A grounded junction is electrically connected to the sheath. An ungrounded junction is isolated from it. That distinction changes the questions to ask about the measurement chain: how quickly must the point respond, can the sensor sheath meet another grounded part of the installation, and could electrical noise affect the receiving instrument? The junction should be considered with the thermocouple type, sheath, cable, process point and instrument input. The physical location of the junction also matters when the sensor is mounted against a surface or inside a process assembly.
The catalogue shows both options on several records. Thermocouple MI lists J and K types with grounded and ungrounded junction choices. The Jubilee-clip surface thermocouple also lists J and K with grounded and ungrounded junctions, while its cable options include Tef/Tef and Fg/Fg/SS. The pipe temperature thermocouple lists K, J, T and RTD choices and grounded or ungrounded (isolated) junctions. These are catalogue options, not a universal specification for every assembly. Check each record for its own sheath, dimensions and cable details.
Selection is a measurement-point decision. A surface or pipe probe may need a mounting arrangement that keeps the junction in the intended contact position. A process probe may need its junction, sheath, cable and connection reviewed as one assembly. Ask whether the receiving input is configured for the selected type, how the installation is grounded, and where the cable runs relative to other electrical equipment. Also identify whether the point is accessible for inspection or replacement. Record nearby drives, switching equipment or other possible sources of interference.
When comparing the two junction styles, do not use response alone as the deciding factor. Electrical isolation, grounding arrangement, cable construction and instrument compatibility may be equally important. Provide the thermocouple type, sheath requirement, point location, mounting method, cable route and instrument input with an enquiry. A selected catalogue record can then be checked for the junction choices and dimensions it actually lists. Include the intended purpose of the reading and any existing connector or wiring detail so the comparison addresses the complete measurement chain. A replacement enquiry should also identify the current junction and cable arrangement.