"server rack fusing”

Question:
Because the T-Fuses are acting fast (which is required here), but how fast is fast? In a server rack filled with 6 EG4 batteries with 100A max. continuous output current it would require a 600A T-fuse at the first look. But what about surge load peaks? I don't know how realistic it is that a surge will pull more than the 600A if a huge inductive load starts. The EG4 batteries can handle surge amps of >102A for 30s and >150A for 3s. The internal short circuit protection in the BMS will trip at >300A per battery in <0.1ms according to documentation.

How should the T-fuse be correctly sized?

Is an additional T-fuse in the rack really necessary or does it make sense if there is a separate 200A battery breaker between the main busbar and each inverter (on top of that, each battery has a it's own 100A mechanical breaker and the BMS as a last resort)?

fmeili1 said:

In a server rack filled with 6 EG4 batteries with 100A max. continuous output current it would require a 600A T-fuse at the first look. But what about surge load peaks?

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Fuses protect wires. Don't worry about how many batteries, and continuouse output.
What is the max current for your inverter? Size the wire for this, then pick the correct fuse to protect the wire.

I suggest the Class T fuses for protection against "catastrophic events" like you drop a bare metal rachet and it lands across the pos & neg creating a dead short and releasing 20,000 + Amps.
I also suggest for day to day work on your system and isolation, a 2P molded case circuit breaker (MCCB) between the ESS and Inverter. This should be non-polarized and DC rated.

In my own system:
Each of my DIY batteries internally (at the suggestion of one of the forum members) has a Mega-fuse between cells #8 and #9 (16s pack)
Each DIY pack externally has a 125A 2P DC breaker.
From each pos pack terminal and the rack, I install a 1P 125A DC breaker, the neg terminal connects with 1AWG to the neg bus bar -800A copper
After the 1P breaker on the pos side, a 1AWG cable goes to one side of a 125A class-T fuse, the other side bolts directly to the pos bus 800A bar.

Each Main bus feeds with 4/0 to a 2P MCCB to allow shutting down the whole ESS with one switch. (required where I live).
After the Main 2P MCCB I put the shunt on the neg and the pos connects to a 400A Class T fuse.
After the shunt and 400A Class T the pos and neg each terminate on a four stud bus (one for pos one for neg)
Each of the three inverters then simply connect to the four-stud bus. Keep the wire lengths for the inverter pos all the same length, and the neg side all the same length.
With this system, all the packs are protected, any/all the packs can be isolated/removed while the main system runs and the lights stay on. An interal short with a pack would trigger the Megafuse and cutting the circuit and reduce each half of the pack to 24volt DC. So far I have never blown any fuse, nor tripped any breaker. I have run the 400A Class T pretty close to it's max rated current, it has never tripped. I have ordered a 500A in preparation for an expansion of the system to 24kW output.

OffGridForGood said:

EG4 Chargeverter - for AC charging. Available from Signature solar and Current Connected. Highly rated by users on the forum here, I don't have one yet, but going to get one.

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Just ordered the Chargeverter from Signature Solar, not expected until March , maybe!!

threepets said:

Just ordered the Chargeverter from Signature Solar, not expected until March , maybe!!

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A decision that you will never regret.
Best money spent for my system.