User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.
7
8.0 CABLING
For the PRO Series Intercom system the interconnecting
cables are of the shielded two-conductor microphone cable
type and the intercom line connectors are of the XLR-3
type. Audio and Call signals are on XLR pin 3, DC power is
on XLR pin 2. XLR pin 1 is connected to the shield of the
cable which functions as the common return for audio and
power.
Since the audio signal is transferred in an
unbalanced
way, certain rules have to be obeyed when installing the
cables of an intercom network. This is to avoid earth loops
and to minimize power loss and the possible effect of
electromagnetic fields.
These rules are:
• Use high quality (multipair) cable.
For interconnecting user stations, power supplies
and accessories in an ASL Intercom network, use
high quality shielded two-conductor (minimum 2x
0.30 mm2) microphone cable only.
In case of a multi channel intercom network, use
high quality microphone 'multipair' cable only, each
pair consisting of two conductors (minimum 2x 0.15
mm2) with separate shield. Multipair cable should
also have an overall shield.
• Use flexible cables.
Use flexible single and multipair microphone cable
instead of cable with solid cores, especially when the
cable is subjected to bending during operation or
installation.
• Separate cable screen to XLR pin 1.
The screen of each separate microphone cable
and/or the screen of each single pair in a multipair
cable, should be connected to pin 1 of each XLR-3
connector. Do not connect this cable screen to the
metal housing of the connector or to metal wall
boxes (outlets).
See page 12 for Earthing Concept.
• Cable trunks, connection boxes and overall
multipair cable screen to clean earth.
Metal cable trunks, metal connection boxes and
overall multipair cable screen should be inter-
connected and, at one point (the 'central earthing
point') in the intercom network only, be connected to
a clean safety earth.
See page 12 for Earthing Concept.
• Keep metal connection boxes and cable trunks
isolated from other metal parts.
Metal housings for intercom cables and connectors
should be mounted in such a way that they are
isolated from other metal cable and connector
housings and from any other metal construction
parts.
See Party Line, Technical Concept
• Keep cables parallel as much as possible
When two (multi channel) units in a network are
connected by more than one cable, make sure that
these cables are parallel to each other over the whole
distance between those units. When using multipair
cable, parallelism is ensured in the best possible way.
• Avoid closed loops.
Always avoid that cables are making a loop. So-called
'ring intercom' should not physically be cabled as a ring.
All cable routes should have a 'star' configuration, with
the central earthing point (usually close to the power
supply position) as the centre of the star.
• Keep cables away from electromagnetic sources.
Keep intercom cables away from high energy cables,
e.g. 110/220/380V mains power or dimmer controlled
feeds for spotlights.
Intercom cables should cross high energy cables at an
angle of 90
°
only.
Intercom cables should never be in the same trunking
as energy cables.
• Place power supplies in a central position.
In order to avoid unacceptable power losses, place the
power supplies as close as possible to where most
power consumption occurs or, in other words, most user
stations are placed.
• Connect ASL power supply to a 'clean' mains outlet.
The ASL power supply may be connected to the mains
power outlet to which other audio equipment is
connected. Avoid using mains outlets which also power
dimmer controlled lighting systems.
In case of more complex installations, don't hesitate to
contact us. Please send us a block diagram of the
planned network with a list of all user stations and their
positions, and we are happy to advise you on cabling
lay-out.