Essential Performance (EP) initially came into the IEC 60601 series of standards when the 3rd edition of IEC 60601-1:2005 was published. The definition was quite confusing and many manufacturers, regulators and test houses had a hard time with it and how to apply it properly. In 3rd edition (2005) + amendment 1 (2012) some clarification came into play which made it easier to understand but there is still a fair amount of confusion.
Interpretation Sheet on Essential Performance & Single Fault Condition for IEC 60601-1:2005+A1:2012
