I have a question I'm looking at a IRF1404Z MOSFET and it says it has a max Continuous Drain Current of 190A it's on a power drill so under normal operation it would never get that high but could if you try and operate the drill with a locked motor?

I ask because I did a cross reference with a STP200NF04 but it's only 120A

 

190A - it's a theoretical number impossible to achieve in real life.
Also notice that at 75A the legs on the MOSFET would melt (Package Limited).
Also do you understand that this 75A is given at case temperature equal to 25°C? Do you understand what this means?

 

I would assume that it changes over the case temperature?

 

Try read this
http://homepages.which.net/~paul.hills/SpeedControl/MosfetBody.html#2.2
http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.html

 

Thanks, good read.