What you have noticed in the NFPA Code about testing appears to address a very important issue; the issue is that in some fire alarm systems, the primary power supply isn't adequate.
Apparently, there has been a real problem. In other words, it seems that in a few systems, the batteries have failed when there was a real fire. When the batteries failed during a real fire, even though utility power was being used, some occupants of a building weren't notified. Now, the NFPA want you to test for this.
Two Independent Power Supplies
In a fire alarm system, there are actually two power supplies: a primary source of power and a secondary source of power. In most fire alarm systems, the primary source of power is derived from utility power, and the secondary power source is the standby batteries.
In order for each source of power to be truly separate, one power supply cannot depend on the other power supply. If one power supply completely fails, the other power supply still has to be able to keep the whole fire alarm system working, especially when there's a real fire.
If the primary source (utility power) depends on the addition of power from the batteries, there is really only one source of power: the utility power plus the supplemented battery power. Because of this dependance, if the batteries fail, then the fire alarm system fails.
If there is a code in the NFPA code that says that this possibility should be tested, there have been failures caused by technical problems with some fire alarm power supplies. Or worse, some manufacturers are just not following other parts of the code.
You have me intrigued.
Yes, the NFPA has addressed this for many years. In other words, for a long time, the NFPA has said that this is important; the NFPA recognizes that there really is a problem.
The NFPA 72 Code, Version 2007, in the Index, under the category "Power Supply", sub-category "Primary", there is a reference to Code 4.4.1.3.1 (Look it up for yourself, your version might have a different code number.)
4.4.1.3.1 - At least two independent and reliable power supplies shall be provided, one primary and one secondary, each of which shall be capable of adequate capacity for the application.
To me, the code means that the entire fire alarm system should be capable of fully operating with its primary power source, alone, even when the battery (the secondary power source) is unplugged.
The same goes for the secondary power supply (batteries). The entire fire alarm system should be capable of fully operating with its secondary power source, alone, even when there is a neighborhood-wide power outage.
That's what the words "independent and reliable" means.
Before I received your email, I never imagined there was an issue with puny fire alarm power supplies; now I know better.
Douglas Krantz
