Shunt trip breaker sizing?

[NorthTown2022]

I am going to be installing an off grid 48v Quatro 5000. It is a 4000 watt inverter. It has a peek wattage of 10000v. I have calculated I could potentially draw up to 208 amps. Is this the only factor I should keep in mind when purchasing shunt trip breaker? Is a 250amp breaker sized appropriately? Is it safe to use one that can handle even more amperage?

How about the PV voltage and amperage?

 

[Bud Martin]

May I ask why you want to use 'Shunt trip breaker' type?

 

[Rednecktek]

May I ask why you want to use 'Shunt trip breaker' type?

Aren't those on AC breakers?

The peak wattage aren't really a big issue, do your math via the max standard load (4kw), so 4000/48 = 83a * 85% efficiency = 95.8a * 20% overhead = 115a, which probably don't exist so you can go with a 120a just fine.

 

[NorthTown2022]

May I ask why you want to use 'Shunt trip breaker' type?

I am considering a Batrium BMS, it would be used to isolate the battery in case of a failure.

The peak wattage aren't really a big issue, do your math via the max standard load (4kw), so 4000/48 = 83a * 85% efficiency = 95.8a * 20% overhead = 115a, which probably don't exist so you can go with a 120a just fine.

Thank you! Any idea if a 250 or a 400amp would be ok as well?

 

[rmaddy]

Any idea if a 250 or a 400amp would be ok as well?

It's there to protect the wire. You can use a larger breaker but only if the wire is big enough to handle it. For a 250A you must be using 1AWG or larger. For a 400A you must be using 4/0AWG or larger.

But take a look in the Quatro manual. It should tell you the recommended fuse size.

 

[chrisski]

With breakers, you need to consider the AIC rating also. The two big inverters I purchased recommended a class T fuse. I’d recommend a breaker with an AIC rating bigger than a Class T fuse if your inverter manual manual asks for a class T fuse. When I looked for these large AIC DC breakers on MIdnite solar, they were not available in a variety of sizes. Class T fuses were.

A proper AIC rating will prevent an arc going across the tripped breaker, which would complete the circuit anyway. Lithium batteries have such a. Huge potential to limit current on the forum usually class T fuses are recommended.

Another thing to consider is the breaker able to take the wire? I have only used breakers up to 6 awg. I have seen some of the large breakers come with studs for lugs. Not breakers, but I have bought busbars rated for 250 amps that I could not fit a 4/0 lug on. I have also got a couple other pieces of equipment that I could not fit the wire size in I wanted. The worst was the one that said up to 8 awg wire, but only 10 AWG fit.

Breakers also take up a bit of space, especially if you put it in a case, which is probably required. The class T fuses are big 6”, and the breakers in a box are bigger.

I have not went with breakers for large wattage loads for these reasons.

 

[NorthTown2022]

Think I have a better understanding now. Thank you!