Clear-Com PS-704 - Manual (Page 21)

P S - 7 0 4 F O U R - C H A N N E L P O W E R S U P P L Y
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cables or headset “Y” cables, as they will increase crosstalk into a
multi-channel system.
INTERCOM CABLE CONSIDERATIONS
The Clear-Com intercom line is intended to run on one shielded cable pair per
intercom channel. One conductor carries audio, the other conductor carries
the DC power for remote stations. The shield serves as the ground return of
the audio and power conductors. When choosing interconnect cable, keep the
following considerations in mind:
• Keep cable runs under 500 ft. (152.5 m). The DC resistance of the
ground or common conductor affects crosstalk. For permanent installation
runs longer than 500 ft. (152.5 m), do not use wire smaller than 20 gauge.
The capacitance of the interconnect cable affects system frequency
response and sidetone stability. Total capacitance should not be greater
then 0.25 uF.
• Portable installation cable: Practical cable for portable system
interconnections is flexible, two-conductor, shielded microphone cable.
We suggest using Belden #1800. For runs longer than 500 ft. (152.5 m),
use a 20 gauge cable or larger (Belden #8412).
• Permanent installation cable: Vinyl-jacketed shielded pair is the cable
of choice for permanent installations. Placing the cable in conduit is
recommended, but not necessary.
• Multi-pair cable: Individually shielded multi-pair cable is acceptable for
use in multi-channel systems. For cross-talk considerations the shields
must be tied together on both ends of the cable to produce the lowest
possible DC resistance path for the ground return.
• Grounded installation: The pin #1 ground connection of each XLR
connector must also be isolated from the chassis. Pin #1 should not be
connected to the shell of the XLR connector.
• Suggested cable types: The following chart lists the specifications of
various BELDEN cables:
Table 2-1: Belden Cable Types
Trade
No.
No. of
Pairs
AWG &
Stranding
Insulation
Thickness
(inch)
Jacket
Thickness
(inch)
Nom. O.D.
(Inch)
Nom
Cap(
p
F/ft)
Shield Nom
D.C.R.
(Ohms)
8413 1 24 (45x40) 0.019 0.025 0.019 30
8412 1 20 (26x34) 0.02 0.043 0.268 30
8762 1 20 (7x28) 0.014 0.028 0.196 27
8760 1 18 (16x30) 0.018 0.028 0.222 24
1408B 4 24 (7x32) 0.04 0.037 0.346 31 4.8 Ω/Μ
1814A 2 22 (7x30) 0.05 0.025 0.319 31 3.9 Ω/Μ