Installation Instructions

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Siemens Desigo Desigo Room automation - Engineering, mounting and installation CM111043en_14
Smart Infrastructure Important information on safety 2020-10-30
Observe the following points when grounding ^ AC 24 V (system neutral):
· As a principle, operating voltage of AC 24 V is permitted in principle for both
grounded (PELV) as well as non-grounded (SELV) system neutral. Local
regulations and customers apply accordingly.
Grounding may be required or not allowed for functional reasons.
· Recommendation: PELV installation. AC 24 V systems are grounded unless
disadvised by any of the field device manufacturers.
· System neutral ꓕ must be grounded at a single point at the primary transformer.
· Where AC 24V power for field devices is not distributed by the TX-I/O terminals,
all secondary transformers powering the field devices must be star grounded to
the single point at the primary transformer.
· Caution: where AC 24V system neutral ꓕ is not grounded, all connected de-
vices using ꓕ must be capable of accepting AC 24V on their ꓕ terminal.
This means they must be SELV-compatible.
· Caution: where AC 24V system neutral ꓕ is not grounded, USB must be
isolated from laptop using an USB isolator.
· In order to avoid ground loops, connect systems with PELV to the ground at one
location only (especially for transformers), if no other indication exists.
· AC 230 V devices and AC 230 V field devices must not be grounded.
Mains and operating voltage
Operating voltage AC 24 V It must meet requirements for SELV or PELV. Permitted deviation for nominal
voltage
· At the transformer: AC 24 V -10 - + 20%.
· At the room automation station: AC 24 V -12 - + 20%.
· At the field devices: AC 24 V -20 - + 20%.
Do not interchange the conductors V~ and ^ (system neutral), otherwise island
bus and USB communications will not work properly.
Transformer specification
AC 24 V
· IEC: Use safety insulating transformers as per IEC 61558 with double
insulation designed for 100% duty to supply SELV or PELV circuits.
· USA: Class 2 circuits to UL 5085-3.
· Power taken from the transformer should be at least 50% of nominal load for
efficiency reasons (effectiveness).
· Transformer nominal power should be at least 25 VA. For smaller transformers,
the ratio of open circuit voltage to full load is unfavorable
(> + 20%).
Operational voltage fuse
AC 24 V
Transformers on the secondary side correspond to the actual load of all
connected devices as per transformer sizing:
· AC 24 V line (system potential) must always be fused.
· Where required, also line ^ (system neutral).
Mains fuse Transformer, primary side:
Installation box fuse (control circuit fuse).
Operating voltage
AC 230 V
For devices with AC 230 V supply:
· The sizing and fuse protection of the supply cables depends on the total load
and on local regulations.
· Supply cables must be secured with cable restraints on the room automation
station.
Grounding of
^
(System neutral AC 24 V
)
Grounding of
AC 230 V