Federal Signal AudioMaster 310LD-MV Instrucciones De Instalación Y Servicio página 13

The dry contacts can be used to switch devices such as an auxiliary
sound or light when call is depressed. The maximum ratings for the dry
contacts are 0.4 amps at 125VAC and 1.25 amps at 24VDC. This method
assures a call is received even when the volume on one of the intercoms
is turned all the way down.
Intercom I supplies the DC power to the second intercom. Earth ground
must be wired on the second unit.
Using Call Dry Contacts with AC
Figure 7.
No Remote Power Available
Figure 8.
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