21920-5

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21920-5 application field and working principle

21920-5 is a category of electrical standards for motor control and protective devices in hazardous locations. It includes requirements for Class I locations (where explosive gases, vapors, or dusts may be present), Class II locations (where combustible dusts may be present), and Class III locations (where easily ignitable fibers and flyings are present). As such, 21920-5 covers the majority of industrial environments.

The working principle behind the 21920-5 standard is to ensure the safety of any personnel working in hazardous locations. All motor control and protective devices must be approved by an agency, such as UL, to ensure they meet requirements for maximum safety. For instance, any motors used in a hazardous environment must be approved to operate safely in that environment and must have particular safety features, such as explosion-proof housings, in order to protect personnel.

Additionally, any wiring used in these environments must also meet special requirements. Wires used in hazardous areas must be approved for their installation in such an environment and must be rated to handle the temperature and current that will be present. Also, any junction boxes used must also be approved for their location and installation.

When it comes to motor control, 21920-5 outlines that any devices used must be rated to operate efficiently and safely, while also providing the required levels of protection. Any motor starters used must be approved for the application and must meet certain requirements, such as allowing the motor to start and stop safely, overload protection, and more.

21920-5 also establishes requirements for other protection systems, such as fuses, circuit breakers, and grounding systems. For instance, all fuses must be of the proper operating rating and have an arc resistant design. Furthermore, circuit breakers must also be rated to handle the appropriate amount of current, while also providing the necessary protection.

Finally, grounding systems must also be in place in order to ensure the safety of any personnel working in the environment. All grounding systems must be properly configured to provide protection from ground faults and any exposed metal must be isolated to prevent electric shock.

In conclusion, the 21920-5 standard establishes a comprehensive set of requirements for motor control and protective devices in hazardous locations. In order to achieve maximum safety, all motor control and protective devices must be approved by an agency and comply with certain requirements. Additionally, wiring, junction boxes, and other protection systems must also meet certain requirements. By following these requirements, personnel can ensure maximum safety when working in hazardous environments.

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