12. When do I need an electrically isolated probe?

To prevent an uncontrolled ground path, electrically isolated probes should be used in insulated bearings, where bearings may be electrically “hot”.

Motors and generators may have insulated bearings to prevent electrostatic discharge and dissipate through a controlled path such as an earth brush.  In this condition, a grounded probe may cause damage to the instrumentation as well as damage to the bearings.  

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