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
2 - 7
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
1815A
4
22 (7x30)
0.05
0.03
0.384
31
3.9
Ω/Μ
