Control principle: An electromechanical relay is an electrically operated switch (coil actuates contacts), not a manually operated device. Evaluate the statement that a relay is operated manually.

Introduction / Context:
Relays provide galvanic isolation and allow a low-power control signal to switch higher-power circuits. Understanding how relays are actuated is fundamental in control and protection systems.

Given Data / Assumptions:

• Electromechanical relays contain a coil, armature, spring, and contacts.
• Applying current to the coil generates a magnetic field that moves the armature.
• Manual switches exist, but they are not relays.

Concept / Approach:
By definition, an electromechanical relay is actuated by an electrical signal. While a technician may physically install or replace relays, their operation in-circuit is electrical, not manual. Latching relays add magnetic holding, but still rely on electrical actuation.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets specify coil voltage/current and contact ratings, underscoring electrical operation.

Why Other Options Are Wrong:

• Correct: Mischaracterizes relay actuation.
• Ambiguous / Cannot be determined: Standard definitions remove ambiguity.

Common Pitfalls:
Confusing manual test buttons on some relays with normal actuation method; those are maintenance features, not the principle of operation.

Final Answer:
Incorrect