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Let’s take another look at both the Temperature Classes and the ‘Major” hazardous area classes (Classes I, II and III) so that you don’t confuse them.

Class I & II:
• Class I applies to vapors and gases.
• Class II applies to dust.
Nothing changes with these Classes…these provide ratings for areas, rooms and locations. But the Temperature Class Rating covers the light fixtures that could be used in these locations, as follows:

So – Why is a Temperature Class needed?

For Class I: The Temperature Classification for a light fixture can’t exceed the ignition temperature of the specific gas or vapor to be encountered in the material Groups listed.

For Class II: The Temperature Classification for a light fixture must be less than the ignition temperature of the specific dust to be encountered in the Dust Groups listed.
So - to prevent the BOOM! mentioned earlier from happening, lights rated for Hazardous Locations get tested to find out how hot they will get. Sensors are placed on a Light Fixture to measure the hottest outside part of the fixture. This temperature is then listed as a “T” rating on a temperature rating chart.
Temperature Classification: What’s this look like?
• Lighting fixtures are identified with a Temperature Class.
This is either identified by a ‘T’ rating or by a temperature in
degrees C.
•The Temperature Class identifies the hottest temperature
produced by the outside of the lighting fixture.
COMING NEXT:
Technical Journal #14 will provide "T-Rating" examples & "Typical Self Ignition Temperatures for Gases & Dusts".
Bill Nagengast, President and Lighting Engineer, Solas Ray Lighting, holds over 20 patents in the lighting industry.
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TJ-13 2.16.18