As with most electronics, it is good to avoid making connections while circuits are energized. Therefore, we recommend that your Arduino be unpowered and disconnected from USB when plugging or unplugging the shield from it. The same goes for the socketed Wixel. After all of the connections between the Wixel, shield, and Arduino are secure, the Arduino can safely be powered through the power jack or USB. It is safe to connect the socketed Wixel to your computer through USB, but the Arduino will not receive power through that connection.