Thermocouple Extensions Leads. A range of thermocouple extension leads in types K, J, T and N available with either a miniature or standard IEC connector. The thermocouple extension leads are available in 2 m, 5 m and 10 m lengths. Cable Construction:. PVC insulated cable IEC colour coded Laid flat, side by side & PVC sheathed Insulation rating -10 105 °C. Miniature connector (flat plug pins) or standard connector (solid, round plug pins) versions available Contacts are polarised to prevent incorrect connection