Wiring between battery and power supply must not exceed what voltage drop percentage according to NBFAA?

• A. 5%
• B. 10%
• C. 15%
• D. 20%

Answer: (C)

The maximum voltage drop allowed between the backup battery and the power supply is fifteen percent. This limit ensures the power supply always receives enough input voltage to operate correctly and to recharge the battery even when the circuit is drawing current. If the drop exceeds this amount, the supply may see too little voltage, leading to improper charging or failure to operate during a power outage. In practice, you size the wiring (gauge and length) to keep the drop at or below 15% under worst‑case load, balancing reliability with cost. If you need to verify, measure the voltage at the power supply input with the battery connected and the system loading conditions at their worst, confirming the drop stays within the 15% limit.