What is a transfer switch and where is it used in LV power systems?

• A. A device that converts AC to DC
• B. A device that selects between two power sources for critical loads
• C. A device that steps down voltage
• D. A device that isolates circuits for maintenance

Answer: (C)

A transfer switch is a device that selects between two power sources for critical loads, allowing seamless switching from one source (like the main utility) to a backup source (such as a generator) when needed. In low-voltage power systems, this is essential to keep essential equipment running during outages or disturbances, either automatically or manually. The switch ensures the loads aren’t fed from both sources simultaneously and avoids back-feeding. This concept is different from converting AC to DC (that’s what a rectifier does), from stepping down voltage (that’s a transformer), or from simply isolating circuits for maintenance (that’s an isolation or maintenance switch).