I’m installing a Victron 48V Multiplus-II inverter/charger along with an EG4 48V 280Ah Wallmount battery. The Victron inverter manual recommends fusing the inverter’s battery connection with a 125A fuse. The EG4 Wallmount battery has a built-in 200A breaker in-line with its output. Is the 125A fuse really necessary in this case, or is the 200A breaker good enough? My cables are 2/0 and about 3 feet long. The installation will be a lot cleaner without the external fuse.
If the intent of the fuse is to protect the wire (which is normally the case),
Your 2/0 AWG wire is probably not rated for 200A continuous, but that’s ok.
On the other hand, in normal circumstances, you won’t have 200A continuous to the Multiplus anyway, it will be less than 100A for sure, so the 2/0 is more than adequate.
And the breaker should be 125% of the wire rating, so 2/0 is good.
If the intent is to protect from a catastrophic short in the multiplus, a 125A fuse makes sense. But the 200A breaker is still likely going to trip in that scenario.
For me, it comes down to your level of trust in the DC breaker (Nader?) built into the battery.
Personally, because I prefer safety, I would put the fuse in.
I trust those breakers as disconnects, but not to protect my house.
I Australia, each battery bank needs it own fuse and isolation. You then need a main isolation breaker and each inverter needs its own fuse. If you have one battery you can use a fuse or breaker on the battery and have a breaker for the inverter.
An elegant soloution is to put a mega fuse or ceramic ANL fuse just below the unit.
I will mention though, that the 2/0 cables supplied by EG4 are very flexible, with high density strands of copper, must be a thousand strands in there. I have no doubt they are rated for at least 200A. As you say though, in this case it doesn’t really matter.
I agree, that if the inverter had a catastrophic failure resulting in a battery terminal short AND the battery 200A breaker failed, something could burn in the inverter. Seems like a very unlikely situation to have both simultaneous failures, but for peace of mind I guess I should put a “fast-blow” 125A external fuse in-line with the positive battery cable. The Mega Fuse seems like a good, economical choice. Guess I’ll do that.
Sounds good. Let us know if you can find a reasonable inline MEGA fuse holder.
For reference, in my setup, I use a Class T fuse inside the 300 Ah battery rack, and each rack mount battery has its own 125A DC breaker. I then cable over to my + and - busbars on 4/0 AWG.
I use a Victron 600A busbar (not Lynx) with the blue MEGA fuse holders to fan out to inverters, MPPTs, chargers, etc. I recommend 58V, or better, 70V rated MEGA fuses.
Yes, after doing a bit of searching, it looks like it may have to be a Class-T block and fuse in order to handle the 2/0 cable and still have a cover fit over it. So much for “economical”
The ceramic ANL fuse is very good and cheap up 125V DC and 6000A. The circuit breaker on the battery will have short circuit protection and should be very fast.
