If you have mounted another drive in WHM and are running out of space on the first drive, you can transfer accounts to the new drive / folder as outlined below.
Type "Rearrange an Account" in the search box on the left, select the account you would like to move to the new drive / folder, and click rearrange.
You will then be presented with the screen below which will automatically select your other home folder (home2). If the automatic selection is incorrect you can select the correct one from the dropdown.
Click on "Move Account" and the process will begin. Once complete for some strange reason Wordpress sites don't work after the transfer to the new directory. We then restarted the server and all worked as expected. I understand this is not ideal and would love to hear if anyone has any suggestions on how to solve this.