HowTo DIN-Rail earth connection

Author: CEmarking TEAM | Last edited: 09.05.2020

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.).

Which means:

permanently

The contact points are secured against loosening under mechanical stress and protected against oxidation/corrosion

highly conductive

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