Recognize best practices for power and grounding systems for AV systems. Be able to discuss why these are the best practices.

1. Power and Grounding

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”

11. Electrical Circuit

12. Electrical Circuit

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?