The power source for a power-limited fire alarm circuit must be a listed PLFA or Class ____ transformer.

The power source for a power-limited fire alarm circuit must be a listed PLFA or Class ____ transformer.

• A. 1
• B. 2
• C. All of these are acceptable
• D. 3

Answer: (D)

Power-limited fire alarm circuits are designed to be fed only from sources that constrain energy to safe levels. The NEC requires the power source for these circuits to be either a listed PLFA (power-limited fire alarm) supply or a Class 3 transformer. A listed PLFA supply is specifically evaluated for fire alarm use, ensuring the output stays within the required voltage and current limits under normal and fault conditions. If a PLFA isn’t used, a Class 3 transformer provides a controlled, energy-limited output that meets the safety and performance needs of fire alarm devices. Class 2 is not specified here, and while it is also energy-limited, the standard in this context calls for Class 3 or a listed PLFA.

Power-limited fire alarm circuits are designed to be fed only from sources that constrain energy to safe levels. The NEC requires the power source for these circuits to be either a listed PLFA (power-limited fire alarm) supply or a Class 3 transformer. A listed PLFA supply is specifically evaluated for fire alarm use, ensuring the output stays within the required voltage and current limits under normal and fault conditions. If a PLFA isn’t used, a Class 3 transformer provides a controlled, energy-limited output that meets the safety and performance needs of fire alarm devices. Class 2 is not specified here, and while it is also energy-limited, the standard in this context calls for Class 3 or a listed PLFA.