MIC 1400 Manual
Edition 1
11
2.2.1.5 NOISE SUPPRESSION AT THE SOURCE
Usually when good wiring practices are followed no further noise protection
is necessary. Sometimes in severe electrical environments, the amount of
noise is so great that it has to be suppressed at the source. Many manu-
facturers of relays, contactors, etc. supply “surge suppressors” which
mount on the noise source.
For those devices that do not have surge suppressors supplied, RC (resis-
tance-capacitance) networks and/or MOV (metal oxide varistors) may be
added.
Inductive Coils - MOV’s are recommended for transient suppression in
inductive coils connected in parallel and as close as possible to the coil.
See Figure 2-4. Additional protection may be provided by adding an RC
network across the MOV.
FIGURE 2-4
Contacts - Arcing may occur across contacts when the contact opens and
closes. This results in electrical noise as well as damage to the contacts.
Connecting a RC network properly sized can eliminate this arc.
For circuits up to 3 amps, a combination of a 47 ohm resistor and 0.1
microfarad capacitor (1000 volts) is recommended. For circuits from 3 to 5
amps, connect 2 of these in parallel. See Figure 2-5, page 12.
0.5
mfd
1000V
220
ohms
Coil
115V 1/4W
230V 1W
