All Pearson Current Monitors which have the 3-1/2 inch or 10-3/4 inch diameter hole are double shielded. The outer shield (case) is automatically grounded when the threaded mounting holes are used with metal screws through a grounded bracket. All other standard Pearson Current Monitors are single shielded. The shield and the coaxial cable braid are grounded by the mounting screws in all models except those having a 2-inch diameter hole. These have insulated mounting brackets and the only grounding is through the cable braid to the oscilloscope.