42 en | Installation wiring PRAESENSA
2021.12.21 | V0.15b | F.01U.402.882
Underwriters Laboratories Listing Document (ULLD)
Bosch Security Systems B.V.
Single Class A wiring (A to B)
Figure3.5: Single Class A wiring
A third loudspeaker connection topology is the so-called Class‑A loop, where the loudspeakers
are connected in a loop, starting at output A and ending at output B, with the end of the loop
being supervised with an end‑of‑line device.
Follow the procedure below to connect the loudspeakers according to this scheme.
1. Connect all loudspeaker in parallel in a loop‑through fashion. Observe equal polarity for
all loudspeakers. Connect one side of the loudspeaker cable to output A, observing
polarity.
2. Connect the other side of the loudspeaker cable to output B. In this case maintaining the
correct polarity is especially important, as reversal on one end will short circuit the
amplifier channel, not immediately, but when output B is activated in case of interruption
of one conductor.
3. Connect an end-of-line device to the end-of-line connection terminals. These terminals are
connected in parallel to output B, internally in the amplifier, to include supervision of the
output B connection.
Output fault detection
Output fault detection can be tested with the following means:
– Ground short detection: Connect between one of the output conductors, of one of the
loudspeaker outputs and safety ground, a 50kohm resistor.
– Short circuit: Connect a ≤500mohm resistor between the plus and minus of output A or
output B, of one of the loudspeaker outputs.
– Open circuit: Unplug one of the loudspeaker output connectors.
Refer to
– Field wire cable requirements, page 19
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