IEEE 303-1991

IEEE 303-1991 is a recommended practice for auxiliary devices used with motors in Class I, Groups A, B, C, and D, Division 2 locations. It addresses the application of motor-related accessories and control components where flammable gases or vapors may be present under abnormal conditions, helping engineers select and arrange equipment with appropriate attention to safety and reliability. For power, energy, and industrial applications, this standard supports more consistent design decisions in hazardous-area motor installations.

IEEE 303-1991 overview

This standard focuses on the auxiliary devices associated with motors installed in Division 2 hazardous locations, where electrical equipment must be considered in relation to the surrounding atmosphere. IEEE 303-1991 is useful for understanding how these devices should be applied so that motor systems remain practical, dependable, and suitable for the intended environment. It provides a technical reference for engineering review, equipment selection, and coordination of auxiliary components in installations serving industrial power systems.

Typical use cases

IEEE 303-1991 is commonly relevant when specifying or reviewing motor-mounted or motor-adjacent auxiliary devices such as sensors, switches, terminals, and related control accessories in hazardous-area settings. It may be used for facilities handling combustible gases, refinery and processing equipment, or other industrial locations classified as Class I, Groups A, B, C, and D, Division 2. The standard helps support equipment planning for motors that must operate with added controls or monitoring devices.

Why this standard matters

Using IEEE 303-1991 can help reduce uncertainty when evaluating auxiliary devices for hazardous-location motor applications. It supports more consistent procurement, installation review, and engineering documentation by giving a shared reference for the intended operating context. That can improve compliance efforts, limit compatibility issues, and help teams make better-informed decisions about performance and safety. In practice, it is a useful document for controlling risk where motor systems and classified atmospheres intersect.

• Motor auxiliary devices for hazardous locations
• Class I, Groups A, B, C, and D
• Division 2 application context
• Industrial power and energy systems
• Design, selection, and compliance support