Battery disconnects / isolators @ 400A

I’m looking for a 2-pole battery isolator that can handle 400A…

The battery already has an overload protection breaker built in, but that only opens the positive and I need to open negative as well to comply with the isolation requirement.

So ideally I want a disconnector (switch) and not fuses nor a breaker. Any ideas?

Give us some more background info as there might be a easier way with smaller cables and multiple disconnectors coupled together. Im saying this as 400A is huge and will also need some serious cables. Biggest I have seen is 200-250A keto disconnectors

So I’m planning to use a FreedomWon Lite 20/16 battery with 2x Multiplus II 48/5000. The battery ships with 2x 50mm leads per pole.

The Victron manual says to use 200A fuses each for that 9000W peak power. The battery can delivery 400A continuously.

So with that, I gather I need a switch capable of 400A, otherwise it will melt first. A 250A fused disconnector will work, but then that will go first during a peak or fault.

I’m still planning, so compromises are inevitable.

What your battery can deliver and what your inverters can draw are very different.
I see its a 52V battery and with two multis you wont draw more than 200A and actually when you get to 7-8000w it will start warning you anyway which is about 160A draw.

Also your two cables of 50mm2 is easier than having 1 cable of 95mm2, not sure of the brand or specs of the cable but it will easily handle the 200A

here is a table for welding cable for example, but please check specs of your cables.


1 Like

Yes, that makes sense. I’m viewing “what battery can deliver” as max, with fault current higher.

What lead me down this path is Victron’s 200A fuse in the manual. That’s obviously there so your 100A fuse doesn’t blow when you have peak current. And with two inverters, 200A x 2 = 400A.

Now this will almost never be reached. A 250A fused disconnector still gives a bit of headway above the standard 100A x 2, but not a lot, so peaking will blow it.

So yes, 400A is a bit much, but 250A seems too little. (This is a bit backwards, since you select fuses based on cables normally, but I’m selecting both based on inverter manual.)

@mariusm It just so happened that I have a brand new Mersen Multibloc 2P 250A with three 200A fuses still in the box. It was purchased for a project but never used.

If you are interested I will let it go for R1000.

Might take you up on that, but still in planning phase…

Sure, no problem. Just give me a shout.

Are you using a busbar to join power from battery or you cabling direct to inverters?
Be very careful if you cabling direct because you cant disconnect the negative unless you unplug the network cable between parallel multis, it will pop the coms card.

In my install I had fuses only on positive from inverter to busbar and then i had full disconnectors with fuses from the batteries to busbar. And if you worried about fault current those keto/mersen fuses have a huge fault rating

I would install 2 times No0 ketos. 1 for negative and one for positive. I would use 2 x 160 fuse links in each. One for each inverter.

And also remember, the fuses should be able to protect your cables. If there is a 400amp fuse between your battery bank and the inverters, the cables to the inverter should also be able to handle the 400amps

So my plan was actually to use a Lynx distributor busbar: it has space for 2x 200A mega fuses on the positive for each inverter, an MPPT, an then the battery input.

That neatly handles the per-inverter fuses while keeping the negatives intact in all cases. Each inverter gets its own cable set sized correctly. Battery cables to bus is sized correctly based on breaker inside battery.

But the regulatory requirement for disconnecting the battery entirely messes with that plan, hence the disconnector. And non-fused disconnectors don’t seem to exist in these sizes. It seems silly (and the ratings are silly high) to now talk about fusing everything again. Do the Ketos have non-fused link accessories that allows them to just be isolators?

@JacoDeJongh Not quite sure how you’re suggesting to wire the 160A fuses, won’t that break the negative and then the inverter?

@Whatyamacallit, you basically went the “fuse everything again” route?

Just curious… That Freedomwon battery has a magnetic disconnect built-in. There is no need for an additional fuse if you ask me.

The freedom one gets connected to neg and pos busbar. From the 35-50mm wire to two poles of each fuse folder. From the opposite side of the fuse holder 35-50mm wires to the inverters. That way you would have a 160 amp fuse on both the neg and pos of each inverter.

If the downstream cables are capable, then no. But that only disconnects the positive, and you should isolate both positive and negative according to regs (while keeping the Victron negatives connected).

If you use smaller cables, based on likely load, etc. then the battery breaker is too big, so you need additional smaller fuses. I’m trying to avoid this, but it might end up being a lot less expensive than finding a “simple” disconnect that is sized correctly based on the battery breaker.

The original thinking was that better cables will be less expensive than thinner cable + extra fuses, but now it seems that extra fuses are inevitable.

This is totally new to me… Please explain.

Marius, I am currently driving down to Capetown for 5 installations, I am trying to make a drawing of how we wire Victron’s according to the south African regulations, I am not sucsessfull …

Can I maybe give you a call I guess I would cover more ground quicker…

If it’s okay, please PM me your number.

1 Like

1 Like

We will talk after your install :laughing:. its better than your house burning down
I didn’t put more than necessary