EMC implementation - Cabinet cabling

From Electrical Installation Guide
Home > ElectroMagnetic Compatibility (EMC) > EMC implementation > EMC implementation - Cabinet cabling

(See Fig. R22)

Each cabinet must be equipped with an earthing bar or a ground reference metal sheet. All shielded cables and external protection circuits must be connected to this point. Anyone of the cabinet metal sheets or the DIN rail can be used as the ground reference.

Plastic cabinets are not recommended. In this case, the DIN rail must be used as ground reference.

Fig. R22 – Grounding and bonding examples

Cabinet cabling recommendations

Each cabinet, cubicle or enclosure shall be fitted, as a minimum, with an earthing bar and a reference metallic plate or grid (grounding plate). All the metallic parts (frames, panels, roof, door, etc.) shall be interconnected together with adapted features.

The use of specific washer is recommended. Some examples of preferred ones are shown below:

Fig. R23 – Preferred washers examples
Fig. R24 – Some examples of washers, bolt and lugs mounting.
Fig. R25 – Earthing and bonding examples

All the cables shall be laid on the grounded/earthed metallic structures.

All EMC components (e.g. EMI filter, EMC clamps) shall be fixed directly on the metallic plates without any insulating coating (e.g. free of paint or varnish).

Screened cables coming or going out from the cubicle shall be bonded to the earthing bar or grounding plate if these cables are coming from long distance and/or from non equipotential zones.

The goal is to divert the disturbing currents at the cabinet entrance and not inside the cabinet.

Non metallic cabinet are not recommended for EMC purposes.

To protect electronics equipment against low frequency magnetic field, it is recommended to use (galvanized) steel cabinets.

Non magnetic metals (e.g. aluminum, stainless steel) are more efficient for high frequencies environment.

Power and low level apparatus shall be physically separated and cables segregation and distances between power and sensitive cables shall also be respected as shown on the figures below

Fig. R26 – Correct EMC design inside a same cabinet
Fig. R27 – Correct EMC design inside two separate cabinets