In Bussmann fuse, you will find there are some same current, same rated voltage, similar size fuse for selection.

For example, This 170M7802 and 170M6496

Similiarity: 

1, 800A, 1250VAC/DC high speed fuse, With same fuse ratings;

2, Both suqare Body semiconductor fuse;

3, Time-Current Curve;

How to make decision?

1, Base on your mechanical design

As you can see, 170M7802, Body size: 105*105MM; But 170M6496, Fuse body Size is much smaller: 76*76MM;

These are recently hot in Energy Storage Device circuit, if you have enough space, you can select 170M7802;

2, Base on Electrical Design: T-C Curve etc

Even these 2 fuses are with similar TC curve, The bigger size, the T-C curve is better in the same fuse ratings;

3, Ambient environment

For this big current environment, the working temperature is normally in 40~85C,or even higher, If you donot have cooling device( Cooling fan, Water cooling etc) inside device. The bigger fuse size, the better for cooling; 

Note: Fuse working temperature is -40~60C. The higher temperature, If you want the fuse work properly in this operation current, the fuse with need to change to higher current(According to the fuse ambient temperature derating diagram). Which the cost will be more.

4, Base on Cost

Bigger size, the cost will be higher;

5, Base on leadtime

Some parts which is popular in user, Bussmann Power will keep some stock;

But basically the part leadtime will be around 8 weeks for 170M series fuse.