Alternating-current systems of less than 50 volts shall be grounded when supplied by transformers exceeding which voltage to ground?

When dealing with alternating current systems less than 50 volts, grounding is an important safety requirement to prevent electric shock hazards. The correct answer indicates that these systems must be grounded when supplied by transformers that have a secondary voltage exceeding 150 volts to ground.

This regulation is supported by safety codes and standards which emphasize the need to ground lower-voltage systems when interfacing with higher voltage systems to ensure that any fault conditions can route excess current safely to ground. If a transformer provides more than 150 volts to ground, it signifies a higher risk of potentially dangerous voltages entering the low-voltage system. Grounding these systems minimizes the risk of injury or equipment damage by providing a safe pathway for fault currents.

On the other hand, the other voltage thresholds do not meet the regulatory requirements or best practices for grounding when they are below 150 volts. Systems supplied by transformers operating at these lower voltages may not necessitate the same level of grounding as those at or above 150 volts, thereby maintaining safety while also considering practical aspects of installation and maintenance.