Siemens Simatic S7-400 - Manual (Page 602)

Guidelines for Handling Electrostatic Sensitive Devices (ESD)
D-4
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
D.3 General Protective Measures Against Electrostatic
Discharge Damage
Ensure Sufficient Grounding
Make sure that the personnel, working surfaces and packaging are sufficiently
grounded when handling electrostatic sensitive devices. You thus avoid
electrostatic charging.
Avoid Direct Contact
You should touch electrostatic sensitive devices only if it is unavoidable
(for example, during maintenance work). Hold modules without touching the pins of
components or printed conductors. In this way, the discharged energy cannot affect
the sensitive devices.
If you have to carry out measurements on a module, you must discharge your body
before you start the measurement by touching grounded metallic parts. Use
grounded measuring devices only.