To install Windows 10 on a second SSD or HDD, you will have to: While you can, I would suggest that you not remove the external SSD or Hard Drive unless it is necessary. When you install Windows, the Bootloader will register the path of the installed OS. If it is missing, then it can be problematic. Also do not remove the OS from primary SSD or HD, especially if you plan to remove the second SSD and plan to use on a need per basis. Connect the secondary SSD or the hard drive to your computer....

Read the full article at The Windows Club