User Manual

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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Safety guidelines 2019-05-15
Fuses to protect
AC 24 V operating
voltage
Important
Transformers, secondary winding: based on the
effective
load of all connected devices in accordance with the
transformer sizing
:
• The AC 24 V conductor (system potential) must always be
fused
• Where specified, an additional fuse must be provided for the
reference conductor ⊥ (system neutral).
• The 10 A fine-wire fuses fitted to the power supply units to
protect the I/O island are not a substitute for the load-
dependent back-up fuse.
Refer to Section10.9.
The introduction of hazardous voltages into the low voltage circuits of the system (e.g.
due to faulty wiring or to parasitic voltages in the TX-I/O modules) represents an
immediate danger to personal safety and may cause irreparable damage to the building
automation and control system.
• Adhere to local regulations on lighting protection and equipotential bonding.
• Overvoltage protection devices can falsify the measured value of analog inputs.
Example: Phoenix type PT 1X2-12DC-ST/28 56 02 9 has an internal protective impe-
dance which causes a measuring error of +1K, but only for LG-Ni 1000 sensors.
• Adhere to local regulations on Explosion protection.
• Explosion protection devices can falsify the measured value of analog inputs.
Example: Pepperl & Fuchs type CFD2-RR-Ex19 causes considerable measuring
errors for resistance values of <30 ohms. Resistances >30 ohms are measured
correctly.
Transformer sizing
Beware of external
voltages!
Overvoltage
protection
Explosion
protection