Disconnector Switch for 4000AH Batteries

400AH doesn't tell you what you need to know. That could be 400A for an hour or 40A for 10 hours. Look at the peak output current your system is going to produce or consume, fuse it for that and buy a disconnect switch rated for that level at least, a little more wouldn't hurt.

respected sir, i appreciate your help and apologize for not giving the full information.

We have the battery bank consists of batteries of 3000AH for 10 hr's, bank voltage is 48 V, bank has 4 strings in parallel, so total capacity is 12000 AH for 10 hr's. and we have 400 amps disconnector switch for each strings.

Now we are going to update the system with 4000AH for 10 hr's, volatge will be the same 48 v, now we will have 6 strings in parallel, total capacity of 24000 AH, and according to my judgement 600 amp disconnector for each string will be more then sufficient .

I just wanted to cross check and take the guidance from senior guys, which will benefit me.

Thanks

Why not have knife switch disconnector on individual strings and an MCCB against the lot per standard practice?

Knife switches would be OK so long as there away from the battery banks. Inadvertent operation of a switch near the batteries could be disastrous. There are Ex battery disconnects, but I can't remember who made them.

The disconnect switch rating should depend upon the anticipated load. If your updates have not changed the load, then the existing disconnect switch might be OK, if it was correctly sized originally. The battery bank can supply several thousand amps, but the load is likely to be much lower. Disconnects, wiring sizes, and fuses are sized according to the load.

http://www.heinemann-electric.com/t-cata.htm --- These Heinemann units may help. Some of these hydraulic magnetic circuit breakers can be used for some very high DC current loads. I have used these for 48 volt DC. Although they are built for AC some are also tested and rated as DC. Each unit weighs about a half kilogram or more and has robust wire size fittings. You will have to determine the efficacy for life cycles as applies to switching, from the individual data sheets.

A car battery can supply more than 1000A into a short circiut. 4000Ah can supply more than 90000A into a short circuit. Depending on inductance in the output connected, you may get an arc votage of hundreds of volts on a fault. Use DC rated fuses outside the battery room, as well as an arc suppressing "snap action" isolator.

Ensure good ventilation and extract, for the hydrogen and oxygen while the batteries are being charged.