The changes in power supply classification from 2^nd edition to 3^rd edition dealt with definition, not performance. Both the 2^nd and 3^rd revisions required two mechanisms for guarding each in the event of a failure. For the area of basic electrical safety and avoiding shock hazard, the 3^rd edition further divided means of protection into operator protection and patient protection. These classifications in the 3^rd edition required medical device manufacturers to define the classification in terms of “Means of Operator Protection” (MOOP) and “Means of Patient Protection” (MOPP) as determined by an ISO-14971 Risk Analysis/Management process. The table here summarizes these classifications and the type of power supply solution that would be appropriate, depending on whether one or two levels of protection were required. Edition 3.1 then implemented a number of changes to address issues identified as unclear in the 3^rd edition. These changes covered subjects such as essential performance, risk management, mechanical testing, temperature testing, and humidity, as well as new specifications for mechanical and electrical hazards.