Guidelines for Grounding and Earthing in the Cabinet

Guidelines for Grounding and Earthing in the Cabinet

Guidelines for Earthing and Grounding in the Cabinet The following guidelines should be observed when grounding a cabinet:  An unpainted earth reference plane or rail must be installed on the floor of the cabinet for the conventional reference potential.  All metal parts of the cabinet are connected with each other.  The metal housing of the cabinet must be integrated in the higher level earthing system.  All protective grounding conductors must be earthed.

Constructing earth and ground in the cabinet The following illustration shows how the earth and grounding system is constructed in the cabinet.

EB Adjacent cabinet or jig FE The functional earth, e.g. the iron beam of the hall, water or heating supply pipes, or neutral earthing for the hall

HS Mounting rail for installing the module backplane or the installation accessories M Reference conductor system or reference conductor rail (massive copper busbar or bridged terminal block) MA Grounding (earth reference plane or rail) that is used as the functional earth PE Protective earth PE, via protective earth choke

Guidelines for installing a ground connection in the cabinet In cabinets and machines, there are a lot of grounding structures which enable a maximum of protective effects. The following guidelines should be observed when installing a ground connection in a cabinet:  An unpainted earth reference plane or rail must be installed on the floor of the cabinet for the common reference potential.  The sheet or metal grid that acts as the earth reference plane or rail is connected to the cabinets metal housing at several points that is integrated with the systems ground connection.  All electrical components (filters etc.) are bolted directly to this earth reference plane or rail.  All cables are fixed straight through this earth reference plane/rail.  The all-around contact of the cable shield is created using locknuts that are bolted straight through the earth reference plane/rail.  All these electrical connections should be made with utmost care to achieve a low resistance connection.  Plastic cable ducts are permitted in enclosures if they are systematically mounted on the cage at the back or on DIN rails that are themselves connected to the grounds in the enclosure.  The design of enclosures means that many elements, including the doors, are only mounted at particular points (using screws, welding, hinges, etc). This results in several gaps. Entry and exit of cables must be systematically located near these mounting points or duplicated by a grounding braid. This layout means the gap can be masked and the protective effects thus maintained.  For a shielded cable connection (seepage116), it is advised to use a fixed cross-panel screen connection via metallic compression gland. This solution is better than any other solution, providing that the paint is scraped off in order to ensure a good electrical contact. However, a jumper can also be used, to ensure contact over at least 180°. NOTE: The way in which shielded cables are connected directly determines the HF protective effect. If the connection is made up using a "pigtail", that is, a single wire, protection is no longer provided at HF. Use of the "pigtail" is not recommended.