How To Avoid Electrical Noise Problems; Emi / Rfi Interference - O. Thompson Microflite Ultra 2000 Installation & Adjustment Manual

The low level conductor, in the case of Ultra 2000, may be a 24 volt input that really only needs
to see 12 volts to turn on. If the voltage induced from the high power conductor is large enough
to induce a 12 volt spike, the input can falsely turn on.

4.1.2 How to Avoid Electrical Noise Problems

Noise problems can be avoided in a variety of ways. The easiest way to avoid noise problems is
in the proper routing of high and low level signal wiring. Keep low level wiring in separate conduit
from high power wiring. The separate conduit provides a shield from electrical noise. If high and
low power wiring must be run in the same duct, try to keep them a minimum of three to four inches
apart. Also, if the two must cross each other, they should cross at a ninety degree angle to each
other. Sometimes this is not practical.
A second way of protecting against electrical noise problems is to run low level wiring in shielded
cable. It is very expensive to run all wiring in this manner, so only certain signals are run in this
manner. The shield provides a conductor external to the actual signal wiring to collect any induced
voltage from surrounding high power wiring.
The shield or "drain", as it is often referred to, is then connected to ground on one end. With the
induced voltage connected directly to ground, the induced spike is suppressed immediately before
affecting the actual signal being shielded. The shield or "drain" should never be connected to
ground at both ends.
4.1.3 Possible EMI / RFI Interference
Many papers concerning recommended wiring practices have been written on EMI (Electro
Magnetic Interference) and RFI (Radio Frequency Interference). The main sources of these types
of problems are semiconductor devices that switch at high base frequencies such as variable
frequency drives. The most common method of eliminating these types of problems is through
proper power cable piping and routing and proper grounding. The following wiring practices
should be followed when piping and wiring high voltage lines to avoid EMI problems:
Run all motor leads in a separate conduit all the way back to the control cabinet. All motor
1.
lead runs should be as short as possible and the entry into the control cabinet should be
as close to the final termination point in the cabinet as possible.
2. Run main line supply leads in a separate conduit all the way back to the control cabinet.
3. Run all primary isolation transformer wiring in separate conduit from the main line to the
transformer. (SCR Drives Only)
4. Run all secondary isolation transformer wiring in a separate conduit from the transformer
to the drive cabinet. (SCR Drives Only)
5. A SINGLE POINT GROUND should be established inside the control cabinet and a #8
AWG ground wire should be run direct from each of the following devices to this one single
point:
A) Earth Ground from running water supply, hydro-electric supplied ground, or a
ground supplied via an earthing rod to the single ground stud.
B) Continuous wire from the main line disconnect to the single ground stud.
C) Continuous wire from the motor frame to the single ground stud.
Revision: AA 2.2
Microflite Ultra 2000
Printed 03 - 15 - 03 4 - 2