Pass/Fail Criteria for Fire Alarm Battery Test?

9/14/2020

NFPA 72 requires a battery test be run including removal of the main power supply, waiting the full-length standby time, then activating the fire alarm system for the full alarm time. After the alarm time, the battery voltage is required to be tested.

What is the pass/fail mark for the battery voltage?

In theory, if the battery output still has 20.4 V, then the last appliance on a NAC circuit would still get a minimum of 16 V and everything still functions correctly. I just can't seem to find a code reference whether 20.4 V is the correct voltage to use (where a voltage reading below 20.4 V fails the battery).

Thanks in advance.

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4 Comments

Chris D

9/14/2020 10:44:29 am

I would refer to NFPA 72 10.6.7.2.1 which requires the system to operate. I would then refer to UL864 for the minimum operating ability of receiving 20.4VDC input on the batteries to pass UL as a minimum and may allow a particular manufacturer to show operation at a lower point (but this is very difficult to accept due to battery "knee")

Douglas link

9/14/2020 10:56:16 am

Because the batteries are part of the fire alarm panel and was tested and listed as a system by UL, ULC, FM, CE, etc., the manufacturer has determined the exact voltage that is needed.

Because each manufacturer requires a slightly different voltage for the minimum battery voltage, you will have to contact technical support for the manufacturer of the panel you are working on to determine the exact minimum voltage for the batteries.

Brian Gerdwagen FPE

9/14/2020 11:32:21 am

You are correct, most of the time. 20.4VDC comes from NFPA 72 85% of nameplate voltage. 24VDC nameplate requires a minimum 20.4VDC for secondary power in the battery. The installing contractor needs to perform voltage drop calculations that start at 20.4VDC to ensure the last devices receives 16VDC, or what ever the minimum UL voltage is.

NFPA 72 does not specify these numbers as different manufacturers have different nameplate voltages for the circuits and minimum voltages for the devices. Simplex has/had a system that used a boost converter to change the 24VDC to 29VDC because their devices had a higher voltage requirement. The battery would be the same, but you had to measure the 85% at the boost converter output, not the battery.

Pete D.

9/14/2020 12:54:30 pm

Most of the modern batteries you will encounter are the 12VDC 7 ah batteries. I have 52 local buildings and another 52 elsewhere in the US. You can get these on sale at ADI stores for about $12, and cheaper if you go through batterysharks.com. I just ordered 40 of them. I got a $20 battery tester on Amazon. If it fails a load test, it fails. They should be dated when installing with a Sharpie. If they are 3 yrs old, they get changed regardless. Sometimes they go into NAC power supplies, like the PAD3. If the battery is in a notification appliance extender, always replace with matching or higher Amp hours, as those have battery calcs that correspond to the circuit.

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