Power Supply Trip Via NAC : UL 864 9th Edition

A collegue and I are having a discussion regarding multiple remote power supplies tripped via the same conventional notification circuit.

He is saying that there are now UL 864 9th edition remote power supplies out there that, if tripped via a conventional notification circuit, can close the trouble contact during an alarm, allowing both the first remote power supply and the next power supplies in line to activate upon an alarm condition.

I’m not talking about tripping them via control module, tripping by communication wiring, just tripping via one conventional nac circuit.

I’m of the opinion that he is reading more into the manuals than it actually says. One power supply prior to UL 9th edition says “when controlled with conventional NAC inputs, common troubles are signaled by providing an open circuit that disconnects the NAC wiring from its end-of-line resistor but still allows a reversed polarity alarm to be received.” To me this only says that if one power supply is wired to trip via a NAC circuit, the trip input will work and trip the remote power supply even if something on the power supply is in trouble, thus opening the circuit on the trip out.

I am of the opinion that any second or third power supply down the line will not work, as seen on typical power supplies tripped via one NAC. I am of the opinion that they can meet UL 9th edition by tripping via other methods, such as control module, but not this way. Are there exceptions to this rule? Please send specific make and model.

Thanks
FireChick
Tampa, FL
New Forum Member

These daisy-chained NAC panel situations make my head hurt. Just to make sure I understand what you are describing: you have a single class B NAC passing in and out of several NAC panels as the trigger circuit for all of them? In this case, I don’t think you can wire these in such a way that a trouble on one NAC panel will not disconnect all the NAC panel triggers downstream from it. Maybe some manufacturer has devised a trigger circuit that automatically re-closes the supervision circuit when it senses alarm polarity, but I highly doubt that such a thing exists. Most NAC panels I have seen have documentation saying the resistor must be installed directly after the trigger contacts.

This is an inherent issue with class B conventional circuits. It is true that when one notification appliance is pulled down, the rest of the circuit cannot sound in an alarm. It becomes much more of an issue when NAC panels are involved, though, and the whole thing can make troubles a nightmare to track down. This is not an issue with class A circuits, though I don’t know the code specifics of combining NAC panel triggers with other devices in this situation. It still doesn’t seem like a good idea.

One way you could wire the NAC panels that avoids this issue is to properly daisy-chain them, as in have the NAC panel trigger as the last device on the FACP NAC, then dedicate the last circuit from the NAC panel as the trigger for the next NAC panel. This way, each NAC panel trigger is at the end of the NAC, right before the resistor.

I really wish more manufacturers offered addressable NAC panels with system-wide sync. So the panel could actually tell you the precise circuit that is in trouble, and you wouldn’t have to worry about visual zones.

This would probably make a lot more sense with pictures. Let me know if this makes any sense at all.

In the case of hardwired serial connected NAC extenders to be able to bypass the trouble contact all it takes is a diode connected across the contacts. The relay can open the host panel NAC to report trouble. When the host panel goes into alarm the polarity reverses and the diode would bypass the open relay contact passing the alarm polarity to the other NAC extenders. That is the way Simplex 4009 NAC extenders are designed.

Wow! Maybe that is the case with some of the NAC panels I work with. You’re right that it would only take a diode. I had been working under the assumption that that wasn’t the case, but I will have to check now and see if I was wrong about that. I mainly work with the various Honeywell brands.

i’ve only ever used power supplies with separate trouble contacts. you can route the circuit through the activation inputs on all NAC panels, and then route it back through the trouble contacts. easy as pie. or route the circuit through the activation inputs on all the NAC panels, and stick a monitor module on the trouble contacts on each one.

addressable NAC panels are amazing too though. simplifies wiring, awesome for trouble shooting, and gives massive control over each circuit.

1 Like

Hi Chris,

I have an installer that likes to wire the remote power supply’s through the inputs only with the resistor at the last power supplys input. I have been finding NAC power supply not being supervised and I think it’s because it’s the way he is wiring them. It has to be also ran through the trouble contact as well correct?