Ground-fault protection on receptacles and outlets operating at _____ volts must use a Class A GFCI.

Ground-fault protection is crucial for safety, especially in damp or wet locations often found in residential and commercial settings. A Class A Ground Fault Circuit Interrupter (GFCI) is designed to trip when it detects a ground fault as low as 4 to 6 milliamps, providing a high level of protection against electric shock.

According to the National Electrical Code (NEC), any receptacle or outlet operating at 150 volts or less that is used in areas where moisture is prevalent, such as bathrooms, kitchens, outdoor spaces, and near pools, must be protected by a Class A GFCI. This requirement helps ensure that any fault current is quickly detected and the power is cut off, reducing the risk of severe electrical shock or electrocution.

While the other options suggest lower or higher voltage levels, the NEC specifically mandates the Class A GFCI protection for voltages up to and including 150 volts. This is in line with safety standards aimed at preventing accidents and injuries associated with ground faults in electrical systems.