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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Safety guidelines 2019-05-15
The following regulations apply to the I/O modules:
Item
Regulations
Combination of
mains and low voltage
is admissible
With relay modules the safe distance of PCB tracks and
terminals is wide enough to make the combination of mains
and low voltage on the same module permissible.
Status contacts
• Digital inputs are not electrically isolated from the system
electronics.
– Mechanical contacts must be volt-free.
– Electronic switches must comply with SELV or PELV
standards.
• Voltage sensing is not supported.
Override buttons
The override buttons on the switching and positioning
outputs must not be used as safety isolators, e.g. for service
or maintenance purposes.
2.4.3 Connecting field devices to I/O modules
The voltage circuits of these devices must be adequately isolated from each other so
that they can be connected directly and without additional insulation (see the principles
diagram below).
Connections via interfaces may result in the distribution of dangerous voltages
throughout the building. Always ensure in such cases that the required insulation is
provided and that you have observed all the relevant installation regulations.
The following applies to low-voltage field devices and interfaces:
Item
Regulations
Field devices
connected to I/O
modules
Field devices such as sensors, status contacts and actuators
connected to the low-voltage inputs and outputs of I/O
modules must comply with the requirements for SELV or
PELV.
Low voltage
interfaces
The interfaces of field devices and other systems must also
satisfy SELV or PELV requirements.
I/O modules
Devices with different
voltage circuits
Interfaces between
different voltage circuits
SELV / PELV