While most of smarts in the ATS are in the electronics, the really nasty failures come from the mechanical part.

At the end of the day a high energy ATS looks just like a switch behind a meter in your house. There's a lip that goes from one position to another, except in a high energy ATS the lip is big and when the transfer occurs it slams from one source to another.

There are only so many of those physical slams that it can withstand to being with so you want to minimize that number.

The second failure mode is that after transfer to non-main source, the lip can get stuck there, making it impossible to switch back on the main. [Once I have seem the lip melt into the secondary position. While I thought it was weird, the guys from the power company said it is not that uncommon.] This creates a massive problem as the non-main source is typically not designed for long term 24x7 operation. So now you are stuck on a secondary feeding system and you cant just transfer to main without de-energizing the system i.e. taking the power out of the entire data center.