1/01 UDC3300 Limit Controller Product Manual 101
9.6 Noise Suppression at the Source
Introduction
Generally speaking, when good wiring practices are used with well-
designed digital electronic equipment, no further noise protection is
necessary. However, in some severe electrical environments, the
magnitude of the electrical noise is so great that it must be suppressed at
the source. In most control cabinets, the main sources of noise are motor
starters, contactors, relays, and switching gear. For this reason, many
manufacturers of these devices supply “surge suppressors” which mount
directly on the noise source, (for example, on the coil of a control relay or
motor starter).
For those devices that do not have accessory “surge suppressors,”
resistance-capacitance (RC) circuits and/or voltage limiters such as metal
varistors may be added when and where needed. This can be broken down
into two categories, namely inductive loads (for example, a relay switch
in series with a relay coil) and contacts.
Inductive coils
Metal Oxide Varistors (MOVs) are recommended for transient
suppression in inductive coils. An MOV is connected in parallel with the
coil and is as close as physically possible to the coil (see Figure 9-2).
MOV devices (listed in Table 9-2) are recommended for general purpose
applications.
Table 9-2 lists part numbers for recommended MOV devices.
Table 9-2 MOV Devices
Part Number 30732481-001 30732481-002
Maximum AC 130V 275V
Energy Pulse Rating 10 Joules 15 Joules
Supplier (General Electric) V130LA10A V275LA15A
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