scope:

This recommendation concerns the classification of metallic resistance materials intended for heating purposes. To classify resistance wires on the basis of: - maximum working temperature; - resistivity at room temperature; - temperature dependence of resistivity. Since the resistivity is not a linear function of temperature over the whole temperature range from room temperature to maximum working temperature, the temperature dependence cannot be characterized by a single temperature coefficient. Therefore, the classification table includes the resistivity at 500 ° C and at maximum working temperature, besides the resistivity at room temperature.