The new 20kW Multiplus manual states an 800A fuse between the battery and inverter. I’m struggling to find any combined fuse switch that big. Does anybody have any suggestions that don’t cost an absolute fortune.
Thanks
You don’t want a fuse/ switch that’s less reliable then ess system itself.
Yes those from aliexpress are cheap, but is it worth?
Would a NH3 fuse disconnect link be suitable?
Thanks for the reply
I was really looking to use some kind of 800A rated fuse switch disconnect but I can only find NH3 disconnect modules rated to 630A.
I don’t have a massive amount of space either so separate fuses and switches would be a bit of a problem.
Thanks
Use the 630A one.
You’ll almost never exceed that amperage.
20kW / 50V is about 400A at maximum.
Thanks for the reply
I presume they over spec to allow for surge currents but 800A seems massively overkill. Annoying that they spec something like that but don’t sell a solution.
I think the 630A is looking like my best option.
Thanks
2x 120 mm2
Means 2x 400a fuses.
And depending on how fast blow they are size does matter.
Do you have regs requirements that need both negative and positive fused? If not then only fuse positive.
Don’t skimp here 20kVA is alot of big bad things going wrong.
If cost is an issue wait untill you can do it right.
Or aim smaller on the inverter.
They already exist?
In normal running no. But in a fault condition very possible and if some users are to be considered (the ones who overload often) then yes needed. Again rate of blow matters
I suppose that you are not suggesting paralleling fuses, even if they are on different (parallel) wires… (NEC Section 240.8)
I suppose i should have added the usual disclaimer
**Local regulations apply…
That’s no “local regulation” stuff… It’s the physics we all learned in school.
You can’t have a perfect balance according with Kirchhoff’s first law on two parallel 400A fuses for a total of 800A…
So it may be 425+375.
Slowly the 425 will heat up and will finally blow.
Then the whole 800A will be on the “shoulders” of the remaining fuse which will see the double of its capacity and will effectively explode.
In my book, never ever parallel two fuses for doubling the amperage.
800A is the fuse for the peak power (just a few seconds) and short circuit.
As you wrote yourself the max continues current will be around 400A.
And I will re iterate, that local regulations apply. A juristictional statement does not mean everyone must comply
Not all of us use NEC.
Jurisdiction aside though Kirchoff’s law cannot be ignored.
I guess then on the bigger ones i am going to be considering using both fusing individual cables and using the big single disconnect. To me now having one conductor that could be in trouble but not enough to trip the single big disconnect is now a different thing and dangerous in itself.
The fuse should be also determined by
1.) The battery bank’s shortning current
2.) Cable size.
3.) System voltage
So we need more info to give a safe anwser.
For such a big system a combined fuse/switch would be too expensive, think very heavy industrial grade load-interruptors.
Instead go for a seperate Battery switch and Fuse.
Jean Müller KETO Series for TelCo 80V/750A size NH00.
KETO-00-1/F/750A/250V
T507111302
That would be perfectly ok. The fuse trips at the rated amps, and rhe fuse can also be removed with an isolated fuse gripper.
To remove the fuse under high amp load might give some sparks, but that situation is very unlikely to occur and not dangerous.
You can easily remove the fuse from its holder and use it as an isolation switch.
With a bit of creativity you can even attach an (insulated) wire to it to a remote lever, to be able to open the circuit from a distance,
That’s how i have arranged it in the engine room of our boat.
That looks perfect. Thank you!
To add some information maybe for future systems:
NH fuses dont stop at NH3, there is also NH4/NH4a going up to 1600A.
There are 3 pole disconnects for NH4a which could easily take 800A NH fuses