Tyco 579-769 specifications 2.Class A and B Speaker Circuit Wiring

Parts of an Emergency Voice/Alarm Communications System, Continued

Speaker Circuits	Speaker circuits convert electrical power from amplifiers into sound. These circuits are wired in a
	daisy-chain fashion, with a single path of electrical continuity from the NAC to the last speaker in
	the circuit. The speaker circuits can be wired in Class A or Class B configurations. Class A
	operation allows the circuit to operate through a single Open, while Class B circuits only detect
	the Open. Neither circuit operates through a Short Circuit condition, but either can report the
	trouble.

Note: Speaker circuits are normally supervised with DC voltage during the standby or non-alarm state when the speaker circuits are OFF. To use speaker circuits for non-alarm paging or background music applications you must have approval of the AHJ (Authority Having Jurisdiction). Specially designed hardware is available to supervise speaker circuits when used for non-alarm content.

Speaker circuits are known as constant voltage systems, where a full volume output tone produce 25 V or 70.7 V. Wattage taps on the speaker sets the individual speaker volume. The designer can select from 1/4 W to 2 W in a typical fire alarm speaker.

	B+		Class A Wiring
Class A NAC	A+	Speaker	Speaker	Speaker
	A-
	B-
			Class B Wiring
Class B NAC	B+	Speaker	Speaker	Speaker
					End of Line
					Resistor
	B-

Figure 4-2. Class A and B Speaker Circuit Wiring

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