4/0 cable: Pushing Over the Current Limit

[EPicTony]

I have 21kw of PV and 3 EG4-6000xp inverters. I have a battery bank of 14 rack mount 100Ahr batteries connected with 4/0 cables (length of 10'.
Originally I limited the charge current to 230A which is the rating on the 4/0 cable.
It gets warm but not hot @ 230A.
I'm wondering how much I can push over the 230A rating ?
I want to charge the batteries faster during party cloudy conditions here in NE Ohio.
I have tried 250A and now I'm up to 270A. It gets warmer but I can still hold my hand on the wires (140deg F) now, so nothing is going to start smoking.
How hard can I push the 4/0 ??. I want to get up to 30A/battery but that would be 30x14=420A (probably too much).

 

[sunshine_eggo]

Are you sure the cable is only rated for 230A? Actual UL battery cables are rated to 445A outside engine space, 378A inside engine space:

Custom Battery Cables with Ends - Flexible UL Listed Wire

www.batterycablesusa.com

I would not go beyond the rated current.

 

[EPicTony]

Are you sure the cable is only rated for 230A? Actual UL battery cables are rated to 445A outside engine space, 378A inside engine space:

Custom Battery Cables with Ends - Flexible UL Listed Wire

www.batterycablesusa.com

I would not go beyond the rated current.

Got it from a general ampacity chart...... if it is 445A I'm good to go !!!!!

 

[hwy17]

You could tell yourself that you get to use the NEC free air table, if you think it applies.

 

[sunshine_eggo]

Got it from a general ampacity chart...... if it is 445A I'm good to go !!!!!
View attachment 260267

Do your cables have a temperature rating on them?

Free air rating of 4/0 with 90°C insulation is 405A.

The question is what are YOUR wires rated for?

 

[EPicTony]

sunshine_eggo: Looked over the chart on your link, 445A it is for 4/0 cable. Wow I'm happy. I was thinking I had to add more cables. Sweet!​

 

[crossy]

You need to check the spec. of your actual cable. The NEC ratings are somewhat conservative.

@sunshine_eggo beat me to it

We've shoved 270A down 95mm2 with no issues whatever. Your actual heating points will be your crimp and lug connections.

A decent thermal imager is a dead handy thing to have, phone plug-in ones are not hideously expensive. We have a Mileseey TR256i which is more than adequate.

 

[robbob2112]

105c rated welding wire or DLO is 440amps, but THHN rated 90c is 260amps...

You need to read the labels on your cables and see what the temperature rating is

 

[EPicTony]

Do your cables have a temperature rating on them?

Free air rating of 4/0 with 90°C insulation is 405A.

The question is what are YOUR wires rated for?

Chart is showing 550A !!!!!!!!!!!!!!!!!!!!
SAE BATTERY/Welding Cable - GAUGE COPPER WIRE BATTERY
Highly flexible annealed 30 gauge bare copper conductor, insulated with an EPDM RUBBER jacket and paper separator. Operating temperatures range from -50°C to +105°C (-58°F to +221°F). Rated to 600 volts
• Resists Abrasion, Cut, Tear, Flame, Grease, Oil and Water
• RoHS Compliant.
Rugged jacket and highly flexible Rubber EPDM Jacket.

 

[sunshine_eggo]

sunshine_eggo: Looked over the chart on your link, 445A it is for 4/0 cable. Wow I'm happy. I was thinking I had to add more cables. Sweet!​

That's for 105°C rated UL 1426/Marine wire.

Please confirm your insulation rating before you go crazy with things...

 

[sunshine_eggo]

Chart is showing 550A !!!!!!!!!!!!!!!!!!!!
SAE BATTERY/Welding Cable - GAUGE COPPER WIRE BATTERY
Highly flexible annealed 30 gauge bare copper conductor, insulated with an EPDM RUBBER jacket and paper separator. Operating temperatures range from -50°C to +105°C (-58°F to +221°F). Rated to 600 volts
• Resists Abrasion, Cut, Tear, Flame, Grease, Oil and Water
• RoHS Compliant.
Rugged jacket and highly flexible Rubber EPDM Jacket.
View attachment 260269

We posted at the same time.

Welding cable is essentially the same thing as battery cable, but it's intended for short burst operation, not sustained, and it can tolerate much larger voltage drops. You don't want to use their ratings. I think you're good to the 445A, but I would sneak up on it, preferably with the aforementioned temperature measurements.

 

[EPicTony]

That's for 105°C rated UL 1426/Marine wire.

Please confirm your insulation rating before you go crazy with things...

Checked it: 600V, 105degC welding cable. Happy I don't have to spend more $$$ this solar is getting expensive

 

[sunshine_eggo]

Checked it: 600V, 105degC welding cable. Happy I don't have to spend more $$$ this solar is getting expensive

Yep. At a minimum, those should meet the 405A free air rating. Again... sneak up on it...

Let's see... 30A * 14 batteries = 420A

Whew... that's a lotta joose.

 

[time2roll]

How about split the bank of batteries into two stacks of seven. Feed each with 230 amps from the common bus.
One more battery would go three stacks of five bringing the rate to 690 amps. Need a bigger bus.

 

[robbob2112]

One note - unless it says UL listed on the side of the cable it isn't and won't pass an inspection.... welding cables is fantastic wire but not typically UL listed.

 

[Bluedog225]

Assuming in the neighborhood of rated current, how hot are folks willing to run a wire?

E.g.: max it out at 150 F at “full tilt” conditions?

Or something lower?

 

[k490]

My 12k Winch on my jeep I have 1/0 wire from batterycables USA Extreme copper gets very warm pulls about 300-350 amps under heavy loading still way under 105C which is 221F. I think this wire can go higher then the rating I wouldn't with an inverter setup. They do sell UL rated version of this this is the automotive rated version.

 

[hwy17]

Assuming in the neighborhood of rated current, how hot are folks willing to run a wire?

E.g.: max it out at 150 F at “full tilt” conditions?

Or something lower?

I would chicken out at 60c/140f for any wire I think no matter the rating.

For DC stuff. For AC I just follow the NEC and don't go feeling it.

 

[sunshine_eggo]

If I can hold my hand on it, it's not too hot. After that, I'm going to need an IR thermometer.

 

[time2roll]

Most adults will suffer third-degree burns if exposed to 150 degree water for two seconds. Burns will also occur with a six-second exposure to 140 degree water or with a thirty second exposure to 130 degree water. Even if the temperature is 120 degrees, a five minute exposure could result in third-degree burns.

Stick with 230 amps for long battery charge. 430a is fine for surge performance.

 

[Danke]

From Windy Nation

 

[robbob2112]

Most adults will suffer third-degree burns if exposed to 150 degree water for two seconds. Burns will also occur with a six-second exposure to 140 degree water or with a thirty second exposure to 130 degree water. Even if the temperature is 120 degrees, a five minute exposure could result in third-degree burns.

Stick with 230 amps for long battery charge. 430a is fine for surge performance.

One thing, water transfers heat much faster than air..on the order of 20 times faster... and it makes total contact verse just a touch.

Telecom equipment is allowed to hit 140f before we start shutting things down.

 

[robbob2112]

From Windy Nation

So here is a question - do you really want a 221f wire around? Meaning if you intend running wires hot you have to take into account what it is touching. You could melt plastic or soften it if it is a shelf support that could be trouble.

 

[Bluedog225]

Did I read you right OP that you were at 270A and140 deg F?

 

[sunshine_eggo]

Math time...

400A through 20' of 4/0 is seeing 1mΩ of resistance and generating 157W of heat. That's 2.5X 60W incandescent bulbs being pumped into 13# of copper that has 20 linear feet worth of surface area (346 sq-in) from which it's dissipating that heat.

Can we all put our vajeens away now?

I'm voting for NEC open air rating of 405A or 28A per battery. Pretty close to target.

If you have an IR gun handy, check temps, so you know you're under 105°C, especially at the lugs/crimps.