In the design, material selection, production, and sales process of wires and cables, there are many temperature parameters such as 90 ℃, 105 ℃, 125 ℃, 150 ℃, etc. These parameters are commonly referred to as temperature resistance level parameters in the industry. So, how did these parameters come about? Why do materials with a temperature resistance level of 90 ℃ have different aging temperatures? What is the relationship between aging temperature and temperature resistance level? What is the definition of the maximum long-term operating temperature allowed for conductors with insulation? What is temperature index? What is the rated temperature of the material? Can silane crosslinking material meet the temperature resistance level of 125 ℃?
1, UL standard
In UL standards, the common temperature resistance levels are 60 ℃, 70 ℃, 80 ℃, 90 ℃, 105 ℃, 125 ℃, and 150 ℃. How did these temperature resistance levels come about? Is it the long-term operating temperature of the conductor? In fact, these so-called temperature resistance levels are referred to as rated temperature in UL standards. It is not the long-term operating temperature of the conductor.
Rated operating temperature
The confirmation of rated temperature in UL standards is determined according to formula 1.1 (see Chapter 4.3 Long term Aging of Materials in UL 2556-2007). The specific process is to first assume a temperature resistance level of the material, such as 105 ℃, and then calculate the test temperature of the oven at 112 ℃ according to formula 1.1. The samples are placed at these test temperatures for 90 days, 120 days, and 150 days, respectively, to obtain the data of the elongation change rate and aging days of the samples. Then, the linear relationship between the aging days and the elongation at break is calculated through the least squares method. Based on this linear relationship, the elongation at break of the samples aged for 300 days at this oven temperature (112 ℃) is calculated.
Short term aging temperature
The short-term aging temperature of the material, which is the most common 7 days, 10 days, etc. in the standard, such as 105 ℃ material, the aging condition is 136 ℃ x 7 days. What is the relationship between this and the rated temperature? In UL standards, the temperature for short-term aging is obtained based on the long-term usage experience of the material, but some methods have also been summarized to confirm it. Determine the short-term aging temperature of a material as described in Chapter 4.3.5.6 and Appendix D of UL2556-2007 standard.
2, EN/IEC standards
In EN/IEC standards, it is rare to see the rated temperature as in UL standards. Instead, the conductor's long-term operating temperature or temperature index is used. So what is the difference between these two temperatures?
In the EN/IEC standard system, the evaluation of the temperature resistance level of cables is mainly based on EN 60216 or IEC 60216. This standard mainly evaluates the thermal life of insulation materials. The evaluation method is to conduct aging tests on the material at different temperatures, with a change rate of 50% in elongation at break as the endpoint of aging, to obtain the number of aging days of the material at different temperatures. Then, through linear regression, the aging days and aging temperature are linearly correlated to obtain a linear relationship curve. Then determine the maximum operating temperature based on the lifespan of the cable, or determine the lifespan of the cable based on long-term operating temperature.
3, National and industry standards
In the process of formulating national and industry standards in our country, many contents are based on and borrowed from UL standards or EN/IEC standards. For example, in GB/T 32129-2015, JB/T 10436-2004, and JB/T 10491.1-2004, both materials and wires have temperature resistance levels of 90 ℃, 105 ℃, 125 ℃, and 150 ℃, which is clearly a reference to UL's standard system. The term 'heat-resistant' refers to the maximum allowable long-term operating temperature of a conductor. The expression of heat resistance clearly refers to the IEC standard system.
