Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 29)

Publication GMC-RM001A-EN-P — July 2001
High Frequency (HF) Bonding 2-11
Machine Structure
If the machine structure covers a large portion of the system area and
is constructed of a conductive material with all sections closely
bonded, then it too will form an excellent ground plane. Care should
be taken to ensure paint is removed at the bonds and the connections
protected against corrosion.
Figure 2.9
Panel ground plane extended to the machine structure
Bond the panel(s) to the machine structure as tight as possible, but if
this proves difficult, construct a low impedance path using the
following guidelines:
• Use a zinc-plated tray, as wide as practical, and join sections by
overlapping with several fasteners across the width. The
perforations will not reduce performance (refer to Figure 2.10).
• EMC trunking (plated at joint surfaces with conductive gaskets)
also makes a good bond.
• Short and wide is the requirement for any HF bonding material.
Panel(s) should be located as close to the machine structure as
practical and the bond should be firmly attached at both the
machine structure and the control panel (not the cabinet outer
panels).
• Multiple trays/trunking are better.
Note that copper wire safety earth bonding is still required. Refer to
the section Grounding (Safety Earth) at the end of this chapter for
more information.
Panel ground plane
bonded to structure ground plane by
clean and dirty wireways
Machine structure used as ground plane