Bosch PRAESENSA Installation Manual page 39

PRAESENSA
PRA-ES8P2S
This Ethernet switch has dual redundant 24 to 48 V DC-inputs. In case no battery backup is
required, it can be powered from a PRA-PSM24 or PRA-PSM48 power supply. In case the
switch is used in a Voice Alarm system, compliant to EN54‑16, the switch must be powered
from an EN54‑4 certified power supply, like the PRA-MPS3.
When the switch is powered by the PRA-MPS3 multifunction power supply, it must be
connected to one of the 48 V outputs, normally intended for the amplifiers. Use both A and B
outputs for connection redundancy. The 24 V output of the PRA-MPS3 is not powerful enough
for this switch. The 48 V output that is powering the switch should not be used to also power
an amplifier. Especially when the switch is serving multiple PoE powered devices as PSE
(Power Sourcing Equipment), its power consumption can raise to 140 W. The remaining
power capacity of the 48 V supply is not sufficient anymore for an amplifier under various load
conditions.
The lifeline that belongs to the powering 48 V output is not used, so the 48 V output will not
be disabled as would be for amplifiers in sleep/snooze mode to save power. It is also essential
that the 48 V for the switch is not disabled at any time. In case of mains failure the switch will
be powered from the battery, connected to the multifunction power supply.
The power consumption of the switch is highly dependent on the number of ports that are in
use and whether these ports provide PoE power to connected devices. Next to the power
consumption of the switch itself and the power consumption of the active ports, the PoE
loads of all ports together (expressed in watt) multiplied by 0.1 gives the approximate
additional load of the battery (expressed in ampere). Please note that a call station that is
connected to this switch and powered via PoE from this switch will load the battery slightly
more than when the same call station would have been directly powered from a PoE port of
the PRA-MPS3, because the switch in between has some 20% additional losses.
PRA-MPS3
The power consumption of the PRA-MPS3 itself is mainly determined by its network interface
and the number of active Ethernet ports (RJ45 or SFP). For the battery capacity calculation,
the power loss of the DC/DC converters to supply power to all connected devices is already
taken into account in the power taken from the battery by these devices. The power
consumption of the relays of the control outputs is insignificant.
Bosch Security Systems B.V. Installation manual
System composition | en
2019.11 | V1.00 |
39