The Class 1E definition is found in IEEE 308. It is associated with electrical power systems found in nuclear power plants.
The U.S. Nuclear Regulatory Commission makes a special distinction between those systems, structures, and components (SSCs) that are important to safety, and those which aren’t. Safety-related SSCs have three defining characteristics. Similarly, the NRC makes a distinction between electric equipment that is important to safety, and that which isn’t.
CLASS 1E DEFINITION
Safety-related electric equipment is defined in 10CFR50.49 as equipment relied upon to remain functional during and following design basis events to ensure:
- The integrity of the reactor coolant pressure boundary;
- The capability to shut down the reactor and maintain it in a safe shutdown condition; or
- The capability to prevent or mitigate the consequences of accidents that could release radiation to the public.
The IEEE created its own term for “safety-related electric equipment,” which is “Class 1E.” In IEEE 308 it gives the definition of Class 1E as follows:
The safety classification of the electric equipment and systems that are essential to emergency reactor shutdown, containment isolation, reactor core cooling, and containment and reactor heat removal or that are otherwise essential in preventing significant release of radioactive material to the environment.
As you can see, the Class 1E definition supplied by the IEEE is much more specific than the definition given by the NRC. It names nuclear-specific systems and functions. The NRC acknowledges the definition in 10CFR50.49.
Class 1E systems and equipment are considered auxiliary systems because they provide power to the systems directly responsible for safety, such as engineered support features and the reactor trip system. In other words, the Class 1E power systems provide support functions to other safety systems.
Finally, there’s a crucial distinction between Class 1E equipment, and Class-1E qualified equipment. You can read more about that distinction by clicking here.