LFP using Welding cable (wire-classes) and ampacity; Quattro 10kVa

[SolarF9]

This thread and overall inquiry is about the reality of 4/0 welding cable's amp ratings of the different classes on the market.

This is in relation to high capacity LFP cabinets, bus bars, Victron 10kva Quattros and energy transfer.

Does anyone know why..... AND/or if it's true.. that...

"Ultra-Flex" cable for welding (orange with black stripe) has more ampacity than...
"M-class" (all orange)...
or...
"K-class" (typical/normal welding cable)????


Ie
4/0 (for let's say)...
50 ft & 600vdc:
• Ultra-Flex... 600amps
• M-class.... 405amps
• K-class... 310amps

That's what the literature has on amps for each class product in the few places i looked.

I know that wire strand count goes up in each class. And i think the insulator also gets a tweak.

But does it really increase amperage abilities (again 50ft max run and all things equal)?

I think...
4/0 Ultra-Flex may have the highest strands (based on 2/0)... X,xxx of 34awg
(... no ref for 4/0,,, but 2/0 is 3,087 at 34 awg)

4/0 M has next highest (i aSSume).... 5,225 strands of 34awg

4/0 K has the least of the three... 2,054 of 30awg


Is this all just marketing hype/gimmicks?

Thanks in advance!


------
update 3/3/24

Also was just told by one distributor of the USA made M-class that the amperage rating is only an "intermittent" rating.

They contacted the manufacturer.

They did not (would not) associate a time at that amperage.

I assume ALL welding cable works that way... Only the max intermittent rating published.

 

[1201]

so even if its labeled 4/0 the ampacity can be different?

 

[Brucey]

Is UL listing a requirement? If so I'd prob go with this:

0000 Gauge (4/0 AWG) Battery Cable with Ends OFC Copper Flexible Stranded UL MTW/THW/SGT

www.batterycablesusa.com

 

[SolarF9]

Hello.

Thanks gents!!!


From what i just learned...
The K and M class definitely have different ratings, jackets, temp ranges and amp ratings. Each have their place in desired locations, builds and legalities (yada yada yada stuff)


the Ultra-Flex is actually a name-brand version of M-class cable.

I do not believe that company makes 4/0. Only up to 2/0 in that class.

As far as standards...
Their spec sheet (with listing pedigrees) is here:

https://www.directwire.com/wp-content/uploads/2023/09/DIRECT-Ultra-Flex-Welding-Cable-Spec-Sheet-R08-23.pdf?x73669

They do make 4/0, but it is a K-class (named Flex-a-Prene), but has a tweak in it i guess to also make it a name-brand stand-out/option.

It's standards are:

• SAE J1127 Compliant (#6 to 250 MCM)
• NEC Article 630 (Electric Welders)
• Suitable for battery use per UL 558 and 583
• REACH, RoHS, CMRT, and Prop 65 Compliant

Another site has both K, & M.... in addition to the name-brand (Ultra-Flex).


From that site...
M-class and K-class spec sheets:

Welding Cable - By the Foot and By the Spool

Shop a wide selection of flexible copper welding cable at low prices with fast shipping - available by the foot with no cut charges, or by the spool.

www.wireandcableyourway.com

As i hastily doodled around, it appears some of the K-Class cable is only RoHS standard/compliant; but not all.


M-class (from site above) will have an array of standards attached to it...
UL Listed
CSA Certified
MSHA Approved
Meets UL Vertical Flame Test per UL 854
RoHS Compliant


The Ultra-Flex has:
Meets SAEJ1127
National Electrical Code article 630 electric welders
Rugged jacket and highly flexible
Resits Abrasion, Cut, Tear, Ozone, Flame, Grease, Oil, Water, Acid, Diesel, and Gas
Halogen free and Ozone resistant
Sequentially marked
Custom indent available
Made in USA



Seems the Ultra-flex has more strands at a thinner gauge than the M (&def K) with a tweaked jacket. Cost is considerable more.

i also think i read (generally) that "battery cable" is considered K-class (at least the link above), and... has a different jacket (PVC) than Welding cable (EPDM).... Fwiw.

In the end, i THINK the EPDM jacket and higher strand count in M-class allows it to go to the higher amp ratings... as long as it is in open air... Not in configure/hot place ( i think).

Now back to the bat cave for a nap. Worked all night.

again... THANKS.

 

[SolarF9]

update 3/3/24

Also was just told by one distributor of the USA made M-class that the amperage rating is only an "intermittent" rating.

They contacted the manufacturer.

They did not (would not) associate a time at that amperage.

I assume ALL welding cable works that way... Only the max intermittent rating published.

 

[OffGridForGood]

This is in relation to high capacity LFP cabinets, bus bars, Victron 10kva Quattros and energy transfer.

50 ft

K-class... 310amps

Interesting read.
In DIY Solar, are we most concerned with peak or continuous amperage rating, - I say continuous.
50 - feet ? Keeping the Inverters close to the ESS is a common build design, since large DC cables are sensitive to distance - as are costs. Max cable length should be less than 10-feet for most set ups. (yes?).

As my own ESS got bigger, I built the battery banks into two, each supply the main Pos and Neg bus to the inverters with separate 4/0 standard welding cables. ie as the ESS gets bigger, and could exceed 300A, split into two each with it's own cables, fuses and disconnect.
It is not just the cable amperage that becomes an issue, but also getting proper DC breakers, fuses, etc to carry more than 300A, and what these will cost.
Two ESS cabinets feeding a main pair of Pos/Neg buses lets you take one offline to do work on it, while the lights remain on from the other.

 

[SolarF9]

50 - feet ? Keeping the Inverters close to the ESS is a common build design,

Hello.

Thanks for the input.

The 50ft length was used because that's seems to be a common number the manufactures of welding cables use in their spec sheets

As for my build...
NOT exactly diy at the module level.

My modules each have a PACEex BMS with an ON/OFF switch and a built-in breaker. They also appear to be SOK knock-offs w/ganfeng LFP (not my choice but rather what was there where delivered). I also have 16 cells to start a true DIY REC or Batrium build. Exact cells as in the modules.

Cables:
I'm sizing that and T-fuses for:

• the paralleled modules max output,
• the linear length to the bus-bars and then to the inverters,
• voltage, and
• the cable rating itself.

Cable manufacturers:
Was asking different manufacturers for tech info on specs, they just directed me to their spec sheets.... Which usually has 50ft as the shortest run.


Going to the Sales peeps:
When asking a couple distributors, i got the spec sheet again... and later (after more questioning) a generic "intermittent" reply.

I was hoping for "continues or 100% duty" cycle (rating). Interesting to see the manufactures not stepping up... or is it?



So... imho... taking the most prudent route.

1. Sizing and T-fusing for K-class welding cable.
2. But... using M-class cable (to provide more flexibility in the cabinet and ampacity)
3. Looking at DC rated *breakers and wincing at the prices instead of a basic DC kill switch (on/off)... or using the hi-voltage/amp switches for DC.
4. Maybe also fusing at the Lynx Distributer bus-bar with 70v mega-fuses (was told i need a 20% amp buffer from manufacture for longevity degradation and again nuisance tripping).

*Main ON/OFF switch
(After the bus-bar and going to the inverter:
I noticed some 50k AIC dc breakers (higher than 20k aic T-fuse), but would have to have two ganged paralleled together to provide protecting without nuisance tripping. I think that works????

 

[S Davis]

I only use DLO cable and cast lugs it is expensive but made for harsh applications. The acceptable bend radius is really good.

4/0 Diesel Locomotive Cable 2KV

Diesel Locomotive Cable. Cut to length - sold by the Foot.

www.wireandcableyourway.com

 

[SolarF9]

I only use DLO cable and cast lugs it is expensive but

Thanks.

I guess I've not read enough...
I've only heard of a supplier of cast lugs (looking at 90deg elbow/hockey-stick bend from Remy)... and one other local fella mention cast lugs. I've never done that. Is that common on BESS builds?

As an aside... casting...
Ive read that Spelter sockets, for steel wire cable ends, used in guy wires (for things like lattice towers, etc) strongly urge using a pro to do the molten stuff.

As a further aside to the last aside,,,, think they can also use an epoxy with some of the socket ends.

Do you have any good resource links that show how to set-up and execute a proper casting for a hi-temp (shorting occurrence)... hi-v and hi-a use? I'm even more clueless than usual on this....

Hmmm... now that you brought it up giving me a second look... Think i will contact that supplier of cast lugs. He's got to have links/resources.

 

[Sennen]

I use Temco for my wires and lugs.

There's a difference between short term usage (Welding/Chassis wiring) and power transmission (constant power delivery)
Example: A starter motor in a car can draw upwards of 150-200 amps. The manufacturers typically toss a 4ga on that and call it good. For a short duration, that's deemed a-ok. If they were constantly running 150-200 amps through a 4ga wire, you'd be cooking it.

 

[ricardocello]

I have 10' of Class K 4/0 from Battery Rack to Inverter Rack 600A Bus Bars, with 300A Class T fuse in the Battery Rack.
It is EPDM insulation rated at 90 deg C, and "310A Ampacity", which I assume is the current needed to heat that cable to 90C!
The Class T prevents doomsday, hopefully.

So 4/0 wire resistance is typically around 0.18 milliohms/ft. Power = I^2R, so at 300A continuous, each foot of cable would dissipating 16.2W!
So my 10 ft length would be dissipating 162W. Sounds pretty dangerous.

EDIT: I read the table wrong, it is 0.05 milliohm per ft, so only about 5W per foot. Sounds only 1/3 as dangerous, thanks @DougfromdaUP

In any case, I never expect continuous power that high through the cable, because the other fuses in the system would have already blown.
And a dead short will hopefully blow the Class T.

 

[DougfromdaUP]

I have 10' of Class K 4/0 from Battery Rack to Inverter Rack 600A Bus Bars, with 300A Class T fuse in the Battery Rack.
It is EPDM insulation rated at 90 deg C, and "310A Ampacity", which I assume is the current needed to heat that cable to 90C!
The Class T prevents doomsday, hopefully.

So 4/0 wire resistance is typically around 0.18 milliohms/ft. Power = I^2R, so at 300A continuous, each foot of cable would dissipating 16.2W!
So my 10 ft length would be dissipating 162W. Sounds pretty dangerous.

In any case, I never expect continuous power that high through the cable, because the other fuses in the system would have already blown.
And a dead short will hopefully blow the Class T.

The tables I look at Show a much lower resistance for 4/0, around .05 milliohm per foot, giving you about 5 watts loss per foot at 300 amps.

 

[ricardocello]

The tables I look at Show a much lower resistance for 4/0, around .05 milliohm per foot, giving you about 5 watts loss per foot at 300 amps.

Well, that’s encouraging. Next time I’m pumping 200A through them I’ll try to measure the actual voltage drop, and calculate the resistance.

I just looked at several other tables and I see 0.05 milliohm/ft too. My error, need reading glasses next time, thank you!

 

[Zwy]

Thanks.

I guess I've not read enough...
I've only heard of a supplier of cast lugs (looking at 90deg elbow/hockey-stick bend from Remy)... and one other local fella mention cast lugs. I've never done that. Is that common on BESS builds?

I have that lug on my bank and ordered extras too. Heavier lugs used on starting cables for Class 8 trucks use the same type lugs. These crimp just fine, back in the day I used the large pliers crimper, now I use Temco hydraulic. I believe I started with the oversize dies but can't recall if I stepped down on the crimp.

As an aside... casting...
Ive read that Spelter sockets, for steel wire cable ends, used in guy wires (for things like lattice towers, etc) strongly urge using a pro to do the molten stuff.

As a further aside to the last aside,,,, think they can also use an epoxy with some of the socket ends.

Do you have any good resource links that show how to set-up and execute a proper casting for a hi-temp (shorting occurrence)... hi-v and hi-a use? I'm even more clueless than usual on this....

Hmmm... now that you brought it up giving me a second look... Think i will contact that supplier of cast lugs. He's got to have links/resources.

 

[S Davis]

That is the same crimper I use, 4/0 from yesterday. Ok

24” 4/0 DLO rated 405amps cost:$37.00 without figuring any shipping for materials.

 

[SolarF9]

Thanks gents

Looking into it.