A technician is commissioned to install a new standby generator for a small commercial building with a 120/208 V, three-phase, 4-wire service. The transfer switch must be capable of automatically switching the entire load. Which type of transfer switch is most appropriate for maintaining continuous building operation during a utility outage?

Question: A technician is commissioned to install a new standby generator for a small commercial building with a 120/208 V, three-phase, 4-wire service. The transfer switch must be capable of automatically switching the entire load. Which type of transfer switch is most appropriate for maintaining continuous building operation during a utility outage?

Answer options:

• Manual transfer switch.
• Non-automatic open transition transfer switch.
• Bypass-isolation transfer switch. ✅ Automatic transfer switch (ATS) with a closed transition.

Correct answer: Automatic transfer switch (ATS) with a closed transition.

Explanation: For continuous operation without interruption (or minimal interruption) during a utility outage, an Automatic Transfer Switch (ATS) with a closed transition is ideal. A closed transition allows for momentary paralleling of utility and generator sources, preventing power interruptions. A manual switch requires human intervention, and an open transition switch creates a momentary power interruption during transfer. Bypass-isolation switches facilitate maintenance but don't inherently prevent power interruption during transfer.