Re: Dry Form C Contact
I wonder if I have missed out on something here, as this discussion differs from my (admittedly limited) experience.
I have never seen the notation of "a, b, and c contacts" used in connection with manual switches. For switches that are part of a process sensor, such as a pressure switch, or level switch, or temperature switch, I usually see the contacts described in terms like "closes on high temperature" or "opens on low pressure," and not as "a, b, or c contacts."
My experience with the "a, b, c contact" notation has been limited to relays. In that world, an "a contact" is open if the relay is de-energized, and a "b contact" is closed if the relay is de-energized. The only relay I have ever used that had "c contacts" was one built by the manufacturer to be capable of being used as an "a" or a "b," but that required the installer to physically unscrew, flip, and re-tighten the screw, in order to change it from an "a" to a "b." In other words, that particular relay did not have an SPDT contact, but rather a "wire it as you wish" contact.