Fuses and breakers--please help

[LarryEW]

Putting together my first system and have a few queries before placing the final order. I have 5-EG4 LL batteries (48V) wired into an EG4 bank and will be adding Victron components consisting of MP-II 48/5000 (2 units) + Lynx distributor + MPPT + smart shunt.

1- What mega-fuse sizes for the Lynx? Should they be 300 amp like the T-class I'll add to the (+) cable from the battery bank?

2- Circuit breakers between Lynx and inverters...I see many use 125 amp (seems low) is that correct for my system? Nader or a better DC rated brand?

3- I'm planning 4/0 between bank and Lynx then 2/0 to inverters. Should the latter cable be larger?

Thank you for any guidance!

 

[SeaGal]

IMHO, wiring should be sized to suit the load +25% overhead, as well as minimise voltage drop/rise. The latter will depend on length of cable.

Fuses should be sized to protect the chosen wire.

Here is a good guide which covers many of those aspects:-

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

 

[timselectric]

Victron?
Please hold, while I transfer you to @sunshine_eggo

 

[LarryEW]

Wire runs are rather short at 6 feet for the 4/0 and 3 feet for the 2/0. My thinking is that 2 units running split phase would max out at 10000/240 = 41 amps. Also the manual states that max input for each unit is 95 amps--so a 125 amp breaker on each 2/0 would cover those 3 ft cables.

I'm planning 125 amp fuses in the Lynx as well. We'll start slowly with solar input (1.6 kW) since we're surrounded by trees and increase if it works well. This setup is mainly for a longer term grid-down situation--just received a chargeverter yesterday and that'll be our primary input source at first. What am I missing?

Edit: I calculated the T-class based on 10000/.96/48 x 1.25 = 271 Maybe fuses along the 2/0 instead of breakers?

 

[ricardocello]

Victron recommends 200A fuses for DC to those inverters, and either 2/0 or 4/0 cable depending on length.
I would use 4/0 from the batteries and 2/0 to the multiplus-2s.
see section 4.2 in the manual

4. Installation

www.victronenergy.com

I use 300A class-t for 4/0 cable. some here would use thicker cable.
I don’t think you need more DC current than that for 2x5kva.

If you plan to use powerassist, the output ac current can be much greater than the input current

 

[LarryEW]

Victron recommends 200A fuses for DC to those inverters, and either 2/0 or 4/0 cable depending on length.
I would use 4/0 from the batteries and 2/0 to the multiplus-2s.
see section 4.2 in the manual

4. Installation

www.victronenergy.com

I use 300A class-t for 4/0 cable. some here would use thicker cable.
I don’t think you need more DC current than that for 2x5kva.

If you plan to use powerassist, the output ac current can be much greater than the input current

Appreciate the great info..do you also have a T-class fuse along your 2/0 cable? Or a circuit breaker?

 

[ricardocello]

Appreciate the great info..do you also have a T-class fuse along your 2/0 cable? Or a circuit breaker?

I have an EG4 rack with three EG4-LL v1 batteries (each has its own 125A breaker), combined onto busbars the rack, with
a 300A class-t fuse mounted inside the rack cabinet at the positive busbar.

From the battery rack, 10’ of 4/0 red and black class k welding cable goes over to my equipment rack along with a green 2/0 ground cable.

In the equipment rack, i’ve used a 600A victron busbar (not Lynx) which accommodates MEGA fuses.
For the two inverters, I run about 3 feet of 2/0 red and black class k welding cable to 200A MEGA fuses on the busbar.

Also on the busbar is a 125A MEGA fuse for the MPPT SmartSolar 250/100
and a 100A MEGA fuse for the 250/70 MPPT.

I also have a 125A fuse for the Chargeverter DC power.

All MEGA fuses are 58V or 70V rated, this is important (the 32V ones could arc at higher voltages).

 

[LarryEW]

I have an EG4 rack with three EG4-LL v1 batteries (each has its own 125A breaker), combined onto busbars the rack, with
a 300A class-t fuse mounted inside the rack cabinet at the positive busbar.

From the battery rack, 10’ of 4/0 red and black class k welding cable goes over to my equipment rack along with a green 2/0 ground cable.

In the equipment rack, i’ve used a 600A victron busbar (not Lynx) which accommodates MEGA fuses.
For the two inverters, I run about 3 feet of 2/0 red and black class k welding cable to 200A MEGA fuses on the busbar.

Also on the busbar is a 125A MEGA fuse for the MPPT SmartSolar 250/100
and a 100A MEGA fuse for the 250/70 MPPT.

I also have a 125A fuse for the Chargeverter DC power.

All MEGA fuses are 58V or 70V rated, this is important (the 32V ones could arc at higher voltages).

Many thanks for sharing your setup, all very helpful. Nice the 200 amp MEGA fuse covers the 2/0 with no circuit breaker required. Ready to finalize my order, cheers!

 

[ricardocello]

Many thanks for sharing your setup

No problem, it has been running for over a year without issues so far.

There are probably better ways to do it.
For example, I didn't even know what Lynx was, I would have gone that route if I had known.
The blue bug hadn't hit me yet.

Those fuses should never blow unless something dies in the inverters, and I'm not expecting that.

 

[ricardocello]

Nice the 200 amp MEGA fuse covers the 2/0 with no circuit breaker required.

I only use breakers where I expect to need a disconnect as well as over-current protection. DC breakers are expensive.

The Victron manual explicitly says fuses, so that's what I used. Best not to argue with the blue guys.