I'am a question,

We use Cpanel/Webhost Manager to host websites on our server.

How i can find which files is cause a excessive usage of the bandwidth on a account?

Thanks

When you log into the domain's Control Panel and go to the Site Statistics. Click on the Webalizer link. There you should see something like "Top 10 URLs by KBytes". I believe that will list the files that used the most bandwidth.