Rockwell Automation 1770 Industrial Automation Wiring and Grounding Guidelines - Manual (Page 18)

Industrial Automation Wiring and Grounding Guidelines 18
Publication 1770-4.1 – February 1998
Surge-suppressors are usually most effective when connected at the
inductive loads. They are still usable when connected at the
switching devices; however, this may be less effective because the
wires connecting the switching devices to the inductive loads act as
antennas that radiate emi. You can see the effectiveness of a
particular suppressor by using an oscilloscope to observe the voltage
waveform on the line.
Ferrite beads can provide additional suppression of transient emi.
Fair-Rite Products Corporation manufactures a ferrite bead (part
number 2643626502) which can be slipped over category-2 and -3
conductors. You can secure them with heat-shrink tubing or
tie-wraps. With a ferrite bead located near the end of a cable (or
cable segment in the case of a daisy-chain or dropline configuration)
transient emi induced onto the cable can be suppressed by the bead
before it enters the equipment connected to the end of the cable.
Fluorescent lamps are also sources of emi. If you must use
fluorescent lamps inside an enclosure, the following precautions may
help guard against emi problems from this source as shown in
Figure 12:
•
install a shielding grid over the lamp
•
use shielded cable between the lamp and its switch
•
use a metal-encased switch
•
install a filter between the switch and the power line, or shield the
power-line cable
Figure 12
Installation Requirements for Suppressing Noise from
Fluorescent Lamps Inside an Enclosure
12619-I
Filter
Shielding-grid
over lamp Shielded
cable Metel-encased
switch Line-filter or
shielded
power line
ac power
Ferrite Beads
Enclosure Lighting