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The volume of the call signal is affected by the volume control on the receiving unit, so if the volume is turned all the
way down at a receiving station, the call signal will not be heard. To avoid this problem, the call dry contacts can be
utilized to drive an external signalling device.
CALL DRY CONTACTS TO EXTERNAL DEVICE:
Depressing the call button also closes a normally open dry contact rated at 0.4 amps at 125 Vac or 1.0 amp at 24
Vdc. This contact can be used to trigger a remote sounder or light in order to accent the call feature. The wiring
diagram illustrates how an external light or horn can be wired in to augment the call tone. (See Figure 10).
MICROPHONE OPTION:
Keying the microphone (PTT) places the intercom in talk mode with the microphone over riding the speaker. A hand
held noise cancelling microphone is recommended when operating in loud ambient environments.
An optional hand‑held microphone conversion kit (Part No. K8502016) is available for Model 310‑MV. This field‑
installable kit includes a new cover plate with a 1/4" microphone jack and a microphone.
Units with optional microphones are not UL Listed for use in hazardous locations,
Marine, or Type 4X enclosure ratings. Units with the optional microphone
24VDC:
When connecting the intercom to 24 volts DC, either the positive (+) supply conductor must be fused at the source
with a 1/2 A fuse or a power‑limited power source must be used.
The 310 is capable of sending DC power to another unit that is mounted in a remote location without local power.
24VDC is available from pins 4 and 5 of the terminal block. It can be run along with the signal lines to an intercom in
a remote location. Only one unit should share the power supply of another unit in any installation.
Connect positive (+) supply conductor to pin #4 of terminal block. Connect the negative (‑) supply connector to pin
#5 of terminal block.
Figure 11 in the wiring diagrams section shows how two intercoms can be hooked up if no remote power is
available.
ISOLATED BALANCED/UNBALANCED LINES:
The audio signals for the 310 are transmitted over a wire pair using balanced line technology. This means each
wire carries a signal that is opposite in polarity of the other. At the input of the intercom is an isolated balanced line
transformer. This transformer subtracts the two signals from each other providing an output free of noise generated
onto the wires by some other noise source such as a motor or light fixture near the wires.
The isolation provided by the transformer means that the grounds of the units are not connected by the audio lines.
Therefore, ground loops and other problems caused by non‑isolated systems are avoided. The polarity of the audio
lines between the (+) and (‑) signal terminals need not be maintained.
A shielded cable can be used in installations where extreme problems from interference are suspected. The shield
should always be connected to the ground of only one of the intercoms. Connecting the shield to ground at both
ends will cause ground currents to travel through the shield which could cause hum in the system.
There are several diagrams in the back of the manual to aid in wiring intercoms together. The wiring diagram section
illustrates balanced and unbalanced line interconnection along with how a shielded audio cable can be used. (See
Figures 12 through 15.)
It also illustrates multiple intercom interconnections.
SURGE PROTECTION:
Metal Oxide Varistor (MOV) devices are used to protect the audio lines and the remote control line. The intercom
must have Earth Ground terminated to it to ensure surge protection.
The output amplifier of the 310 offers full short circuit protection and over heat protection.
should be used only in indoor applications.
NOTE
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