Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 24)

Chapter 1
Installing Your Controller
1–8
Suitable surge suppression methods for inductive ac load devices include a
varistor, an RC network, or an Allen-Bradley surge suppressor, all shown
below. These components must be appropriately rated to suppress the
switching transient characteristic of the particular inductive device. See the
table on page 1–9 for recommended suppressors.
Output Device
Varistor
Output Device Output Device Output Device
RC Network
Surge
Suppressor
Surge Suppression for Inductive ac Load Devices
If you connect a micro controller triac output to control an inductive load, we
recommend that you use varistors to suppress noise. Choose a varistor that is
appropriate for the application. The suppressors we recommend for triac
outputs when switching 120V ac inductive loads are a Harris MOV, part
number V175 LA10A, or an Allen-Bradley MOV, catalog number 599-K04
or 599-KA04. Consult the varistor manufacturer’s data sheet when selecting
a varistor for your application.
For inductive dc load devices, a diode is suitable. A 1N4004 diode is
acceptable for most applications. A surge suppressor can also be used. See
the table on page 1–9 for recommended suppressors.
As shown in the illustration below, these surge suppression circuits connect
directly across the load device. This reduces arcing of the output contacts.
(High transient can cause arcing that occurs when switching off an inductive
device.)
Output Device Output Device
Diode
(A surge suppressor can also be used.)
— +
Surge Suppression for Inductive dc Load Devices