minimizing electrical noise in panels

Best Practices in

Panel Building for

Minimizing Electrical Noise

Best Practices in

Panel Building for

Minimizing Electrical Noise

The focus of this presentation is on how to minimize electrical noise in the control system and the techniques used in panel building to minimize electrical noise.

What is Grounding?

According to NEC

Connecting to the earth or to some conducting body that serves in place of the earth.

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.

What is Bonding?

According to NEC

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.

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

• High Frequency Bonding• Segregation• Shielding• Filtering• Contact Suppression / Clamping

These are the five considerations for reducing electrical noise in a panel.

• High Frequency Bonding• Segregation• Shielding• Filtering• Contact Suppression / Clamping

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 PlanePaint 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.

• High Frequency Bonding• Segregation• Shielding• Filtering• Contact Suppression / Clamping

Separating sources and victims of electrical noise into zones. Noise coupling reduces with the square of separation distance.

• Very Dirty – Drives and Amplifiers, DC Bus, Ultrasonic

Transducers, Contactors to Motors

• Dirty – Switch-mode DC Power Supply, Contactors,

Lamps, Limit/Proximity Switches, Solenoids

• Clean – Controllers, Communication Devices, Analog

Devices, Encoder/Resolver Feedback Cables

Component Categories

• Very Dirty – Drives and Amplifiers, DC Bus, Ultrasonic

Transducers, Contactors to Motors

• Dirty – Switch-mode DC Power Supply, Contactors,

Lamps, Limit/Proximity Switches, Solenoids

• Clean – 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.

• High Frequency Bonding• Segregation• Shielding• Filtering• Contact Suppression / Clamping

Using shielded cable and steel barriers to reduce electrical noise when possible and cost effective and when devices in the cabinet cannot be separated by a sufficient distance (~6 inches).

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.

Use of Shield in Panel

Use shielding in the cabinet any time zones cannot be physically separated.

• High Frequency Bonding• Segregation• Shielding• Filtering• Contact Suppression / Clamping

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 ZonesIn 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.

• High Frequency Bonding• Segregation• Shielding• Filtering• Contact Suppression / Clamping

Adding contact suppression to switches is an easy and inexpensive way to reduce noise and is recommended for all applications.

AC Suppression

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

DC Suppression

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

Wiring and Grounding Guidelines for PulseWidth Modulated (PWM) AC Drives

Rockwell Automation Publication Number Drives-IN001_-EN-P

Reference Manuals

System Design for Control of Electrical NoiseRockwell Automation Publication Number

GMC-RM001A-EN-P

Reference Manuals

Effective grounding and bonding can minimize electrical noise issues

Best Practices for Panel Building include the use of:

•HF Bonding Techniques•Segregation of Component Categories•Proper Shielding•Filtering•Clamping and Contact Suppression

Thanks for Watching