Clear-Com SB-704 - Manual (Page 22)

S B - 7 0 4 M A I N S T A T I O N 2 - 4
Figure 2-3: Fail Safe Power Distribution
The illustration above shows the proper power wiring of a system powered by
a single SB-704. The single-channel remote stations are connected to the ten
switched intercom connectors. These connectors derive their DC power
internally from the SB-704. The station comes set from the factory with the
power on the assigned lines #1 - #5 connected to channel A's power. The
power for channels #6 - #10 is sourced from channel B. Multiple-channel
remote stations are connected to the four intercom channels. In the case
above, a short on any one line will only take that channel down.
It is assumed that none of the power lines are interconnected in the external
system wiring. However, if a multiple-channel remote station that has not
been equipped for power line isolation is connected, those channels would
now have their power lines connected. The system will still work except that a
short circuit on any of the interconnected channels will cause both to fail thus
taking more of the system down with a single short circuit.
INTERCOM CABLE CONSIDERATIONS
The Clear-Com intercom line is intended to run on shielded-pair cable. One
conductor carries audio, the other conductor carries the DC power for remote
stations. The shield is used for ground return for audio and power. When
choosing interconnect cable, keep the following considerations in mind:
1. DC resistance of the ground or common conductor affects crosstalk. For
runs longer than 500 ft. (152.5 m) do not use wire smaller than 20 gauge.
2. The capacitance of the interconnect cable affects system frequency
response and sidetone stability. Total capacitance should not be greater
than 0.25 uF.
SB-704
RM-704
Remote
Station