is at 90 degrees C!
I can’t imagine any other 1/0 would get you to 300A without seriously burning things down.

You need 4/0 for 300A, or larger.
 
troye said:
I know there are different variables, I am just confused why there are charts online that state 1/0 is 300 amp rated, and to use a t-class 350 amp fuse, and other charts indicate it is not even close. Any help?
Click to expand...
And a class-T can pass 2x rating for close to a minute.

Better to go up in voltage when amps are passing 200 - 250 amp range.
 
What is the voltage drop for 300 amps, the length of cable.
I think your significantly under sizing even with 250 mcm.

Maybe try two runs.
See how the inverter behaves if there is a measurable drop that the inverter finds objectionable then you will need to go larger still.

Now the cable is large enough not to over heat its just a question of voltage drops if they are tolerable.
Ya welding cables is probably fine...


The different tables and rating you find in a code book are mostly about cable heating.
Yes under some conditions you can use a very small cable if the insulation is rated to run hot and its in free air so it can cool itself
That's a best case...

Worst case is a cable in a conduit in a hot environment
 
troye said:
Here are just a few of the tables a google search comes up with that suggestion 1/0awg is rated 300amp
Click to expand...
All of those tables are primarily concerned with the voltage drop caused by the length of the wire,
rather than safety that the insulation will start burning.

Watts dissipated per foot is the same, regardless of the cable length.
Putting 50W 8.8W into each foot of cable will certainly heat it to unsafe temperatures.

I honestly don’t know why they are not concerned about that,
 
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time2roll said:
More like trade the 12v inverter for a 48 volt model. Maybe the OP can expand on what is connected.
Click to expand...
i got a free 12v 300ah lifepo4 (long story) so i bought a 4000watt inverter, all for fridge, chest freezer, lights and fan for hurricane aftermath. cable run will be around 5 ft.
 
OK, according to the standard AWG copper resistance tables, 1/0 cable has 0.098 millliohms/foot (apologies to the metric audience) at 20 deg C.
Power = I^2 R, so each foot of cable would dissipate about 8.8W at 300A.
copper is inside the insulation, how hot would the cable get?

So your 5 ft of cable would dissipate 44W, and there are two cables (+ and -), so 88W total coming out of those 1/0 cables at 300A.

And a total voltage drop of about 0.3 V
 
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Free air 90C conductor, table shows 260A

Wire Size Chart for Conductors in Free Air

Wire Size Chart: Allowable Ampacities of Conductors in Free Air - 30C
wiresizecalculator.net

Can of course be higher if run hotter (silicone insulation) or forced air flow.
Or intermittent, especially very short time like a starter.

I think my system would put 900A through 4/0 (3 second 44kW surge) or 500A (23kW) "continuous" only until the batteries run down (which would take about 20 minutes, so I'm not worried.) If I had larger bank I'd use dual 4/0.

That's 4x SI 6048US with 405 Ah 48V SunXtender AGM.
 
Just ignore anything from the automotive or audio world. Chassis wiring is a more serious discipline that should also be ignored.

The NEC has a free air amps rating if you want a serious reference for higher amps, and are willing to decide for yourself that your install counts as free air.
 
ricardocello said:
OK, according to the standard AWG copper resistance tables, 1/0 cable has 0.098 millliohms/foot (apologies to the metric audience) at 20 deg C.
Power = I^2 R, so each foot of cable would dissipate about 8.8W at 300A.
copper is inside the insulation, how hot would the cable get?

So your 5 ft of cable would dissipate 44W, and there are two cables (+ and -), so 88W total coming out of those 1/0 cables at 300A.

And a total voltage drop of about 0.3 V
Click to expand...
So, considering earlier you said 50w a foot would be too hot, and now you calculate 88w would result, i will likely need the 4/0, or would 2/0 do?
 
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troye said:
i got a free 12v 300ah lifepo4 (long story) so i bought a 4000watt inverter, all for fridge, chest freezer, lights and fan for hurricane aftermath. cable run will be around 5 ft.
Click to expand...
Fuse the 1/0 at 200 amps and limit the power to 2000 watts. The items listed should be under 2000w except possibly the start surge of the coolers and still that should be handled fine at this level.

Ampacity chart, these values will get the wire very hot and need 105C insulation (above the boiling point of water)
https://www.customcableusa.com/pages/voltage-drop-calculator

They also sell custom cables with professionally crimped lugs up to 4/0.
https://www.customcableusa.com/products/custom-battery-cable-marine-grade-by-the-foot
 
Lots of good information here:

diysolarforum.com

Wiring Unlimited

Wiring Unlimited is a great resource that covers many many common topics and questions relevant to DIYers. It is a free E-book from Victron Written by Margreet Leeftink. Check it out! Download
diysolarforum.com diysolarforum.com
 
Welding and battery cable from Windy Nation.
 

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Hedges said:
Free air 90C conductor, table shows 260A

Wire Size Chart for Conductors in Free Air

Wire Size Chart: Allowable Ampacities of Conductors in Free Air - 30C
wiresizecalculator.net

Can of course be higher if run hotter (silicone insulation) or forced air flow.
Or intermittent, especially very short time like a starter.

I think my system would put 900A through 4/0 (3 second 44kW surge) or 500A (23kW) "continuous" only until the batteries run down (which would take about 20 minutes, so I'm not worried.) If I had larger bank I'd use dual 4/0.

That's 4x SI 6048US with 405 Ah 48V SunXtender AGM.
Click to expand...
This is what the DLO cable I use is rated at. I would trust the 260 amp rating with this stuff.
 
ricardocello said:
OK, according to the standard AWG copper resistance tables, 1/0 cable has 0.098 millliohms/foot (apologies to the metric audience) at 20 deg C.
Power = I^2 R, so each foot of cable would dissipate about 8.8W at 300A.
copper is inside the insulation, how hot would the cable get?

So your 5 ft of cable would dissipate 44W, and there are two cables (+ and -), so 88W total coming out of those 1/0 cables at 300A.

And a total voltage drop of about 0.3 V
Click to expand...

That's better than I thought...
But i would still be inclined to use a larger a lot larger.

The duty cycle is something to consider too!
Your not going to pull 300 amps all the time.

44 watts is a considerable amount of heat for the cables to dissipate over such a short run

I used to work on a machine called a bolter that had a power cable Size #4 to supply the machine around 80 amps @ 600 volt.
The cable would get warm enough in my hand it was not pleasant to hold.. ( not that I ever thought holding cable pleasant or even while the power was on ).
This machine also had a duty cycle of about 50% and the length of cable was 150 feet.
At the machine the voltage would drop 30 volts.

All that sounds horrifying doesn't it?
Not really most machines would run just fine with a dip of 10% or less.
The cable insulation was rated to run as hot as 125c
So thats within specification.

Today however we run that same machine with a 2/0
Just because its easier to stock only that cable.
 
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