Is it safe to use the same power source for Arduino and its Motor shield? Is it safe to use a unique 12V 5A DC power source to feed both Arduino and its connected Motor shield, provided that


the motor (connected to the shield) will eat 3A maximum
the Arduino Vin will get the power


Arduino and the shield exchange information, and use both the same power supply, is there some risk of "interference" of some kind?

edit

This is the motor controller shield I intend to use. In the manual, the connections show that 


the Arduino and the shield have different power supplies
the Arduino power pins are not used by the shield
In my case, when I was running my DC motors at full load, I noticed a large voltage drop in the circuit. This could affect the signals or transmission of data on the Arduino.

It is definitely recommended to power the arduino and motor shield with separate power source. Make sure the the share a common GND.