I am looking for all the meanings of "shall not". Is it closer to "must not" or "might not"?
In this example:
The circuit-breaker shall not trip.
does this mean must not happen or might not happen?
So archetypal uses are statements like, "This shall not stand." The meaning is very much "must."
Shall is used for both expressing a strong assertion or intention, and expressing an instruction or command.
In the last sentence, you can replace "shall not" with "must not."
In the context of instructions relating to a circuit breaker, 'shall not' implies there is a very important set of rules you, the reader, are responsible for.
If, in fact, the breaker -did- trip, you would be guilty of violating those rules.
It is possible that the use of 'shall' is intended to instill almost religious importance to these rules.
You do not give the entire context, however, or possibly the instructions are not thorough. Because, of course, the entire point of a circuit breaker is that it -can- and -must- trip, under fault conditions.
Likely, the statement is part of the instructions for testing the circuit breaker, and the implication is 'if the breaker trips, something is very wrong (perhaps the breaker is defective), and must be fixed right away.