Power and Grounding - Best Practices
Download as PPTX, PDF3 likes3,397 views
![rAVe [PUBS] , profile picture](https://cdn.slidesharecdn.com/profile-photo-ravepubs-48x48.jpg?cb=1555444376)
The document presents a discussion on best practices for power and grounding systems in audiovisual systems, led by Tom Kehr, an experienced professional in the field. Key topics include system and equipment grounding, ground faults, noise defense strategies, and the importance of specifying proper circuits and grounding techniques. The document emphasizes the safety and effectiveness of audio systems through correctly implemented grounding practices.
Power and Grounding - Best Practices
- 2. Presenter • Tom Kehr, CTS-D, CTS-I, ISF-C, LEED Green Associate, Network+ • Since 1986, Tom has been involved in either designing, installing, operating or purchasing audiovisual systems. • Tom has also been heavily involved in church audio, leading ministry teams and training volunteers in both permanent and portable venues. In addition, he owned a regional sound reinforcement company for over 16 years. • Prior to joining InfoComm, Tom was a senior designer for a large Washington, D.C. area firm. He is a member of Syn-Aud-Con and AES and is a licensed amateur radio operator.
- 3. Agenda • To recognize best practices for power and grounding systems for AV systems • To be able to discuss why these are best practices
- 4. Outline • Current pathways • System Grounding • Equipment Grounding • Ground Faults • Rack Grounding • What to specify • Ground Loops • Noise Defense
- 5. Authority Having Jurisdiction • Enforces codes and regulations (Required) • We can also apply: – Standards • Industry • Client – Best Practices
- 6. Avoid Ambiguous Terms • Dedicated power • Dedicated ground • Clean power • Dirty power • Quiet ground • Low or high voltage • Technical power • Technical ground
- 7. Use Electrician (NEC) Terms • Panelboard • Individual branch circuit • Auxiliary Ground • Isolated Ground
- 8. Panelboard • Main service panelboard • Sub-panelboard
- 9. Circuit Theory • Electricity seeks to go to ground
- 10. Circuit Theory • “Electrical current is the unseen movement of electrons that flow from the power source through the electrical circuit of the appliance or equipment and then return to the power source. The complete path the electrons take is called the electrical circuit.” – Mike Holt, “Basic Electrical Theory”
- 13. Circuit Theory • All of the electrons leaving the source of power go through each component in the circuit and return to the source
- 14. Electricity Goes To Ground? • Let’s explore
- 15. Complete The Circuit • Why have ground?
- 16. Circuit Theory • Electricity always takes the path of least resistance
- 17. Circuit Theory • While more current will flow through the path of lesser resistance, current will take any and all available pathways • Path could be an unintentional path – Safety 100,000Ω 1,000Ω 10Ω I = V / R 1.2 mA = 120 / 100,000 120 mA = 120 / 1,000 12 A = 120 / 10
- 18. System Grounding • The Grounded Conductor is frequently the Neutral and it is the return path back to the electrical source
- 19. Lightning/Surges On Power Line
- 20. System Grounding • Lightning, line surges and unintentional contact with higher voltage lines • Reduce fires • Protects the electrical system
- 21. Equipment Grounding • NEC: Non-current-carrying conductive materials … shall be connected to earth
- 22. Ground Fault • Current path during a ground-fault • Connection to earth is not involved
- 23. Ground Fault • Interruption of Ground-Fault Current Path – Improper use of Grounding Adapter • Not a “Ground Lift Adapter” – Not to be used to solve hum and buzz problems
- 24. Circuit Theory • While the majority of the current will flow through the path of lesser resistance, current will take any and all available pathways • Path could be an unintentional path – Safety 100,000Ω 1,000Ω 10Ω I = V / R 1.2 mA = 120 / 100,000 120 mA = 120 / 1,000 12 A = 120 / 10
- 25. • Common ground stud for all gear Grounding Racks
- 26. Grounding Racks
- 27. Grounding Racks
- 28. Grounding Racks
- 29. Review - • Current seeks to return to the source • It will take any and all pathways • System Grounding – One of the current carrying conductors • Equipment Grounding – Non-current carrying conductive materials • Current pathway for a Ground Fault – Do not use Grounding Adapters • Proper Rack Grounding
- 30. Auxiliary Ground • Auxiliary Equipment Grounding Conductor – Insures low impedance equipment ground – Avoids depending upon conduit installation
- 31. Auxiliary vs. Isolated Ground
- 32. Specify - • Branch circuits for “Audiovisual Use Only” with auxiliary equipment grounding conductor
- 33. Ground Loops • A ground loop is a continuous conductive loop – Formed by using the Equipment Grounding (safety) Conductors of any two electronic devices and the cable shield connecting those two devices – Formed by the shields of two interconnecting cables between any two electronic devices – Normal, common – Not always problematic
- 34. Ground Loops
- 35. Ground Loops
- 36. Noise Defense - Shielding • Shield –Metallic partition –Works bidirectionally • Contains • Keeps out –50 / 60 Hz –Nearfield
- 37. Noise Defense - Shielding • Magnetic Fields – Uses any magnetically permeable material to absorb and conduct magnetic lines of flux • Magnetically permeable materials include: – Iron, steel, nickel alloys • Iron, steel, nickel alloys vary in their permeability – “Permeability” – Ability to conduct magnetic fields
- 38. Noise Defense - Shielding • Electric Fields – Uses any electrically conductive material to absorb and conduct electrical lines of force • Electrically conductive materials include: – Gold, silver, copper, aluminum, etc. • Gold, silver, copper, aluminum, etc. vary in their conductivity – “Conductivity” – Ability to conduct an electrical current – Conductivity is the opposite of resistance
- 39. Shielding
- 40. Shielding
- 41. Noise Defense • Balanced Interfaces • CMR Specifications – Lab measurement vs. “real world” – Component tolerances create slight impedance imbalances – CMR specifications should be in accordance with IEC Standard 60268-3
- 42. Noise Defense Differential-Mode Signal Common-Mode Noise Common-Mode Noise with Differential-Mode Signal
- 43. Review - • Specify – Individual branch circuits with auxiliary equipment grounding conductors • Ground loops – Normal, expected – Not all are problematic • Noise Defense – Shielding - What works and what doesn’t at 60 Hz – Specify steel conduit – Use balanced interfaces with quantifiable CMRR specifications
- 44. What We Have Covered: • Current pathways • System Grounding • Equipment Grounding • Ground Faults • Rack Grounding • What to specify • Ground Loops • Noise Defense
- 45. Questions?