16 UNT Controller—Unitary Controller (UNT)
The standard UNT, when powered by any typical separate isolation
transformer or stepdown transformer, operates reliably in an electrical
environment defined as Location Category A by the IEEE 587 Standard;
that is, when installed more than 30 feet from electrical distribution
panels or major bus and feeder systems in industrial plants.
IEEE 587 Location Category A power line surge/noise level is specified at
6 kV, 500 A (Normal Mode Ringwave).
The UNT exceeds the Category A specification by meeting these surge
levels as well:
IEEE-587 style Common Mode Pulse 3 kV
IEEE-587 style Normal Mode Pulse 1.5 kV
IEEE-472 style Common Mode Ringwave 1.5 kV
IEEE-472 style Normal Mode Ringwave 500 V
When the controller is installed within 9 m (30 ft) of electrical distribution
panels or major bus and feeder systems in industrial plants, you must take
further precautions to prevent unwanted binary output cycling, resetting,
or other possible controller malfunctions. This electrical environment is
defined as Location Category B by the IEEE 587 Standard.
You can use the following method to prevent electrical noise from
adversely affecting the controller:
•
Connect an MOV (Metal Oxide Varistor) across the UNT supply
transformer primary. The MOV must be rated appropriately for the
line voltage. Use the list in Table 4 to select the correct MOV sold
through your electronics parts distributor.
The UNT meets the following power line surge/noise standards when you
correctly apply the MOV as described.
IEEE-587 Common Mode Pulse 1.5 kV
Normal Mode Pulse 6 kV
Normal Mode Ringwave 6 kV
IEEE-472 Common Mode Ringwave 1.5 kV
Normal Mode Ringwave 500 V
Note: The 50 VA split bobbin transformer in the EWC15 or -101 model
UNT provides additional surge/noise immunity.
For more information, refer to Appendix A: Precautions for Rooftop
Installations in this technical bulletin.
Power Line
Wiring
Transient Noise
Precautions
Surge Levels
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