According to Annex A, “depending upon the design of the system, one or several power supplies can be used. The power supplies should be sized to provide adequate power for simultaneous use of all associated devices, such as readers, RTE motion detectors, locks, controllers, and so forth. Power calculations need not take into account simultaneous inrush current.

As a result of certain conditions, such as temperature, device inrush requirements, tolerances, and other environmental factors, it is recommended that power supplies be designed with a safety factor of 25 percent”.

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.

6.1.9 Power Supplies.

6.1.9.1 Power supplies shall meet the requirements of Section 4.4.

6.1.9.2 Power supplies shall be sized based upon the application and the manufacturer's requirements.

6.1.9.3 The voltage and current of the power supply shall be the same as required by the associated field devices.

6.1.9.4 Power supplies shall be installed in a space that protects them from damage, tampering, and access by unauthorized personnel.