HowTo DIN-Rail earth connection
This question is often raised by MCC manufacturers, electricians and OEM´s; and is the case, for example, when electrical components in a motor control cabinet are snapped onto DIN-rails, which are attached to a mounting plate.
Answers are provided by IEC 61439-1/-2 and IEC 60204-1; see clause 8.2.2 Protective conductors.
According to these standards, electrically conductive structural components are only permitted as part of the protective conductor connection if the basic requirements of a permanent, well-conductive and sufficiently current-carrying connection are met. If these are fulfilled, the mounting rail can be sufficiently connected to the protective earth conductor via its fastening with the large-area contact on a bare metal mounting plate, or also via the fastening means (mounting brackets, spacer bolts, etc.) when fastening to the enclosure system (frame, extension rails, etc.).
The contact points are secured against loosening under mechanical stress and protected against oxidation/corrosion
A measured resistance value between the contact of the component on the DIN-rail and the PE terminal of the incoming supply is < 0.1 Ohm
Sufficient current carrying capacity
Must match a corresponding copper conductor in contact surface and cross section