HomeMy WebLinkAbout407.011 - Fire Alarm System Voltage Drop and Battery CalculationsEffective Date: October 2013 Justin H. Beal, Fire Prevention Engineer
Current Revision Date: 7/28/2023 Section 407.011
Next Revision (3) Date: 7/28/2026 Page 1 of 2
Fresno City Fire Department
400 Fire Prevention Manual
SECTION 407.011 FIRE ALARM VOLTAGE DROP AND BATTERY
CALCULATIONS
PURPOSE
The purpose of this policy is to clarify the Fresno Fire Department’s (FFD or
Department) requirements related to fire alarm system voltage drop and battery
calculations.
APPLICATION
This policy applies to all fire alarm system plans within the City of Fresno and contract
service areas. These requirements apply to both required and voluntary systems.
OPERATIONAL POLICY
Based upon the need for uniformity in application across the Department’s diverse
service delivery area, and after careful deliberation, the Department has determined
the following:
1. The starting voltage for all voltage drop calculations is required to be
20.4 volts, or a reduction of 15% of fire alarm system voltage, whichever
is greater.
OPERATIONAL GUIDELINE
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PROCESS
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Effective Date: October 2013 Justin H. Beal, Fire Prevention Engineer
Current Revision Date: 7/28/2023 Section 407.011
Next Revision (3) Date: 7/28/2026 Page 2 of 2
INFORMATION
As noted in the currently adopted version of the California Fire Code (CFC), the fire
code official has the authority to formulate policies they deem necessary based upon
local conditions related to fire alarm installations.
Additionally, the CFC requires fire alarm shop drawings to be submitted to the
authority having jurisdiction (AHJ) for review and approval. One of the required
elements of these drawings is voltage drop calculations.
Standard engineering guidelines note that fire alarm system cabling size must
increase as the distance to the last device on the circuit increases.
Additionally, as batteries age, their performance also degrades, and these two factors
must be accounted for when completing voltage drop calculations.
DEFINITIONS
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CROSS-REFERENCES
California Fire Code (CFC), current edition