• Generally, the fewer and smaller the holes in the cabinet, the better the interference
attenuation. The maximum recommended diameter of a hole in galvanic metal contact
in the covering cabinet structure is 100 mm (3.94 in). Pay special attention to the cooling
air inlet and outlet gratings.
• The best galvanic connection between the steel panels is achieved by welding them
together as no holes are necessary. If welding is not possible, ABB recommends to leave
the seams between the panels unpainted and equipped with special conductive EMC
strips to provide adequate galvanic connection. Usually, reliable strips are made of flexible
silicon mass covered with a metal mesh. The non-tightened touch-contact of the metal
surfaces is not sufficient, so a conductive gasket between the surfaces is required. The
maximum recommended distance between assembly screws is 100 mm (3.94 in).
• Construct sufficient high-frequency grounding network in the cabinet to avoid voltage
differences and forming of high-impedance radiator structures. A good high-frequency
grounding is made with short flat copper braids for low inductance. One-point
high-frequency grounding cannot be used due to the long distances inside the cabinet.
• 360° high-frequency grounding of the cable shields at the cable entries improves the
EMC shielding of the cabinet.
• ABB recommends 360° high-frequency grounding of the motor cable shields at their
entries. The grounding can be implemented by a knitted wire mesh screening as shown
below.
Cable1
Cable tie2
Strain relief3
Bare cable shield4
Knitted wire mesh5
Cabinet entry plate6
Generic cabinet planning instructions 47
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