The term “Class 1E” explained

This is a critical term that electrical engineers must know. It’s closely linked to the term “safety-related”. But there’s a critical distinction that many engineers overlook, especially if they are inexperienced . . . .

The term “Class 1E” is a special term that describes safety-related electrical equipment. It is redundant to call electrical equipment both Class 1E and safety-related. Emergency diesel generators are Class 1E equipment. So is the instrumentation that monitors critical plant parameters like neutron flux in the core and radiation levels inside containment.

It must also be noted that equipment is classified “Class 1E” based on its function, not on its qualifications. To be classified as Class 1E, electrical equipment must perform some safety-related function. Yes, it must be qualified to survive seismic events or harsh environments, but a qualified breaker that is sitting on a shelf is not a Class 1E breaker because it is not, at that time, performing any safety-related design function. Once it is installed inside of an MCC or panel for the purpose of performing electrical isolation between Class 1E power and non-Class 1E power, then it will become a Class-1E component.


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