Rockwell Automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE - Manual (Page 126)

5-2 SMC Dialog Plus Controller Special Application Considerations
Use of Protective Modules
(cont.) There are two general situations that may occur which would indicate
the need for utilizing the protective modules.
1. Transient spikes may occur on the lines feeding the SMC Dialog
Plus controller (or feeding the load from the SMC Dialog Plus
controller). Lightning can cause spikes. Spikes are also created
on the line when devices are attached with current-carrying
inductances that are open-circuited. The energy stored in the
magnetic field is released when the contacts open the circuit.
Examples of these are lightly loaded motors, transformers,
solenoids, and electromechanical brakes.
2. The second situation arises when the SMC Dialog Plus controller
is installed on a system which has fast-rising wavefronts present,
although not necessarily high peak voltages. Lightning strikes
can cause this type of response. Additionally, if the SMC Dialog
Plus controller is on the same bus as other SCR devices, (AC/DC
drives, induction heating equipment, or welding equipment) th
firing of the SCRs in those devices can cause noise. This high
frequency noise can penetrate the SMC Dialog Plus controlle
through stray capacitance.
!
ATTENTION: When installing or inspecting the
protective module, disconnect the controller from th
power source. The protective module should be
checked periodically. Inspect for damage or
discoloration. Replace if necessary.