I opened a heat pump cover and saw this little cable screwed onto the case but it appears to still be insulated from case and is supposed to be used by an electrician. Is this meant to ground the metal case of the machine?

enter image description here

Since there is no other external pin on the case, is this internal wire meant to be in contact with the case itself and in case of a malfunction that would put case under current, it would provide the current a path to the ground by going (I assume) to the same place the power supply cable ground cable connects to internally?

Or could it potentially be connected to the case on the other side (not visible on image) and is expected from electrician to pull this cable out through the case and connect it to some external grounding wiring? Or could it also be used just for bonding with other conductive items in the area?

I understand this requires professional. I am just curious to know if this is a rough explanation of what it does. The instruction manual provides no explanation and both seller and manufacturer failed to provide any response so far.

  • 1
    \$\begingroup\$ If that wire was intended as a grounding conductor, it should have green or green and yellow insulation. I'd make a wild guess that it is a temperature sensor of some sort. \$\endgroup\$ Jul 15, 2020 at 15:26
  • \$\begingroup\$ Thank you, I think you are right. I was researching a bit more and realized this cable is way too thin to be a grounding cable. \$\endgroup\$
    – miran80
    Jul 15, 2020 at 15:28
  • \$\begingroup\$ Almost looks like a thermistor but probably a dipped stripped wire end \$\endgroup\$ Jul 15, 2020 at 15:49
  • \$\begingroup\$ Agree it sure looks like a thermistor or maybe a thermocouple. \$\endgroup\$
    – Kyle B
    Jul 15, 2020 at 16:00
  • \$\begingroup\$ This can be something similar to honeywell 192 series thermistor \$\endgroup\$
    – Ravi
    Jul 15, 2020 at 16:43

3 Answers 3


If it has two wires on the end that plugs into a PCB, then it is a thermistor. Measure the resistance, and it should come in at a value that is 10KΩ's (could be more, but this is the usual value.) By the looks of it, it is there to measure the temperature of the air (as it isn't thermally connected to the case). A lot of thermistors I use look like this in my designs to measure ambient temperature.


There are high chances that this is a thermistor very similar to Honeywell 192-series discrete thermistor. These devices can have resistance varying from 1K Ohms to 100K Ohms.

I remember finding something similar and it was as discrete thermistor, which has uni curve with bare leads and epoxy on the top.

The one that I found was this honeywell 192 series thermistor (https://sensing.honeywell.com/sensors/thermistors/192-series)

How to Test

  • Measure the initial resistance
  • Bring the tip of the sensor close to the heating element and measure the resistance and compare to the initial measurement, the change observer must be high and must be sensitive to touch

No, the wire in that picture is not used for grounding.

That is a temperature sensor.

There are two wires coming into the sensor which has a protective coating, it looks like it is dipped to black epoxy resin. The sensor is mounted with the plastic part to the case with a screw, to place the sensor element to monitor temperature from the correct place inside the unit.

So leave temperature sensor where it originally was measuring the temperature.


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