Cadac C-Type - Manual (Page 8)

1-2 Connecting the mixer systems
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Cadac consoles are designed to allow the use of two independent power supplies in
a redundant configuration – “main” and “backup”. Both power supply units are used
to power the console system so that under normal conditions, the ‘load’ is shared
between the “main” and “backup” PSU’s. If a fault occurs in one of the power units
(causing it to ‘shut-down’), the remaining power unit will power the console.
In situations where it is necessary to provide a separate ‘feed’ to each PSU, make
sure that the cable lengths are the same. This is to minimize any induced a.c. power
input noise by ensuring that the “EARTH IMPEDANCE” is the same for both PSU
systems.
The a.c.-input connectors on each power supply unit have three conductors: ‘LIVE’
(brown), ‘NEUTRAL’ (blue) and ‘EARTH’ (yellow/green). For safety and electromag-
netic compatibility considerations, it is essential that the ‘EARTH’ conductor is con-
nected on all PSUs and the a.c. supply has an ‘EARTH’ conductor that has a
continuous circuit to the “zero-signal reference potential” point in the building. The
ZSRP point in a building is usually found near the place where the a.c. ‘mains’ supply
enters the building (often referred to as the “MAIN GROUND REFERENCE EARTH
ELECTRODE SYSTEM”). The basic concept for correct a.c. mains wiring distribution
is shown in figure 1-1. If you need further information about this complex subject,
please refer to “Grounding Systems and their Implementation” by Charles Atkinson
and Philip Giddins published in the AES Journal Vol. 43, No. 6 – June 1995.
The grounding scheme in CADAC consoles is designed to meet the rigorous EEC
Electromagnetic Compatibility requirements (EMC Directive - 1996). Any RF noise
induced in the console frame(s) is directed to the “local” ZSRP, which is the metal-
work of the power supply units. In order to take full advantage of the “RF noise immu-
nity” capability of the CADAC system, PSU a.c. mains cables and the a.c. mains
supply EARTH conductor must be connected correctly.
FIG 1-2. AC mains grounding diagram (single phase 208-240V)
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