The officially supported way to create a USB OS X Installer, for OS X Mavericks and later, is to use
createinstallmedia from within the downloaded installer application bundle.
Have a look at: Create a bootable installer for OS X
The following is from the link above:
Use the 'createinstallmedia' command in Terminal
- Download the OS X installer from the Mac App Store. Quit the installer if it opens automatically after downloading. The installer
will be in your Applications folder.
- Mount your USB flash drive or other volume. You could also use a secondary internal partition.
- Open the Terminal app, which is in the Utilities folder of your Applications folder.
- Use the createinstallmedia command in Terminal to create the bootable installer. Examples of this command are in the next section.
For detailed usage instructions, make sure that the appropriate
Install OS X app is in your Applications folder, then enter one of the
following paths in Terminal:
Path for El Capitan:
/Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia
This is the basic syntax of the command. Replace
the path to your USB flash drive or other volume, and replace
installerpath with the path to the Install OS X app.
createinstallmedia --volume volumepath --applicationpath installerpath
The following examples assume that the OS X installer is in your
Applications folder and the name of your USB flash drive or other
volume is MyVolume:
Example for El Capitan:
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
Note: You can substitute
El\ Capitan in the above command examples.