Protection devices: A magnetic (electromagnetic) circuit breaker trips and opens the circuit to protect equipment under which electrical condition?

Introduction / Context:
Magnetic circuit breakers and overload relays protect wiring and equipment from damage due to excessive current. Knowing the parameter that causes tripping helps technicians select the correct protective device and diagnose nuisance trips versus genuine faults.

Given Data / Assumptions:

• A magnetic (electromagnetic) breaker uses a solenoid or magnetic actuator.
• Trip action is determined by the magnitude of current.
• Thermal or electronic elements may supplement magnetic action, but the trigger remains overcurrent.

Concept / Approach:
Magnetic trip elements respond nearly instantaneously to high overcurrent (short-circuit) conditions because magnetic force is proportional to current. Thermal elements respond to overloads over time using bimetal heating. In either case, the triggering quantity is current, not voltage, and certainly not a normal open or proper operation condition.

Step-by-Step Solution:
Fault causes current to exceed breaker rating (e.g., short to ground).Magnetic field in trip solenoid increases rapidly with current.Actuator trips the mechanism and opens contacts.Circuit is interrupted, protecting downstream equipment and conductors.

Verification / Alternative check:
Breaker curves (time–current characteristics) show trip times primarily as a function of current magnitude, confirming the overcurrent basis.

Why Other Options Are Wrong:
Voltage exceeded: overvoltage protection is typically provided by surge protectors or MOVs, not magnetic breakers.An open in equipment: an open reduces current, not increases it.Operating properly: no protective device should trip in normal conditions.

Common Pitfalls:
Confusing voltage surges with overcurrent events. While surges can cause high currents, the breaker trips on the current, not directly on the voltage magnitude.

Final Answer:
current is exceeded