LiFePO4 prismatic cell short circuit current and main circuit protection

[Boron]

@MattiFin sadly you have shown that you are under-informed on the matter. DC systems have used blade switches since 1920+. You can see evidence of this in railway electric traction switchboards (600Vdc 1000A), Electroplating, early telephone exchanges, UPS etc.
However, and this is where your ignorance shows, Electrical power distribution and switch rooms requires operators to be specially trained, equipped full body flash suits, gloves, head googles when operating manual switch gear. There are YT vids to educate you.
On a more domestic note, the vid you showed, deliberately abused circuit breaking for clicks and drama. In reality you wear gloves to protect your hands from flash burns, wear googles to protect your eyes from UV and sparks. Its a moments operation in msecs to pull down a knife switch and the distance of separation immediately quenches the arc flash. For 12V there is no arc flash very minimal risk in auto systems. For 24V you can stick weld but the flash with quench easily within <5mm. 48 volt systems need much larger distances (I estimate 8x ) so proposition is that 50mm is a safe guideline - which I hope to demonstrate in a vid when I get all apparatus together.

Note - dc stick welding is generally ca 20V at work piece (once the arc is struck and in the CC region but starts at ca 60V to strike the arc) and 100-200 A dc. So gloves and face protection is essential but its no great drama.

Ill informed amateurs dont realise a 48V panel system pushes out full current on a sunny day and improper specified breakers may fail to cut the load in a roof fire for example (see vids of mcbs failing including a very popular one in OZ until recently banned

Here is a Vid showing positive support for hypothesis that a large knife switch will work well.

Notice the system is 48v (4 panels) in full sunlight. The arc flash is produced and sustained BUT when the distance is ca 2" it quenches. BTW you can blow the flame out or remove its heat (needed to maintain ionisation temp of ca 6000c by a simple plant mister filled with water.)

I propose also that an immediate arc fire remedy in ELV systems can use a simple plant mist bottle (as well as cable cutters)

 

[Boron]

Thats w

That is what I use. A fraction of the cost of class T but they do the job perfectly with the same AIC capability.
It just shows what a rip off Class T fuses are

FWIW I investigated this Cabal of fuse making. It is after all a piece of wire and its there to protect the installation wiring. Over current surges of 5x can be tolerated in slo-blo cases (motor starters etc). Just consult the graphs showing I^2t values.. Much of the cost of a fuse is in setting up test facilities and gaining accreditation - hence huge cost of Class T. Same applies to Siemens type NH blade fuses in EU - not nearly so expensive.

For the DID guy this is all prohibitive but a fuse link is necessary.
I found that the word "fuselink" was coined during the 30s for automobiles. You can still buy a simple wire with crimped spade terminals. Its ca 4" long with fireproof braid and breaks at ca 80A. It can be attached between the battery terminal and the distribution board, or the alternator or even the starter motor
.
Its the last resort to protect entire car wiring. Courtesy Ford Motor Co.

So the resourceful DIY hacker might think, why not go back to basics.
I did some further digging and came up with a selection of silicon sheathed wire (called flexible wire). This can be sized for 5A upwards choose your AWG. The advantage here is that the Si sheath is fireproof and decomposes at 600C. Copper melts at 1000C but rapidly looses strength before then. So a piece of Si wire say 2" long stretched with a modest spring should surely constitute a credible fusible link. The other concern is to contain the flash particles and potential ignition source, ( glass tube? fibre sleeving used in heaters). Its what I would do and you cant beat the physics. Just test the link and record results and you have taken proper duty of care. Thats enough heresy for today.

 

[Johan]

Another data point: I just dead-shorted a 150A MRBF fuse using 330Ah 48V LFP and 4/0AWG cable. Results are here.

 

[meetyg]

@MattiFin sadly you have shown that you are under-informed on the matter. DC systems have used blade switches since 1920+. You can see evidence of this in railway electric traction switchboards (600Vdc 1000A), Electroplating, early telephone exchanges, UPS etc.
However, and this is where your ignorance shows, Electrical power distribution and switch rooms requires operators to be specially trained, equipped full body flash suits, gloves, head googles when operating manual switch gear. There are YT vids to educate you.
On a more domestic note, the vid you showed, deliberately abused circuit breaking for clicks and drama. In reality you wear gloves to protect your hands from flash burns, wear googles to protect your eyes from UV and sparks. Its a moments operation in msecs to pull down a knife switch and the distance of separation immediately quenches the arc flash. For 12V there is no arc flash very minimal risk in auto systems. For 24V you can stick weld but the flash with quench easily within <5mm. 48 volt systems need much larger distances (I estimate 8x ) so proposition is that 50mm is a safe guideline - which I hope to demonstrate in a vid when I get all apparatus together.

Note - dc stick welding is generally ca 20V at work piece (once the arc is struck and in the CC region but starts at ca 60V to strike the arc) and 100-200 A dc. So gloves and face protection is essential but its no great drama.

Ill informed amateurs dont realise a 48V panel system pushes out full current on a sunny day and improper specified breakers may fail to cut the load in a roof fire for example (see vids of mcbs failing including a very popular one in OZ until recently banned

Here is a Vid showing positive support for hypothesis that a large knife switch will work well.

Notice the system is 48v (4 panels) in full sunlight. The arc flash is produced and sustained BUT when the distance is ca 2" it quenches. BTW you can blow the flame out or remove its heat (needed to maintain ionisation temp of ca 6000c by a simple plant mister filled with water.)

I propose also that an immediate arc fire remedy in ELV systems can use a simple plant mist bottle (as well as cable cutters)

I think the problem with the first video is incorrect wiring (he mentioned it also).

DC breakers should have arc chutes in them, but in polarized (polarity sensitive) these are only on one side, including magnets to pull the arc into the chute.
When you run them the wrong way, the arc isn't pulled into the chute and combusts the breaker into flames (the arc has nowhere to go).
Take a look at this DC breaker teardown:

That's also why you shouldn't use a polarized DC breaker between an inverter/charger (AIO) and your batteries, because current can flow in both directions.

But for PV panels, I don't think it should be a problem, if the breakers are properly rated and are from a good brand (unfortunately lots of fakes out there).