We are sorry any time we hear of devices getting damaged. However, even in cases where a cascade of failures can be traced back to a failure of one of our products, we limit our liability to the initial value of our product. It is my understanding that our refusal to consider paying for this customer’s other damaged property is what he is characterizing as “refusal to accept any sort of responsibility”.
Whether USB isolation is “proper” is a design consideration for the user, and we believe there are many applications where the cost exceeds the benefit. We certainly do not advertise or imply any isolation in the Tic T500, and it is unrealistic to expect USB isolation in a $20 motor controller. (By the way, we do not have that even in our $150 motor controllers.)
With the Tic T500 in particular, we think there is reasonable circuitry between the motor supply and the USB 5V line. We use quality, name-brand components in our products, and we believe it is unlikely that the Tic is the root cause of the incident in question. We are happy to troubleshoot what might have led to the system failure.