How are automatic transfer switches for emergency systems described?

Automatic transfer switches (ATS) for emergency systems are described as electrically operated and mechanically held. This means that the operation of the switch is controlled by electrical signals, usually triggered by a power outage or fault condition. When the primary power source fails, the ATS automatically detects this and switches the load to a backup power source, such as a generator.

The term "mechanically held" refers to the physical mechanism that keeps the switch in its new position once it has been activated. This ensures that the switch remains in the correct position without requiring continuous electrical power to maintain that state. The combination of electrical operation and mechanical holding is crucial for ensuring reliability and safety in emergency power situations.

The other options do not accurately describe the functionality of these switches. For instance, manual operation would not provide the automatic response needed in an emergency, and being automatically held without a mechanical component could compromise the integrity or reliability of the switch's performance. Thus, being electrically operated and mechanically held is key to the effective functioning of automatic transfer switches in emergency scenarios.