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What is the UL698A Standard?

Updated: May 15, 2023

What is UL698A?


UL698A is a safety standard for industrial control panels (ICPs) specifically related to applications in hazardous locations. The standard is published by Underwriters Laboratories (UL), a global safety certification organization that creates many of the most important regulatory standards for the electrical, engineering, and construction industries.


UL698A builds on the UL508A regarding the design and building of industrial control panels, specifically adding specifications for ICPs classified as being located in hazardous locations under the National Electric Code (NEC), NFPA 70. In addition, the standard outlines specific ICP construction requirements for hazardous locations, such as fieldbus intrinsically safe concept (FISCO) applications, barriers, separation, and intrinsically safe apparatus.


As UL698A is essentially an addendum to UL508A for specific applications, all UL698A panels must be UL508A compliant, though it’s important to note that wherever there are conflicting requirements between the two standards, UL698A supersedes UL508A. In this blog, we’ll look at the important terms and specifications of UL698A and how you can ensure compliance with the standard.



Where Does UL698A Apply: Classes, Groups, and Divisions


Industrial control panels will require UL698A certification for all spaces regarded as hazardous locations under NEC NFPA 70 Articles 500 through 503. These can be broken down into several sections as follows:


Classes

  • Class I: This refers to locations that contain flammable gas, vapor, or liquid.

  • Class II: This refers to locations that contain combustible dust.

  • Class III: This refers to locations containing easily ignitable fibers or flyings.


Groups

Class 1 (flammable gasses, vapors and liquids)

  • Group A: Acetylene

  • Group B: Hydrogen, butadiene, ethylene oxide, propylene oxide, and acrolein

  • Group C: Ethylene, cyclopropane, and ethyl ether

  • Group D: Acetone, ammonia, benzene, butane, ethanol, gasoline, hexane, methane, methanol, methane, naphtha, natural gas, propane, and toluene


Class II (combustible dust)

  • Group E: Combustible metal dust, e.g., aluminum, lithium, titanium commercial alloys, and magnesium

  • Group F: Combustible carbonaceous dust, e.g., carbon black, charcoal, coal, and coke dust

  • Group G: Other types of combustible dust, e.g., chemicals, flour, grain, starch, plastic, and wood

These hazardous locations may be further classified into Divisions I and II.


  • Division I: This is where ignitable concentrations of any of the above hazardous materials exist under normal operating conditions. It also includes locations where the above hazardous materials can be caused or introduced by other actions, such as frequent maintenance, repair, or equipment failure.

  • Division II: This is where ignitable concentrations of the hazardous materials above only exist under abnormal operating conditions.

It is also possible for a location to be “unclassified,” which applies to areas where Electrical Area Classification is not required, as any presence of hazardous materials is very infrequent.


Understanding UL698A: NRBX & NNNY


Within the UL698A standard itself, there is an important distinction between NRBX certification and NNNY. The primary differences between these are:


NRBX: Designation for UL698A ICPs which feed into and govern hazardous environments but are not located in hazardous environments. This means, for example, that they require intrinsically safe apparatus such as control circuits but do not require explosion-proof, dust-ignition-proof, or pressurized enclosures.


NNNY: This is a more stringent standard for ICPs that are located in hazardous areas. A UL698A NNNY certification is required for environments with a Class 1 rating, signifying the presence of flammable gas, liquid, or vapor. This means the ICP must be NEMA Type 7 panels that are capable of containing any possible explosions of circuitry, sparks, or flares within the panel. They must also be non-incendive, i.e., incapable of starting or catching fire, which requires specialty components.



How to Comply with UL698A


Several steps must be taken during the designing and building ICPs for hazardous locations to achieve compliance with whichever “authority having jurisdiction” (AHJ) is signing off on your ICPS. Here are some of the most important elements for achieving compliance with UL698A.


Separation

Separation can be achieved in UL698A control panels by maintaining a specific distance between circuits, using partitions, or combining the two. To separate intrinsically safe circuits and non-intrinsically safe circuits by distance, including wiring and terminal, the spacing should be a minimum of 50mm (2”). Between different intrinsically safe circuits, it should be a minimum of 6mm (¼”) and with an insulation thickness of 0.25mm (0.01”). The separation distance between the ground and dead metal parts should be a minimum of 3mm (1/8”).


Partitions

Partitions should be 0.45mm (0.0177”) thick when made of metallic material and 0.9mm (0.0354”) when made of non-metallic material, though they will be thinner if they pass the mechanical tests outlined in Part 11 of the UL698A.


Maximum Surface Temperatures

The Classes (I, II, III) refer to flammable, combustible, and ignitable material, the difference between which is the temperature at which a fire is likely to start. In the design phase for UL698A panels, this will determine the calculated maximum surface temperature for the control panel. To comply with the UL698A, the maximum surface temperature must be in line with the guidelines for the specific material in the hazardous location.


Markings

Inside each UL698A panel enclosure should be the marking “WARNING” followed by “Explosion Hazard – Substitution of Components May Impair Intrinsic Safety” or “Intrinsically Safe Field Wiring Terminals.” Externally, any intrinsically safe field wiring outputs should be labeled “Intrinsically Safe Circuits.” In addition, the panel should also have the marking “Provides intrinsically safe circuit extensions for use in Hazardous Locations when connected per Panel Control Drawing No. _____” and the word “WARNING” followed by: “Explosion Hazard. To prevent ignition of flammable or combustible atmospheres, disconnect power before servicing”.


Conclusion


UL698A gives specifications for industrial control panels that are either located in or feed into hazardous locations. Control panel safety in these areas is critical for preventing harm to human health, such as around flammable gasses, vapors, and liquids. Therefore, the certification is very stringent on its specifications.


When designing UL698A control panels for hazardous locations, it’s vital to draw up compliant plans and ensure that the control panel and contingent components are also compliant. At Enercon Engineering, we’ve helped thousands of customers get exactly the control panels they need. We have one of the country's largest design and engineering spaces for ICPs and can help you achieve UL698A compliance for your applications. Read about our custom ICP solution creation or talk to our team to learn more.

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