You can register an unlimited number of devices associated with a single TWC ID, however only three can connect simultaneously using the same TWC ID.
To register a device:
Note: Be sure to remove old devices when you no longer use them. Not removing these devices could affect your total usage report and savings calculations. It could also impact your ability to access TWC WiFi as only 3 users can sign in with your TWC ID simultaneously.
Registered devices will expire after a year. You can either renew the device (re-cache) or remove it from the Device Registration.