Best practices for minimizing electrical noise in electrical control panels

5. The real purpose of grounding is to provide an alternative path around the electrical system for lightning and other surges that cause dangerously high voltage levels that can damage equipment.

8. Bonding of devices maintains all metalwork at the same electrical potential. Bonding helps prevent this.

11. Why High Frequency Bonding? Drives and other electrically noisy devices can introduce common noise current. Good bonding techniques also meet the requirements for NEC. Diagram shows the potential paths for common mode noise and also shows that there is no low-impedance path for fault current. Return path is through ground. Faults could present dangerous levels of voltage and won’t necessarily cause circuit protection device to trip.

12. Ground Fault Current Path Effective Bonding With effective bonding in place, the voltage potential for all devices should be closer thus attenuating the common mode noise. Further, in the case of a fault, a low impedance path is in place that should provide protection.

14. Good Bond to Back Plane Paint must be removed at all mounting points. When the paint is removed some kind of conductive coating must be applied. If no conductive coating is applied over time oxidation will occur, resistance will build up, and noise will increase.

18. Segregation in the Panel Front view of a panel with components segregated into clean and dirty zones. The strip of clean duct in the center of the panel running parallel to the PWM drive is actually not a good idea.

19. Best Practice Segregation Best practice for panel building would be to move very dirty components onto a separate panel and bond that panel to the main back panel with braided straps.

20. Segregating Component Categories Top view of cabinet with panel segregated according to component categories.

22. Use of Shielded Drive Cable Shielded drive cable can attenuate common mode noise between the two ends of the drive cable by a factor of 1000:1 when the shield is bonded on both ends of the cable.

23. Use of Shield in Panel Use shielding in the cabinet any time zones cannot be physically separated.

25. Low-Pass Filters Low pass filters are inexpensive and can be used to reduce the coupling effect between cable runs. The effectiveness of an in-line filter is dependent on a good bond between the DIN Rail and the back plane.

26. Filtering between Zones In some instances it might be necessary to provide filtering between zones. Tests can be performed to determine if this is necessary and are described in detail in the manuals referenced.

28. AC Suppression Solutions for suppressing AC switching noise. Suppressors that are located across the contact provide the best clamping.

29. DC Suppression Solutions for suppressing DC switching noise. Once again, closer to the switch is better.

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