2 Overview of IEC 60730 and UL 1998 Classifications

To create a foundation for fault control techniques, both the IEC 60730 and UL 1998 specifications divide products into classes. The class assignment is determined by a hazard and risk analysis applied to the specific control. This analysis is based on both the likelihood of the failure and the resulting consequence of the failure.

IEC 60730 defines 3 classes: A, B and C:

• Class A: controls are not related to safety
• Class B: controls intended to prevent unsafe operation
• Class C: controls intended to prevent dangerous hazards

UL 1998 defines two classes: 1 and 2. UL 1998 class 1 is comparable to IEC 60730 class B and UL 1998 class 2 is comparable to IEC 60730 class C. For class definitions and examples, see Table 2-1.

The standards define the components that must be tested along with examples of acceptable measures to detect faults/errors of that component. Depending on the class, the components to test include the CPU, clocks, volatile and non-volatile memory, internal data path, I/O and communication interfaces (Table 2-2). In general, for each component there are a few types of measures that the developer can choose from to verify/test component functionality. These suggested measures can be:

• Hardware-based
• Software-based
• A combination of both hardware- and software-based

The implementation of IEC 60730 acceptable measures are meant to detect, and prevent, unsafe conditions and hazards associated with the equipment. These requirements are derived from the IEC 61508 standard "Functional safety of electrical/electronic/programmable electronic (E/E/PE) systems." The focus of IEC 61508 is how to apply, design, and maintain automatic protection systems called safety-related systems.