When there are multiple electronics sub-system interconnected, I have seen some applications where one of the sub-systems will include a current limiting resistor as well as some EMC related components at its ground input to protect itself. The case being that this device is on a vehicle, and when another device on the vehicle lost its ground, it began to use the ground connection of the first device and caused damage to the device (before it had a ground protection designed into it). Now, if 2 boxes are talking to each other on some kind of digital interface, it is necessary for them to share a common ground reference. However, it is possible if one device malfunctions and has a bad ground, it could cause the other device to malfunction as well, right? Is it better to protect against the potential ground fault issue, or to ensure both boxes always have a solid common ground?