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ASTTBC RFPT — Fire Alarm Systems (AL) · Question

Calculate the minimum battery capacity (including 20% safety factor) for a voice system with 0.5 A standby current and 2.0 A alarm current for 30 minutes of alarm.

U = (I_standby * 24) + (I_alarm * (T_alarm/60)). Multiply by 1.2 for the 20% safety factor (aging). For a voice system, T_alarm is 30 mins (0.5 hours). (0.5A *

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Question: Calculate the minimum battery capacity (including 20% safety factor) for a voice system with 0.5 A standby current and 2.0 A alarm current for 30 minutes of alarm.

Answer options:

  • 12.5 Ah
  • 13.0 Ah ✅ 15.6 Ah
  • 20.0 Ah

Correct answer: 15.6 Ah

Explanation: U = (I_standby * 24) + (I_alarm * (T_alarm/60)). Multiply by 1.2 for the 20% safety factor (aging). For a voice system, T_alarm is 30 mins (0.5 hours). (0.5A * 24) + (2.0A * 0.5) = 12 + 1 = 13 Ah. 13 * 1.2 = 15.6 Ah. 17 Ah is the next standard size.

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