Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 31)

Publication GMC-RM001A-EN-P — July 2001
High Frequency (HF) Bonding 2-13
Existing Buildings
The nearest building steel structures between the machine and control
cabinets may be used to bond to.
If there is more than 20 m (65 ft) between the building structural steel
closest to the motor and the building structural steel closest to the
control panel, the ground between these two structural points should
be checked and enhanced, if necessary, using at least 25 mm (1 in.)
wide wire braid.
Limits
A ground plane sub-panel may only be considered part of a larger
ground plane when bonded sufficiently well at RF. For this purpose
wide thin strips are more effective than wire. Refer to the section
Bonding Surfaces in Appendix A for more information.
• Length
≤
width x 10 is the generally accepted maximum ratio.
• Shorter = better
• Wider = better
• Thickness is not an issue. Thin is acceptable (even foil is very
effective, but fragile).
The building example shown in Figure 2.11 normally falls outside
these requirements.
In cases where the maximum 10:1 bonding aspect ratio limit cannot
be satisfied, a differential noise voltage must be assumed to exist
between each semi-isolated ground plane. All wiring entering a
ground plane will carry this noise voltage and must be dealt with at
the point of entry.
A ground plane is just as effective if it is perforated or made up of a
matrix of flat conductors, provided that the apertures are smaller than
one quarter of the wavelength of the highest troublesome frequency.