Connecting all metal parts together and to the system winding to provide a low-impedance path to the source to facilitate the opening of the circuit-protection device to remove dangerous voltages on metal parts.
Maintaining all metalwork at the same electrical potential. If different potentials exist the voltage difference is seen as common-mode noise on all interconnect wiring internal and external to the cabinet.
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.
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.
Back plane rather than ground bus/bar (back plane maintains a uniform potential at higher frequencies)
Paint must be removed at every mounting point and conductive coating reapplied
Minimal wire lengths and each ground wire on its own stud
Effective Bonding in the Panel The backplane provides a near perfect ground plane. All equipment properly bonded to it will be at the same voltage at all frequencies. Component ground conductors should be kept to a minimum length and each connection should be on its own stud. See example in following slide.
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.
Drives and Amplifiers, DC Bus, Ultrasonic Transducers, Contactors to Motors
Switch-mode DC Power Supply, Contactors, Lamps, Limit/Proximity Switches, Solenoids
Controllers, Communication Devices, Analog Devices, Encoder/Resolver Feedback Cables
Component Categories Separate the panel layout and cable runs into different categories depending on how noisy the components are.
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.
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.
Segregating Component Categories Top view of cabinet with panel segregated according to component categories.
Use low-pass filters to attenuate RF noise on cable runs.
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.
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.