The materials covered by this program have, in many cases, been investigated with respect to retention of certain critical properties including dielectric, tensile and impact as part of a longtime thermal-aging program conducted in accordance with UL 746B, the Standard for Safety of Polymeric Materials -- Long Term Property Evaluations.
The end-of-life of a material at each test temperature in this program has been assumed to be the time when the value of the critical property had decreased to 50 percent of its original (as received) value. If a material has been investigated under the thermal-aging program, the relative temperature index (RTI), in degrees C, shown is based on a comparison with a material which has acceptable service experience and correlates numerically with the temperatures above in which the material is likely to degrade prematurely.
If a material has not been investigated under the thermal-aging program, the temperature index shown is based on the generic class of the material. A tabulation of the temperature indices according to the generic material class is included in UL 746B and is based on the past field-test performance and chemical structure.
More than one RTI may be appropriate for a given material depending on the property requirements for a specific application. In certain cases, higher temperatures are permitted if so specified by the end-use product Standard.
Relative temperature index (RTI)
Maximum service temperature for a material where a class of critical property will not be unacceptably compromised through chemical thermal degradation. This spans over the reasonable life of an electrical product, relative to a reference material having a confirmed, acceptable corresponding performance defined RTI.
The electrical RTI is associated with critical electrical insulating properties.
RTI mechanical impact
The mechanical impact RTI is associated with critical impact resistance, resilience and flexibility properties.
RTI mechanical strength
The mechanical strength (mechanical without impact) RTI is associated with critical mechanical strength where impact resistance, resilience and flexibility are not essential.