[codefox1]

Always remember that even test equipment with transformer power supplies usually have a capacitor and sometimes resistor from line to ground. I've rewired my AC operated stuff to 3 prong plugs used with a known correct power strip. Now then, a set you are working on may not have this mod yet, but if it is also transformer operated and powered by an isolation transformer, the chassis can almost certainly be linked to the mains ground through a resistor, or directly. Anyway the object is to not get little jolts or worse whilst connecting and using test equipment or creating other problems as already mentioned.