Siemens Automation System S7-400 - Manual (Page 206)

Guidelines for Handling Electrostatically-Sensitive Devices (ESD)
B-2
Automation System S7-400 Hardware and Installation
A5E00850741-01
B.1 What is ESD?
Definition:
All electronic modules are equipped with large-scale integrated ICs or components.
Due to their design, these electronic elements are very sensitive to overvoltages
and thus to any electrostatic discharge.
These Electrostatically-Sensitive Devices are commonly referred to by the
abbreviation ESD.
Electrostatically-sensitive devices are labeled with the following symbol:
!
Caution
Electrostatically-sensitive devices are subject to voltages that are far below the
voltage values that can still be perceived by human beings. These voltages are
present if you touch a component or the electrical connections of a module without
previously being electrostatically discharged. In most cases, the damage caused
by an overvoltage is not immediately noticeable and results in total damage only
after a prolonged period of operation.