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I'm looking into temperature switches and came across this type which warns against shorts and instructs you to use a provided plastic sleeve to prevent this. Although I'm linking to a specific product here please consider it just as an example of this type (of which there seem to be many out there).

It is described as:

"60°C Normally Open Thermostat Temperature Control Switch ... 250V 5A N.O Thermal Protector Metal Bimetal Temperature Controller"

Here's the warning:

enter image description here

It also separately says "Attention: Do not remove the plastic shell when using, and beware of electric leakage."

(source)

I'd like to understand exactly what could short to what. I wouldn't have thought that the outer metal shell would be conductive to the leads, but is that actually what this warning is about? If not, what are they warning against?

I suppose one lead might have continuity with the shell... but if that is the case why would they use conductive packaging at all? (Cheapness?)

Aside from the risk of a short causing a problem, I would ideally want the metal case to be directly on the object whose temperature is being measured for the fastest response without any insulating effect of the plastic.

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  • \$\begingroup\$ "Hezd" is probably a typo for "Head" \$\endgroup\$
    – Jasen
    Sep 12 at 9:31
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According to KSD9700 datasheet, one of the wires may be connected to the metal case. Anyway, the case is metal, so you would have to be careful that it does not short anything out in a circuit if it becomes loose. The warning is just so that you are aware of the different possible shorting abilities it has.

One of the reasons to use metal is that a rather good thermal conductor so the case temperature is coupled to the bimetal actuator.

The device is available in plastic case too, but plastic is more an insulator than conductor for heat.

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