What does "power limited circuit" mean?

I’m resting the manual for my new panel and this is all it says for all the NACs. What the heck does this mean? Also,

With a Fire Lite MS-5UD-3 Panel, if two wires on a NAC short, will this break the panel, or will it just result in a trouble. This happens in my system occasionally cuz I’m clumsy (lol). I just want to know to be more cautious.


I’m not sure, because the 4004 uses a different terminal type, except that Simplex references the same thing in their manual as well. I think it has something to do with the NAC output or something.

Power-limited wiring refers to a circuit whose voltage is inherently limited. For fire alarm panels, the circuit voltages are limited to 24V by the transformer, hence the designations as a “power limited circuit.”

Non-power limited circuits, such as household 120V circuits, are subject to potential voltage surges, overcurrents, etc.

So if I short a NAC it WONT be damaged?

If I’m not mistaken, the 5UD has non replaceable NAC fuses, so if you do short it you’ll likely blow it and cause a permanent trouble/non-usable NAC.

Yes, what Jack said is correct. Some panels have removable NAC fuses, and others like these do not.

Some panels will be able to detect a short and shut down the NAC before any damage occurs, but it is never a safe practice to allow shorts to happen.

A direct short is in fact one example of how these power-limited circuits are beneficial: rather than drawing high currents through the short and potentially resulting in further damage to the board or a fire, the circuit will be protected by the fuse.