52 Chapter 2 Introducing the BCM50 hardware
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The cooling fan mounts in the back of the BCM50 enclosure.
For information about how to install or replace the cooling fan, refer to “Replacing an internal
component” on page 189.
RJ-21 telephony connector
Use the RJ-21 telephony connector to connect a 25-pair (RJ-21) cable to the main unit. These 25
pairs of wires are then connected to the following telephony devices (see “RJ-21 telephony
connector wiring chart” on page 205):
• 4 analog lines
Use these connections for analog trunks from the Public Switched Telephone Network
(PSTN).
• 4 analog telephones
Use these connections for analog telephony devices such as single line telephones, fax
machines, and modems.
• Auxiliary ringer
Use this connection for an auxiliary ringer (customer supplied). The BCM50 system uses the
auxiliary ringer to control the cadence of an auxiliary ringer. You must use this output in a low
current, low voltage application only. Do not use this output for switching the auxiliary ringer
directly.
• Page output
Use this connection to connect an internally generated voice paging signal to an external
paging amplifier (customer supplied).
• Page relay
When you use the page output to connect an external paging amplifier, you also use the page
relay. The page relay connects to a floating relay contact pair. The BCM50 system uses the
page relay to control the external paging amplifier.
• Music input
Use the Music input to connect an external music source that supplies a signal to held lines
(music on hold) or telephone speakers (background music). The input source can be any
available radio or music source approved for connection to the network. If you use this
connection, do not use the Music input jack on the main unit faceplate.
• 12 digital telephones
Use these connections for digital telephones. For a list of digital telephones that are compatible
with the BCM50 system, refer to “Telephones and adapters” on page 54.
Warning: External equipment connected to the auxiliary ringer, page relay, page output,
and music-on-hold interfaces must use safety extra low voltage (SELV).
All four interfaces are SELV and the external equipment connected to these interfaces
must be SELV. If these interfaces are not SELV, you must use external line isolation units
(LIU).
