The Oscilloscopes ground clip causes a short circuit when you attach the oscilloscopes probe ground clip to negative supply. The circuit board ground is sometimes tried to the safety earth but other times the circuit boards ground is floating isolated from earth. If I attach my oscilloscope probe ground clip to a floating circuit board ground reference it will use a short circuit. High Voltage Opto-Couplers cause this issue too when I attach my oscilloscopes probe ground clip on the floating ground reference, it will cause a short circuit because the oscilloscopes probe ground clip is tied to the safety earth. When is it ok to use the oscilloscopes ground clip and when is it not ok to use it?