This is an excerpt from a recent educational article by Banner:

In safety standards, the term “category” is commonly used to specify a particular level of reliability. ISO 13849, which deals with the safety of machinery and its control systems, defines “category” as the classification of the safety-related parts of a control system based on their ability to resist faults and their behavior when faults occur. In essence, a category explains how a safety circuit is wired, how it detects faults, and how it responds to them. There are five categories: B, 1, 2, 3, and 4. These represent a range from least to most reliable in maintaining safety in case of a fault.

In practice, Banner Engineering’s SI-GL42 Series of locking safety interlock switches, like all mechanical interlock switches, can typically meet Category 2, Category 3, or Category 4 depending on the number of switches used per gate, whether the switches are wired individually or connected in series to the safety control system, and other requirements. Selecting the proper category for your safety function designs requires conducting a risk assessment to identify the hazards and risks that will need to be addressed.

To read the complete article, click on this link:
https://www.bannerengineering.com/us/en/company/banner-blog/selecting-the-right-interlock-switch-safety-category-level.html

Sincerely,

Julius Frago,
The Automation School