What is the function of a switch that has no interrupting rating and is operated after a circuit has been opened?

The primary function of a switch that has no interrupting rating and is operated after a circuit has been opened is to isolate a circuit. This means that the switch is intended to provide a means of separating a part of a circuit for maintenance, safety, or troubleshooting purposes. Since it has no interrupting rating, it cannot be relied upon to safely interrupt a fault current while the circuit is live, emphasizing that it must only be operated when the circuit is already de-energized.

Isolating a circuit is crucial for ensuring that work can be performed safely without the risk of electrical shock or equipment damage. The switch will effectively create a physical separation from the power source, thereby removing the potential for electrical energy to flow in that portion of the circuit.

The other functions listed, while relevant in different contexts, do not apply to a switch with no interrupting rating operated after a circuit is opened. For instance, connecting power sources or managing load distribution implies the switch would have to operate under live conditions, which isn't feasible given the characteristics of the switch in question. As for operating signaling equipment, that's not the primary role of an isolation switch and does not relate to the safety aspects associated with circuit isolation.