Electronic switch NO/NC Contacts???????

Depending on the type of switch it can vary. NC and NO are usually refered to as the idle state. No power, No activation. This depends on the duty assigned to the unit and what is controlling it. If the temperature switch is to control say hydraulic oil in equipment, you may have two switches. One will possibly turn a heater on to warm up the oil and make it flow better. This is probably the type you are refering to. It will close until operating temperature has been attained. Another may be used to turn off the pump (NC contacts) if the temp rises too high. This can also have a secondary contact to illuminate a warning light for Over temp shutdown. If a PLC is used it can just monitor the intput off the switch and either set off bells and whistles for the high temp shutoff, or display a PLEASE WAIT while oil is heated to operating temperature.

It all comes down to " are there any other components controlling or associated with the relay and what are they designed to do?". Does the switch provide "Cooling" or "Heating"?

NO/NC is always based upon "shelf" state although shelf is relative. In the case of a temperature switch that could vary depending on the activation parameters and if the unit is stored in the freezer or the oven. Seriously though, the problem is point of reference. Shelf state or process state. It maybe that once installed and in use then "Normal" will be if the temperature is above 150 degrees but on the storage room shelf the "Normal" condition is the opposite. For temperature switches, and pressure switches for that matter, the factor of the device range must be used. As an example, a temperature switch has both a high setpoint contact and a low setpoint contact. These close when the respective setpoint has been exceeded. The operating range is 100 degrees C to 500 degrees C then sitting on the shelf the temperature will be below the low setpoint and therefore the low setpoint contact will be activated or (closed if a NO contact). However, factoring in the range and the fact that it is a "Low Setpoint" then the contact will be referenced in the manufacturer's literature as Normally Open. Please note that the term exceed as used here means going beyond the limit or boundary set not "increasing above". This becomes more obvious (at least for me) when working with vacuum where a "higher vacuum" is actually a lower pressure.

NO means It is a "open-Contact" of a relay [Or a Switch] if not forced to change otherwise

NC means It is a "Close-Contact" of a relay [Or a Switch] if not forced to change otherwise

Com is the "Common-Contact" NO & NC [if a change-over ] or to NO or NC if not change-over

It is for a single SPCO [Single-Pole-Change-over] switch or set of contacts of a relay.

In Circuit diagrams all the contacts are marked with relay or Switch ref + contact number:e.g:NC1-sw1 which means SW1 is a multi-switch & this contact is part of the 1st set of contacts & is Normally- closed with its Com contact.

The rest of 2 contacts will be Com1-sw-1 & NO1-sw1.

SPST, SPDT, DPST & DPDT are single-pole single-throw, double-pole ....