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Can I Use a NAC Circuit for a Sounder Base?

The NAC circuit (Notification Appliance Circuit) can't be used for the sounder base because the NAC circuit is an On-Off circuit and the sounder base requires an On-On circuit.

The sounder base requires power to be fully on with a building alarm, and fully on when standing by

Greetings Douglas,

Can I connect sounder base of smoke detector (in sleeping room) to NAC circuit?

Thank you, HB

On-Off NAC

Used to power the horns and strobes in the hallways of the building or power for the minihorns in the apartments, a NAC circuit provides full power only when sounding the alarms in the entire building. When it isn't sounding the alarms, the NAC circuit reverses voltage, and at the same time turns into the equivalent of an Ohmmeter to check the wires (supervise the wires). When the voltage on the NAC circuit is reversed so it's supervising the wires, the NAC circuit doesn't provide enough power for anything.

On-On Sounder Base Circuit

When the horns and strobes in the hallways of the building are sounding the alarm, the sounder base circuit is providing full power to the sounder base. Think of the sounder base as a building-wide minihorn for the sleeping room.

When the horns and strobes in the hallways of the building are not sounding the alarm (the alarm is silent), the sounder base circuit is still providing full power to the sounder base. That is so the smoke detector can turn on the sounder base when the rest of the building is silent. Think of the sounder base and the attached smoke detector as a residential smoke alarm.

For the sounder base to sound when the whole building's alarms sound, the polarity on the sounder base circuit is one way; for the sounder base to sound the alarm when only its smoke detector is in alarm, the voltage on the sounder base circuit is the other way.

The Sounder Base Requires Full Power All the Time

Whether or not the building's fire alarm system is in alarm. the sounder base circuit has to provide full power to the sounder bases in the building at all times.

Douglas Krantz Douglas Krantz


Question

Mr. Krantz

Question: Is the Simplex sounder base an exception to the rule regarding using NAC circuits for sounder bases? Don't they have the option of using the NAC circuit power in an alarm?

Thank you, GC

Most NAC circuits (Notification Appliance Circuits) on most fire alarm systems are ON-Off circuits.

ON: When the alarm is sounding throughout the building, the NAC circuit is providing power (and lots of it) to power all the horns and strobes in the zone being covered by the NAC circuit.

OFF: When the alarm is not sounding, the voltage on the NAC is reversed, an a very low power supply is checking continuity on the circuit. The circuit usually has lower voltage (sometimes less than 2 volts) and this voltage is only used to check the continuity of the wires (supervise the wires).

The smoke detector's sounder base has to sound the alarm when the NAC is on - when the building is in alarm, and the smoke detector has to turn on the sounder base when the NAC is off - when the panel is supervising the wires. Most NAC circuits will not provide enough power for the sounder base when the NAC is off.

Simplex Exception

I haven't worked much with Simplex designs, but Simplex often has differences in their designs. What they refer to as a NAC circuit may be less of the NAC circuit that most manufacturers use and more of a supervised power circuit (no voltage reversal). If it's a supervised power circuit, it's an ON-ON circuit - never turning off. The key to this is found in their installation literature for the sounder bases.

Important to this is if there are any questions on what can and can't be used, talk to the Simplex technical support people. They know their system and will give better answers about their system.

Douglas Krantz Douglas Krantz
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer
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facpdoug@douglaskrantz.com
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