Douglas Krantz - Technical Writer - Describing How It Works

How do We Make the Conventional Sounder Bases Work?

By Douglas Krantz | Maintenance

How do We Make the Conventional Sounder Bases Work?

How do We Make the Conventional Sounder Bases Work?

Greetings Douglas,

I am having a difficulty with a conventional fire alarm system with sounder bases (SB). The sounder bases are installed with conventional smoke detector in every sleeping room.

However, when we activate the building fire alarm system, (say via Manual Call Point [MCP} or pull station in the hallway), they do not make a sound. They only make a sound individually when the smoke detector on the sounder base is activated into alarm. And it's that sounder base alone where the activated smoke detector is attached that makes a sound.

How to we make the all the sounder bases sound-off during a building alarm? Or is that even possible?

Thank you, LS

What you're describing is quite possible, but it takes thinking outside normal.

Sounder Bases

From one point of view, the sounder bases are just fire horns. There are, however, two ways of turning on the sound.

Normal Turn On: This would be the building's fire alarm sounding a general alarm throughout the building. When the power supplied by the Notification Appliance Circuit (NAC) is sending forward voltage; the blocking diode inside the horn allows current to pass through the fire horn, sounding the alarm. When the general alarm is not sounding, the voltage is reversed; the blocking diode inside the horn is preventing current from passing through the horn, and it remains silent. This is how all the horns (and sounders) in the building are turned on and off.

Smoke Detector Turn On: Whether the NAC has forward voltage, or reverse voltage, the smoke detector plugged into the base can turn on the fire horn.

Continuous Power

The power supply is providing power when all the horns (sounder bases) are sounding the general alarm, and the power supply is also providing power so the individual horns (sounder bases) can sound their local alarms. This means that the power supply cannot switch to a low power supervisory voltage at any time; the power supply has to provide full power all the time.

Reversing Relay: Commonly, this kind of voltage reversal is done with a "reversing relay". A reversing relay is mostly a standard double-pole, double-throw relay and uses a blocking diode to detect a general alarm. If the fire alarm manufacturer for the system you're using can supply one, that is a good place to locate it.

Wire Supervision

The wires for the sounder base fire horns usually have to be wired as a Conventional Class B NAC circuit. Instead of an end of line resistor, though, an end of line device (usually a relay) has to be used. This relay is held in the active condition by the voltage on the sounder bases' NAC circuit. If the power is ever lost to the end of the line, the relay relaxes, and opens up the wires to the smoke detectors' end of line resistor.

When opening up wires, all smoke detectors have to remain able to send alarms, so it is only the wires to the end of line resistor that can be opened up.

Call Technical Support

I've described one method that has been used, but this is a method that was approved by a different fire manufacturer than the one you have there. You will have to call their technical support team to find out how you can do it with your system.

Remember, all fire alarm systems have to be listed. Ask the manufacturer to find out if that system is listed to work with the sounder bases.

While talking to them, see about being able to connect all the sounders in a residential unit together, so if one goes off in one bedroom, all the sounders go off in the residential unit.

Douglas Krantz
Life Safety
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