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The low-down on standards for IR windows

12 December 2011

Establishing which standards and certifications are appropriate for your application of infrared (IR) windows can be quite a minefield but IRISS is here to help. In the latest chapter of its practical guide, it steers you through the myriad of design and safety regulations such as UL, ULC, IEEE, CSA and others.

What standards and certifications are relevant to infrared (IR) windows? This is one the most commonly asked questions when engineers and safety professionals begin to investigate IR windows. Trying to sort through the myriad of UL, cUL, IEEE, CSA and other standards can be a daunting task. This chapter will attempt to clarify some of the most pertinent standards.

The UL 50V classification for Infrared Viewports is the only standard that relates specifically to infrared windows. It serves more as a classification than an actual standard for performance-of-build characteristics. Specifically it states:
Infrared Viewports are a fixed aperture, consisting of one or more openings or a solid infrared transmitting media, surrounded by a mounting bezel or frame, that provide a means for the passage of infrared radiation.

The UL50V classification is actually a mix of two distinctly different product categories: the “infrared window” (also known as IR sightglasses or IR viewing panes) and the “infrared port”. While both will allow the thermographer to perform infrared inspections of targets located inside an enclosure or behind a barrier, they are mechanically very different.

Specifically, IR windows provide a barrier to separate the thermographer from the environment surrounding the target. In contrast, an IR port is essentially a hole. When opened, it effectively removes the barrier between the thermographer and the target. This distinction becomes important when considering the Personal Protective Equipment (PPE) implications of NFPA 70E/CSA Z462 (see Chapter 8).

UL508 covers industrial control equipment and control panels under 1500 volts. Equipment covered by these requirements is intended for use in an ambient temperature of 0-40°C (32-104°F) unless specifically indicated for use in other conditions.

UL 508A
UL508A covers industrial control panels intended for general use, with an operating voltage of 600 or less. This equipment is intended for installation in ordinary locations, in accordance with the National Electrical Code (ANSI/NFPA 70), where the ambient temperature does not exceed 40°C (104°F).

UL 746C
UL 746C sets the impact and flammability standards for polymeric materials used in electrical equipment up to 1500 volts. Any plastic or polymer forming part of an infrared window must pass flammability tests at room temperature, and must remain intact during an impact test performed at 0°C (32°F). It is worth noting that of the crystal optics capable of transmitting in the long wave portion of the infrared spectrum (8µm to 14µm), there are no fluoride-based crystals capable of passing the impact tests required in 746C. However, because they are classified as “glass” under the standard, they are not required to test for impact as long as they are thicker than 1.4 mm.
IEEEC 37.20.2 Section a.3.6
Viewing panes mounted in medium and high voltage equipment (600 volts to 38kv metal clad and
72kv station type gear) are required to withstand impact and load per IEEE C37.20.2 Section a.3.6. The standard specifically states that the viewing pane must withstand the impact and load from both sides (inside/outside) and the viewing pane must not “crack, shatter or dislodge.”

Unlike with UL, there is no exemption given to crystals or glass under the IEEE standard, and the only crystal capable of passing the test in this standard is sapphire (which is non-transmissive in the 8µm to 14µm (LW) portion of the spectrum where PdM cameras typically function).

Lloyd’s Register Type Approval
Lloyd’s Register provides independent, third-party approval certificates attesting to a product’s conformity with specific standards or specifications. It also verifies the manufacturer’s production quality systems through a combination of design reviews and type testing. There is growing international awareness of the importance of third-party certifications such as those offered by Lloyd’s.

Ingress Protection/Environmental Rating
IP65 is an international standard (defined in IEC 60529) that classifies products as “dust tight,” with complete protection against contact (with parts contained within the enclosure). It also covers resistance to directed water jets. IP testing must be performed and certified by third-party testing labs, such as SIRA.

11NEMA 4/4X and IP65 are equivalent ratings. It certifies enclosures for indoor or outdoor use; for protection against access to hazardous parts; for ingress of solid foreign objects (windblown dust); for resistance to water ingress resulting from rain, sleet, snow, splashing water, and hose directed water; and from damage due to ice formation. 4X also must resist corrosion. NEMA ratings can be self-certified when the manufacturer has sufficient data (such as third-party IP tests) to support the definitions.

Typically only viewports that are rated equal to or greater than that of the original enclosure should be used.

Arc Resistance
Per IEEE C37.20.7, arc resistance tests only apply to complete switchgear systems. Arc Resistant
Switchgear is tested with any number of accessories in place (with covers closed), and the system must contain, control and redirect the heated gases of the arc blast away from where personnel interface with the equipment. Because of the near-infinite variations in cabinet configuration, geometry and design, the results of one test cannot be assumed to hold true for another cabinet – particularly if that cabinet has no arc resistance features.

Components (such as IR windows) can never carry an arc rating because they have no innate arc resistance characteristics. The features that enable a switchgear system to protect personnel from the effects of an arc blast are a complex series of structural reinforcements, plenums and vent doors that redirect the blast. It is worth noting that all three major brands of IR windows have been a part of successful arc flash tests. However, this does not mean that any of these windows is “arc resistant” in its own right. As stated, it is the switchgear that has been shown to be arc resistant with the components in place.

Additional Resources
For more information on the standards cited in this chapter, please refer to the following white papers and web sites:
? For additional information about standards and how they relate to infrared window design, see “Safer by Design,” at
? For additional information about arc resistance standards, see “The Myth of Arc Resistant Windows,” at
? For additional information about UL 50V, see:
? For additional information about UL 508, see:
? For additional information about UL 508A, see:
? For additional information about UL 746C, see:
? For additional information about IEEE C37.20.2 section a.3.6, see:
? For additional information about Lloyd’s Type Approval, see:
? For additional information about Ingress Protection, see:
? For additional information about NEMA ratings see:
? For more information on IEEE C37.20.7, see:
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