Title: IEC TR 60890: A method of temperature-rise verification by extrapolation for low-voltage switchgear and controlgear assemblies 1. Introduction IEC TR 60890 is a Technical Report (not a full International Standard) that provides an alternative, simplified method for determining the temperature rise inside an empty or partially filled enclosure (e.g., a low-voltage switchgear and controlgear assembly – LV switchboard). It is used when full-scale testing is impractical or too costly.