Fire Alarm Panel

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Nardie

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North Augusta, SC USA
So I was informed today that the main fire alarm panel I have is overloaded due to the number of power supplies in the panel. The fire alarm panel has five power supplies that could require if fully loaded 5A each, and it is protected by a 20A breaker from the lighting panel. Therefore, 25A and the 20A breaker would trip. However, during annual testing of the fire detection circuits, which activates all devices, there has been no issue. We don't record the amps during this test because it is not required. We are planning to do this to see the actually amp draw. So my question is, if the amp draw is below 20A is it acceptable to have a 20A breaker protect equipment that could exceed the 20A? When I look at the NEC it provides maximum protection, not minimum. Also, this seems to me to like a lighting panel with a 100A breaker, yet when I look at the VA load on the panel schedule it would be overloaded. Yet, we all know load diversity and other factors should be considered. So, I appreciate any thoughts.
 
1) You need your own code book:
NFPA-70, ARTICLE 760 Fire Alarm Systems

2) Lookup:
760.45 NPLFA Circuit Overcurrent Device Location.

3) Read:
Exception No. 2:
 
Exception 2 clarifies low voltage power-supply output is not the same as line-voltage input.
 
If my math is correct, a 24v power-supply output divided by 120v line-voltage input equals 0.2

If I understand how to apply this ratio, then Amp-clamp metering the branch circuit during full load of power-supply output(s) should measure line voltage power at 20% of Low voltage power output.
 
Nardie said:
When I look at the NEC it provides maximum protection, not minimum. Also, this seems to me to like a lighting panel with a 100A breaker, yet when I look at the VA load on the panel schedule it would be overloaded. Yet, we all know load diversity and other factors should be considered. So, I appreciate any thoughts.
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I'm with you in that I don't see how 760.45 applies.

I would recommend if you have an as-built circuit diagram showing how many devices are on each power-supply and show their loads on each, maybe you would have a case because the system is already installed. Have you reviewed 760.51, because this may raise some flags after your findings?
 
Nardie said:
So I was informed today that the main fire alarm panel I have is overloaded due to the number of power supplies in the panel. The fire alarm panel has five power supplies that could require if fully loaded 5A each, and it is protected by a 20A breaker from the lighting panel. Therefore, 25A and the 20A breaker would trip. However, during annual testing of the fire detection circuits, which activates all devices, there has been no issue. We don't record the amps during this test because it is not required. We are planning to do this to see the actually amp draw. So my question is, if the amp draw is below 20A is it acceptable to have a 20A breaker protect equipment that could exceed the 20A? When I look at the NEC it provides maximum protection, not minimum. Also, this seems to me to like a lighting panel with a 100A breaker, yet when I look at the VA load on the panel schedule it would be overloaded. Yet, we all know load diversity and other factors should be considered. So, I appreciate any thoughts.
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Are these power supplies drawing 5A at 120VAC, or supplying 5A at 24VDC?
 
That's right, Art. 760 describes NPLFA circuits. I've never recognized those devices in the field, and did not consider it.
That means NPLFA power supply output Amps would be same as branch-feeder amps.
 
ramsy said:
That's right, Art. 760 describes NPLFA circuits. I've never recognized those devices in the field, and did not consider it.
That means NPLFA power supply output Amps would be same as branch-feeder amps.
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Where is anyone talking about NPLFA circuits?? It is highly unlikely, in this day and age, anyone is installing NPLFA's, except for the oddball amplifier module like the Siemens ZAM-180.
 
What else could Texie be referring to in post #9, except line-voltage controls, and NPLFA circuits for 480 volt fire pumps?
 
ramsy said:
What else could Texie be referring to in post #9, except line-voltage controls, and NPLFA circuits for 480 volt fire pumps?
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Seriously? Re-read #9 carefully; "resi burg/fire panel", "commercial fire panel". Where is "480 volt", "NPLFA", and "fire pumps" mentioned? Or the OP; "the main fire alarm panel". We're either talking line side 120VAC to the panel power supplies, of which there are 5, or the 24VDC load side of those power supplies.
 
Then what's wrong with calling power supplies wall worts in post #8 ?

Or pointing out in post #2, 4, & 5 that voltage transformers, by any other name, don't measure the same line vs load Amps ?
 
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