NFPA 731 Secondary Supply.

The secondary supply is permitted to be a storage battery dedicated to the premises security system arranged in accordance with 4.4.4.
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The secondary supply is permitted to be a storage battery dedicated to the premises security system arranged in accordance with 4.4.4.

In security systems that require two independent power supplies, consideration must be given to acceptable types of secondary power. The secondary (standby) power supply is required to supply energy to the security system in the event of total failure of the primary (main) power supply or when the primary voltage drops to a level insufficient to maintain functionality of the control equipment and security system components.

According to NFPA 731, if primary power is lost or incapable of providing the minimum voltage required for normal operation of the security system, the secondary power supply shall automatically supply power to the system without loss of signals or causing transmission of an alarm.

Section 4.4.3.4 covers permissible secondary power supply sources.

Below is a sample of NFPA 731. For the complete section, see the actual NFPA 731 text at NFPA.ORG. Once there, click on the free access link to the latest edition of NFPA 731.

4.4.3 Secondary Supply.

4.4.3.1 The secondary (standby) power supply shall supply energy to the system in the event of total failure of the primary (main) power supply or when the primary voltage drops to a level insufficient to maintain functionality of the control equipment and system components.

4.4.3.2 When primary power is lost or incapable of providing the minimum voltage required for normal operation, the secondary supply shall automatically supply the power to the system without loss of signals or causing transmission of an alarm.

4.4.3.3 For an integrated system, the secondary supply capacity required by 4.4.1.4 shall include the load of all premises security–related equipment, functions, or features that are not automatically disconnected upon transfer of operating power to the secondary supply.

4.4.3.4 The secondary supply shall consist of one of the following:

(1) A storage battery dedicated to the premises security system arranged in accordance with 4.4.4

(2) An individual branch circuit of an automatic-starting engine-driven generator arranged in accordance with 4.4.5 and storage batteries dedicated to the premises security system with 15 minutes of capacity under maximum alarm load

(3) An emergency generating system as defined in NFPA 70, Article 700

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NFPA 731 Secondary Supply.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true regarding the secondary supply?

A: All security systems require two sources of supply.
B: Only storage batteries can serve as a secondary power source.
C: The secondary supply can be a storage battery dedicated to the premises security system.
D: Emergency generating systems are not permitted to be a secondary source of power.
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