Originally Posted by hardgear69
Can I use 2-2-2-4 mobile home feeder to wire a 100amp subpanel in my new garage 300 ft from my house
The short answer is NO!
#2 mobile home feeder is not rated for 100 Amps under the circumstances you have outlined. #2 Aluminum wire is only good for 90 Amps in this scenario. It's only approved for a 100 Amp service as the sole feed for a dwelling unit. Since a detached garage does not qualify as a dwelling unit, you are limited to 90 Amps.
You can still use a 100 Amp panel in the garage, but connect the #2 feeder cable to a 90 Amp breaker in your main house to be compliant ..... UNLESS ...
If you want to deal with voltage drop issues, then you will have to increase the wire size relative to your connected load. Once you increased the wire size, then you will be able to use a 100 Amp breaker at the house.
While there are many posts here that calculate voltage drop based on a full 100 Amp load, in real life that is rarely the case.
Have you performed a load calculation on the garage?