batteries - How "slow" is a Class T "slow blow" fuse?

I have a DC inverter that's rated for 3kw sustained with a 6kw peak (for up to 5 seconds).

Per the Inverter manual, the manufacturer recommends a battery fuse rated for "at least 350 amps".

How can I determine what size fuse would be ideal in order to accomplish the following:

1. Never blow at 3kw/250amps (inverter's nominal rating)


2. Allow surge currents of up to 6kw/500amps for up to a few seconds


3. Blow pretty darn quick after the 6kw/500amps threshold

I was considering a 400amp fuse, but I'm not sure how to determine if it fits the bill without trying. Frankly, I'd rather have a breaker with similar characteristics since these fuses are upwards of $50 a piece, but it is what it is.

This is a photo of the fuse: http://ecx.images-amazon.com/images/I/71FMkor8t7L.SX355.jpg

Answer

Firstly, don't buy critical components from Amazon or Ebay or any other general online retailer. When you need a component that has to meet specific requirements, you need a datasheet. And when you need a datasheet, you need to buy the component from a reputable distributor.

Here's a fuse that I found on Digikey that might be close to what you need: 0298400.ZXH (I didn't actually compare it against the requirements you mentioned, so don't assume it's the right one). The datasheet has these figures that you'll need to study to determine if it meets your requirements:

If this part fails your requirements, you can use the parametric search tool (which any good electronics distributor will have) to find more fuses and compare their datasheets.