Re: Number of wires connected to a Breaker
Looking at the terminal may give you a clue as to if the terminal is listed to be used with more than one conductor. If the terminal screw itself doesn't directly secure the conductor it most likely tightens a saddle of some type which the wire is placed under. As such the screw is in the center in conductors may be able to be place on each side, i.e. a SqD QO breaker.
It is also a good indicator that only one conductor is allowed if there is a simple whole for the wire and a scew or to clamp it down. However, don't take it for granted. As previously posted examine the device itself for a label or instructions that would indicated that it is in fact allowed or not.