The NC designation, when applied to switch types and usage, indicates a set of contacts that is Normally Closed, or the terminal that is part of the normally closed circuit through the switch. When used in schematic drawings and component pinouts, NC is also used to indicate Not Connected or No Connection. The NC designation is often written as N/C.
Positive Break is a switch technology term indicating that the internal operating mechanism of the switch is via a rigid or non-resilient member, which is designed to ensure that the switch contacts will in fact open when the switch is actuated. This is in direct opposition to the typical design of a snap-action actuator as found in many microswitches, which is generally a spring-operated mechanism.