Listed for Use
Cascading Notification Appliance Power Supplies is often an issue. With synchronization signals riding on top of the DC power on Notification Appliance Circuit, the second power supply in the cascade may never turn on, even during a fire.
Look up in the installation manual for the power supplies. The wiring diagram is the diagram used when the testing-laboratories like UL, ULC, FM, CE, CCC, etc. tested the power supply to see if it worked. After the laboratories determined that the power supply worked, then they placed the power supply on their list of equipment that was "Listed for Use".
If the wiring is different, like if the Supplemental Notification Appliance Circuit Power Supply (SNAC) is connected to another SNAC, the second one may sometimes work, or it may not work at all. Any other wiring has not been tested, and is not "Listed for Use".
Use the diagrams supplied in the Installation Manuals that come with the SNAC, and the Installation Sheets that come with the Addressable Module. Make sure that the word "Installation" is in the title of the manual or sheet.
Stand-Alone
For powering the horns and strobes, the Fire Alarm Control Panel and the Supplemental Notification Appliance Circuit Power Supplies are stand-alone power supplies. Each one, by itself, powers two to four Notification Appliance Circuits (NACs).
Each one, for its primary source of power, is connected to the building's utility power, and each one, for its secondary source of power, has backup batteries.
Fire Alarm Control Panel NAC Power Supply
The relays inside the FACP and the SNAC panels for the NAC outputs are mechanical switches. Other than being operated by an electromagnet inside the relay, there is no difference between a relay and a light switch on the wall.
Wire Supervision
When the fire alarm system is not in alarm, the wires carrying power on the NAC circuit are being supervised by the supervision circuitry inside the panel.
Alarm
When the panel goes into alarm, the wires carrying power on the NAC circuit are connected to the panel's 24-volt power supply.
As a side note: this is where the "Alarm Voltage Reversal" comes from. When the NAC circuit is being supervised, the relay is relaxed and the
positive wire of the NAC circuit is switched to the
negative supervision voltage, and the
negative wire of the NAC circuit is switched to the
positive supervision voltage.
When the panel goes into alarm, the relay is activated and the
positive wire of the NAC circuit is switched to the
positive power supply voltage, and the
negative wire of the NAC circuit is switched to the
negative power supply voltage.
Wire Supervision
The Addressable Control Supervised Output Module has a very similar relay. When the fire alarm system is not in alarm, the wires carrying power on the NAC circuit are being supervised by the supervision circuitry inside the module.
Alarm
When the panel goes into alarm, the wires carrying power on the NAC circuit are connected to the wires coming into the module.
As a side note: this is where the "Alarm Voltage Reversal" comes from. When the NAC circuit is being supervised, the relay is relaxed and the
positive wire of the NAC circuit is switched to the
negative supervision voltage inside the module, and the
negative wire of the NAC circuit is switched to the
positive supervision voltage inside the module.
When the panel goes into alarm, the relay is activated and the
positive wire of the NAC circuit is switched to the
positive external power supply voltage, and the
negative wire of the NAC circuit is switched to the
negative external power supply voltage.
Triggering the SNAC Power Supplies
Because the Fire Alarm Control panel sends 24 Volts DC to sound the alarm, without extra synchronization signals on its NAC output, the panel can be connected directly to the SNAC power supply.
The Supervised Output Control Module is a little different. The SLC's control module does not have an internal 24 Volt power supply, so it needs the 24 volts supplied by the same SNAC panel it's controlling.
Wire the Panels and Modules the Same Way They are Listed
Remember to wire the panels and the module exactly as shown in the diagrams in the Installation Manual and Installation Sheet. That's the wiring diagram that was used when the module and panels were being tested to be listed; that's the wiring method that actually works.
If there's still confusion about wiring, contact the technical support teams for the fire alarm control panel and the SNAC panels.
Before calling them, make sure you have the exact model of all panels. They'll ask for this information.
Douglas Krantz
