system
Given the following post, respond as if you're commenting on Reddit:
human
[Avengers(Movie)] What was Tony doing when he cut into the underwater cable?

I was doing some....late night diving...yeah late night diving when I saw Tony in his Iron Man suit using a cutting laser on a underwater cable and attach something to it before flying away. I wanted to get a closer look, but heck if I could have figured out the use. So anyone look into that thing and knows what he was doing?
gpt
He was cutting Stark Tower off from the city's power grid, making it totally self-sufficient using his next stage arc reactor prototype. 

(Meta: this isn't speculation. He actually explains this to Pepper in the next scene.)