When WECO speaks of continuous temperature limits, it refers to the material and not the environment. The temperature of a terminal block is a combination of heat generated by the electrical current flowing through it and heat exchanged with its environment. The heat exchange (inwards and outwards) with the environment is a combination of conduction, convection & radiation. The environment is the atmosphere, the enclosure, the wires, the mounting surface, other components and so on. We can see that the temperature of the environment is complex and cannot easily be reduced into the temperature of the surrounding air. We are concerned with hot spots in the connector’s components (internal and external) and the material’s ability to withstand this safely. Continuous temperatures always refer to the temperature of the connector materials. In the case that an RTI temperature is given, this means that the dielectric polymeric resin material was tested to UL 746B Polymeric Materials Long Term Property Evaluations and its Relative Thermal Index (RTI). This test last 5000 hours and the mechanical & electrical properties must not deteriorate more than 50%. Both UL 1059 Terminal Block Standard & CSA 22.2 no. 158 Terminal Block Standard refer to RTI. UL 1059 & CSA 22.2 no. 158 apply to ambient temperatures of 40 C (104 F) or less, the tests were done at 15 to 35 C (59 to 95 F). Ambient temperatures above 40 C (104 F), in principle and in practice, would require material review, special marking, extra testing and derating.
