A-A-50796A
3.1.3.5.2 Speaker wires. Interconnecting speaker wire shall be, at minimum, 18 AWG stranded wire conforming to the requirements of 3.1.2, and a minimum of 15 feet long, unless otherwise specified (see 7.3(e)).
3.1.4 Circuit design. The electronic siren shall be constructed to use a floating ground return and shall not use the chassis for ground return. The siren shall not be required to operate on reversed polarity power connections, but shall not be damaged by such connections.
3.1.4.1 Power isolation. The amplifier's output shall be isolated from the primary input power by a transformer to prevent shorting the battery or damaging the internal components of the electronic siren in case the output becomes grounded.
3.1.4.2 Circuit protection. Internal circuit protection shall be provided by a fast- blow fuse
(15 amps) or circuit breaker.
3.1.4.3 Operating current requirements. a. Class A siren.
(1) Maximum standby current shall be 0.5 amp.
(2) With one speaker (driver), the maximum current shall be 6 amps.
(3) With two speakers (drivers), the maximum current shall be 12 amps. b. Class B siren.
(1) Maximum standby current shall be 0.6 amp.
(2) With one speaker (driver), the maximum current shall be 4 amps. (3) With two speakers (drivers), the maximum current shall be 6 amps.
3.1.4.4 Public address (PA) system. The minimum input required for operation of the PA
system shall be 0.55 volt root-mean-square (rms) into an average load of 8 ohms.
3.1.5 Electromagnetic compatibility. Siren equipment provided to the government under this
CID shall be compatible with radio communications equipment used on first-responder vehicles.
3.1.6 Environmental requirements. The siren shall be operable in the temperature range from
-40 °C (-40 °P) to 70 °C (158 °P) and shall be designed to withstand a relative humidity up to
100 percent. The siren shall be designed to withstand vibration for a period of at least 1 hour at
12 Hertz (Hz) ±1 Hz, 0.3 centimeter (0.125 inch) peak-to-peak displacement. All speakers shall be weatherproof.
3.1.7 Modes of operation. The following modes of operation shall be selectable by controls on the front panel of the amplifier assembly. These modes shall be clearly marked as indicated:
a. Public address (PA) mode. This mode connects the microphone to the amplifier for use as a public address system. This mode shall be marked as "PA".
b. Radio mode. This mode amplifies calls received on a vehicle two-way radio through the PA system. This mode shall be marked as "RADIO".
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