DL06 Micro PLC User Manual, 3rd Edition, Rev. E
Chapter 2: Installation, Wiring, and Specifications
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AC Coils:
Two options for AC coils are MOVs or bi-directional TVS diodes. These devices are most
effective at protecting the driver from a transient voltage when connected across the driver
(PLC output) but are also commonly connected across the coil. The optimum voltage rating
for the suppressor is the lowest rated voltage available that will NOT conduct at the supply
voltage, while allowing a safe margin.
AutomationDirect’s ZL-TSD8-120 transorb module is a good choice for 120VAC circuits.
It is a bank of eight bi-directional 180V TVS diodes.
ZL-TSD8-120
Transorb Module
NOTE: Manufacturers of devices with coils frequently offer MOV or TVS diode suppressors as an add-
on option which mount conveniently across the coil. Before using them, carefully check the suppressor
ratings. Just because the suppressor is made specifically for that part does not mean it will reduce the
transient voltages to an acceptable level.
For example, a MOV or TVS diode rated for use on 24–48 VDC coils would need to have
a high enough voltage rating to NOT conduct at 48V. That suppressor might typically start
conducting at roughly 60VDC. If it were mounted across a 24V coil, transients of roughly
84V (if sinking output) or -60V (if sourcing output) could reach the PLC output. Many
semiconductor PLC outputs cannot tolerate such levels.
VAC
AC MOV or Bi-Directional Diode Circuit
