Clear-Com PS-704 - Manual (Page 17)

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WIRING
When considering how to wire an intercom system, several factors must be
taken into account. These include the number of stations, the length of the
cable runs and whether single or multiple channels are preferred. If
multi-channel stations are connected with multi-pair cables, then crosstalk
becomes an important issue. (Crosstalk is not a factor with single-channel
systems or multi-channel systems where each channel is run on its own
individual cable to single-channel remote stations.) While the physical
considerations include ease of installation, type of cabling, station location,
etc., the electrical considerations are concerned primarily with the capacitance
between conductors on the intercom line and the DC resistance in the ground
return of the intercom line.
Caution: Pin #1 and the shell of the XLR plug on the interconnect cables
should NOT be connected together.
Excessive resistance in the conductors of the cable results in a loss of sidetone
null at remote stations and some overall loss of level. Excessive resistance in
the ground connector or shield greatly increases crosstalk between channels.
This can greatly affect the performance of multi-channel systems.
SINGLE-CHANNEL SYSTEM
In a single-channel system, there are two general methods of wiring remote
stations to the power supply. Any one method may be used exclusively in a
small system and both may be used in various combinations for a larger
system.
1. Daisy Chain: Remote stations are wired from one station to the next and
so on along each line connected to the power supply. This requires the
least amount of cable, but may be impractical due to the system layout.
Also, if a break occurs in the line, all stations downline of the break will
be disconnected from the party line.
Figure 2-1: Daisy Chain
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