Get to Know UL 1604

Jane N. Awittor

November 19, 2013

2 Min Read
Get to Know UL 1604

Engineers who specify electrical products for industrial equipment tend to have a good working knowledge of UL ratings. However, one rating that gives many engineers trouble is UL 1604, which certifies electrical components for use in hazardous environments. We routinely field questions about UL 1604 and which products comply with it. Here are the answers to some of those questions.

What Is UL 1604?
This rating applies to most types of electrical equipment, circuits, and components operating in conditions that the National Electrical Code (NEC) defines as hazardous due to the presence of flammable gases, combustible dust, or ignitable fibers. The NEC categorizes these conditions as Class I for gases, Class II for dust, and Class III for fibers or flyings. While referred to in North America as UL 1604, this standard has been supplanted by a global standard known as ANSI/ISA-12.12.01. The requirements are similar.

UL 1604 also addresses whether a flammable material is present as part of normal operating conditions or is present only during abnormal operations. The NEC refers to these two scenarios as Division 1 and Division 2, respectively.

Finally, UL 1604 considers different types of hazardous materials according to their NEC codes. Codes A, B, C, and D segment different gases and vapors according to their ignition temperatures. Codes E, F, and G segment dusts according to ignition temperatures and conductivity.

Putting all the classes, divisions, and codes together, here are UL 1604's key provisions:

  • Apply to equipment, circuits, and components designed specifically for use in hazardous locations the NEC classifies as Class I and II, Division 2, and Class III, Divisions 1 and 2.

  • Provide minimum requirements for the design, construction, and marking of electrical equipment for use in these locations.

  • Cover Class I, Division 2 equipment in which the circuits and components are incapable of causing ignition of a specified gas under normal operating conditions.

  • Cover equipment constricted to reduce or exclude the entrance of dust in Class II and Class III locations.

  • Apply under specific atmospheric conditions, including ambient temperature between 5C and 40C, oxygen concentration no greater than 21 percent, and nominal barometric pressure of 1 atmosphere.

  • Apply to portable battery-powered equipment, other than flashlights, in locations defined as Class I and II, Division 2 and Class III, Divisions 1 and 2.

UL 1604 has other provisions and excludes some electrical equipment covered by other standards. If you're in doubt about whether a specific component or piece of equipment is compliant, it's a good idea to contact your vendor's application engineering team.

Jane N. Awittor is a product engineer for Panasonic Electric Works Corporation of America.

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About the Author(s)

Jane N. Awittor

Jane N. Awittor is a product engineer for Panasonic Electric Works Corporation of America. She's an electrical engineer with five years of experience specializing in passive IR (PIR), IR arrays, and pressure sensors.

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