CEDIA Home Technology Event 2011: Designing the Perfect Rack

Designing and Building The
Perfect Rack

Carl Ambrus
BEng(Hons) CCOI CCP CCPD HCDS THXII DMC-E MIET
European Design Manager & Acting Operations Manager

T&T Automation (Europe) Ltd
CEDIA Home Technology Event 2011
Tuesday 28th June 2011

General Rules

• Please be discrete with mobile phones
• There is no such thing as a silly question!
• Please complete course evaluations at the end
of the class. These help us improve
and evolve the courses
in future years.

Tue, 28th June 2011 CEDIA Expo 2011: Designing the Perfect Rack 2

CEDIA CEU Points

• Once you are CEDIA certified, there is a requirement for
you to get 30 CEDIA CEU points over a 3 year period
following certification. Courses taken before certification
do not count.

• Points are self-managed by logging on the the members
area at www.cedia.co.uk

• All CEDIA courses are eligible for CEU points (1 per hour
of teaching)

• Many manufacturer and distributor courses are eligible
for CEU points - Please check with your CEDIA member
suppliers for details.


Course Contents

• Introduction 15 mins
• Info about T&T
• Aim of this seminar
• Rack building and why do it?

• Anatomy of a Rack 40 mins
• Basic Rack Info
• Rack Types
• Rack Fixings

• Break 5 mins


Course Contents

• Choosing a Rack 15 mins

• Rack Layout 30 mins
• Equipment Layout
• Cable Routing
• Power routing
• Signal routing
• Labeling

• Break 15 mins


Course Contents

• Thermal Management 60 mins
• Abbreviations
• Thermal Energy
• Is it Important?
• General Facts
• Passive Ventilation
• Active ventilation
• Layouts to Avoid
• Shelving & Vents

• Break 5 mins


Course Contents

• Thermal Management 60 mins
• Fans
• Doors
• Filtering
• Ideal System
• Calculations

• Questions 5 mins


INTRODUCTION


Introduction: Info about T&T

• Mainly Residential AV Company
• Multiple Award Winner

• http://www.TandT-eu.com


Introduction: Aim of this Seminar

• Learn:

• Rack components

• Accessories

• Rack planning

• Cable planning

• Thermal Management


Introduction: Rack building and why do it?

Flexibility,
Upgradability & Appearance &
Serviceability Isolation

Thermal & Cable
Management


ANATOMY OF A RACK:
BASIC RACK INFO


Anatomy of a Rack: Basic Rack Info


ANATOMY OF A RACK:
RACK TYPES


Anatomy of a Rack: Rack Types

• Floor Standing Open Rack
• Pros
• Cheap
• Light
• Self assembled or premade
• Easy to fit into tight spaces
• Cons
• Unsecure (No Sides or Doors)
• Not Strong or Robust (bolt together)
• No Protection from dust, sprinklers or Mice!
• No Thermal Draw
• Cheap Appearance

Use if cost or access is an issue, accessories can be added later.



• Floor Standing Closed Rack
• Pros
• Secure
• Robust (welded)
• Protection from dirt, sprinklers and Mice!
• Thermal Draw
• Professional Appearance
• Cons
• More Expensive
• Heavy
• Premade
• Difficult to fit into tight spaces

Use when cost, space or access is NOT an issue



• Wall Mounted Rack

• Pros
• Small
• Quick installation
• Easy access

• Cons
• Weight Limited
• U limited (~12U max)
• Need a sturdy wall (brick etc.)

Use for local Equipment or network patching



• Portable Unprotected Rack
• Pros
• Same Pros as Floor Standing Open Rack
• Movable (castors)
• Often a Floor standing rack with casters added

• Cons
• Same Cons as Floor Standing Open Rack
• Requires Better strain relief

Use if cost, space or access is an issue


ANATOMY OF A RACK:
RACK FIXINGS


Anatomy of a Rack: Rack Fixings

Retaining:

• Mounting Screws or Bolts

• Washers

• Cage Nuts / Clip on Nuts
/ Rack Nuts



Suspending:

• Shelves

• Rack mount

• Rack ears



Covering:

• Vent Panel

• Baffle Panel

• Blank Panel

• Doors & Sides



Rear Suspension:
Combination Rails

• Rear Equipment Mounting
Rails
Accessory Rails

• Accessory Mounting Rails
Equipment Rails
• Combination Rail

Lacing Rails



Cabling:

• Tie / Lacing Bar

• Cable tray

• Mille Ties /
Cable Ties



Security & Convenience:

• Security Covers
• Work Lights
• Casters
• Service Outlets
• PDUs



Grounding:

• Grounding Bars

• Grounding Buses



Rack Interfacing:

• Conduit entrances

• Expandable Nylon sleeving



Other Accesories:

• Fans

• Ducting

• Drawers

• Rain Hoods


Anatomy of a Rack: Quiz

• What is a Mille Tie?

• What is a Vented Baffle?

• What is the standard Width of an AV Rack?

• What’s the tallest rack that will fit in a 7ft or 2.13m high
room (ignoring rack overheads)?


CHOOSING A RACK


Choosing a Rack

• Sort in order of:
• Location & Access


Choosing a Rack

• Sort in order of:

2. Total Size (U)
3. Total Rack Weight
4. Heat Output
5. Client Interaction
6. System


RACK LAYOUT:
EQUIPMENT LAYOUT


Rack Layout: Equipment Layout

• Sort rack considerations in order of:

1. Total Rack Weight



2. Client Interaction



3. Systems



4. Heat output



5. EMI



6. Serviceability


RACK LAYOUT:
CABLE ROUTING


Rack Layout: Cable Routing

43


44


45

Rack Layout: Power Routing

• 12” < distance between signal & power lines

• Run Power & signal cables on opposite sides of
the rack

• Use lacing bars to bring cables to correct side

• 12” > Cables unsupported


Rack Layout: Signal routing


Rack Layout: Labeling


THERMAL MANAGEMENT


Thermal Management: Abrv.

• Air flow, Suction & Pressure

• CFM – Cubic Feet of air per Minute (US but more
common)
• m3/s – Cubic Meters of air per second (UK)
• SP – Static Pressure (Suction of a fan)
• BTU/Hr – British Thermal Units per hour (Heat output)
• MTTF – Mean Time To Failure (also MTBF)

• 1 CFM = 0.0004.72 m3/s
• 12,000 BTU/Hr = 1 Ton of Air Conditioning
• Watt (Power = Volts x Amps) = 3.413 BTU/Hr


THERMAL MANAGEMENT:
THERMAL ENERGY


Thermal Management: Thermal Energy

• What are the 3 types of Energy transfer?

• Convection

• Conduction

• Radiation



• Convection, n

“The transmission of heat caused by movement
of molecules from cool regions to warmer
regions of lower density”
Collins Dictionary

“the flow of heat through a gas or a liquid:
Warm air rises by the process of convection.”
Cambridge Dictionary



• Conduction, n

“the transmission of heat or electricity”
Collins Dictionary

“the transfer of heat between two parts of a
stationary system, caused by a temperature
difference between the parts.”



• Radiation, n

“The energy radiated and emitted by hot
surfaces through electro-magnetic waves.”



• Why Does Hot Air Rise?

Cold
Air
Hot
Air
Convection

Cold
Air

Radiation
Hot Equipment


• Why Does Hot Air Rise?

Convection

Hot Equipment


THERMAL MANAGEMENT:
IS IT IMPORTANT?


Thermal Management: Important?

• Heat is the main reason for equipment failure

• Over 85°F (29°C) a 10°F increase = 40% reduction in
life

• Most analogue equipment can survive higher temps

• Many Amps can work well up to 110°F (43°C)

• Can mar cabinet finishes & veneers, melt glues etc


Thermal Management: General Facts

• Most High Current Equipment is Front intake

• Stratification is zones of heat

• Locations requiring Thermal Management:
• Rack
• Room


THERMAL MANAGEMENT:
PASSIVE VENTILATION


Thermal Management: Passive Ventilation

Passive:
• Pros:
• Cheaper
• Quiet
• Good for smaller racks
• Reliable

• Cons
• Can dissipate 300-500W
• Airflow Modelling is Complex
• Bad for Larger racks



Vented Rear & Top
• Passive
Front

Other Intake Hot Air
Equipment

Leading Amp
Cold Air Manufacturers
recommend
stacking amps
Front Intake
on top of each
Equipment
other!
Rear


• Tips!
• 300 – 500W Heat dissipation
• Placement for thermal management is more
important
• Extensive Venting on Top
• Vent at top and bottom for chimney Effect.
• Place Hot Equipment at bottom to increase air draw
• Place Hot equipment at top if high ambient
temperatures
• Stack Front intake equipment on top of each other
• Do not Put front Venting plates near front intake
equipment
• Avoid Rear intake Equipment


THERMAL MANAGEMENT:
ACTIVE VENTILATION


Thermal Management: Active Ventilation

Active:
• Pros:
• Simpler to Model airflow
• Good for Larger racks
• Unlimited Heat dissipation
• Reduces Condensation &  System Downtime

• Cons
• More Expensive
• Louder
• Excessive for smaller racks



• Tips!
• Unlimited Heat dissipation
• Placement for thermal management is less important
• No venting in Top, sides or rear for 6U except for Fan
Location
• No Rear venting at all
• Can Put front Venting plates near front intake
equipment
• Place Venting plate above top venting passive
equipment
• Top Fan CFM => Σ (Equipment Fan CFMs)
• Place Hot Equipment at top in Hot Ambient Conditions
(Make Sure Rack is Anchor to Prevent Toppling)
• Avoid Rear intake Equipment

Hot Air
• Normal Solid Rear & Top
Front
Situations
Keep Vents at Least 6U
from Rack Fans!
Other Intake
Equipment Remove Vents between
Amplifiers until Rack
CFM Equals or Exceeds
Cold Air Equipment CFM

Use Blank Panels
Front Intake Where Possible to
Equipment increase SP
Rear

Hot Air
• Hot Ambient Solid Rear & Top
Temperatures Front
Rear
Front Intake
Equipment
Use only in Fixed
Racks that will not
Topple due to being
Top-Heavy
Other Intake
Equipment Vented Bottom (Rear,
Front & Sides) Ok

Cold Air


THERMAL MANAGEMENT:
LAYOUTS TO AVOID


Thermal Management: Layouts to Avoid

• Bad Passive!
Front
Hot Air is not pulled up
by hot amps giving a
low Thermal gradient
causing a low CFM!
Cold Air

Putting Vents near
Front Intake
Equipment in Passive
Hot air Loops
Installations Causes
out of vents
“Short-Circuited” Air
and is taken in
Flow!
again!
Rear


• Bad Active!
Front
Fan sucks in cold air
from close proximity
vents

Hot Air Sits in the rack
and is not pulled out
causing equipment to
heat up

Same issue with Rear
Cold Air
intake Systems
Rear

Cold Air Solid Rear & Top
• Active
Front
Rear
Intake! Top to Bottom
Systems
Other Intake Cause “Mixed
Equipment Convection”!

Venting at the
Hot Air
bottom on the
sides is OK.
Rear Intake
Equipment
Rear

THERMAL MANAGEMENT:
SHELVING & VENTS


Thermal Management: Shelving & Vents

• Venting Tips!

• Locate Fans for Maximum suction or SP
• Use Baffled Vents for difficult situations / hot spots
• No Vents Near Front-Intake Equipment in Passive
Systems
• No Vents Near Fans ANYWHERE!
• Vents Possible Near Front-Intake Equipment in Active
Systems
• Vents are 68% open and thus cause friction on airflow



• BIRO Amps in Actively Cooled Systems
(Bottom-In-Rear-Out)
Hot Air
Front

Put Venting Under
Rear-Venting,
Passively Cooled
Cold Air Amps

Bottom Intake
or Non-Fan
Cooled Amps Rear



• BITO Amps in Actively Cooled Systems
(Bottom-In-Top-Out)
Hot Air
Front

Put Venting
Above Top-
Venting, Passively
Cold Air
Cooled Amps

Bottom Intake
or Non-Fan
Cooled Amps Rear



• Shelving Tips!

• Try to use Rack Ears or Rack Mount
• Avoid Stratification
• Use if it intersects natural rise of air
• Use for Bottom In or Out
• equipment
• Use Non Vented Shelves Above
• Top Amp


THERMAL MANAGEMENT:
FANS


Thermal Management: Fans

• CFM & SP

• SP is the suction of the Fan
• Air Flow is the Volume of Air moved per unit of time
• A Fan’s CFM is the Maximum air flow it can Achieve
• Vents and filters Impede air flow and reduce the CFM
• A Fan with a high SP will be more likely to achieve it’s
rated CFM through a rack of vents and Filters
• All Fans have performance curves plotting SP against
CFM
• Blowers have higher SP but are more noisy



• CFM & SP
Air Flow (CFM)

2 Fans in Parallel
2 Fans in Series
Single Fan

Static Pressure



• Multiple Fans

• If using Multiple Fans in
close proximity, Fans must
be regularly maintained
and checked

• Fan Stopping can cause
the whole system to over
heat.

• Additional Reason for
Maintenance Contract



• Fan Control

• Fans will last Longer if temperature controlled

• Less unnecessary air and  dust will be brought in,
causing less downtime

• Proportional Speed Fans will also manage changes in
ambient Temperature better

• Ball-Bearing Fans outlast Sleeve-bearing Fans by 50%



• Tips!
• Avoid putting venting near fans
• Place Fans at top
• Locate Intake fans & vents to prevent stagnation of air
flow
• Bigger Fan = More CFM for same RPM
• Bigger Fan = Quieter for Same CFM
• Pressurise Racks in Dirty Environments
• Multiple fans can cause problems when they fail
unless carefully monitored.
• Ball Bearing Fans are Better than Sleeve Bearing ones
• Install Temperature controlled Fans
• Check MTTF / MTBF values with Manufacturers


THERMAL MANAGEMENT:
DOORS


Thermal Management: Doors

• Use fans with Front intake equipment and doors with
less than 68% openness
• Fully Perforated Front Doors do not hinder Air Flow
• Use Vented Doors with Front Intake Equipment
• Non-Vented Perspex or Metal Doors can be used when
using bottom vented Racks
• Vented Doors can help or hinder air flow depending on
design
• When using a vented door Adding a Fan at the top of
Rack increases Static Pressure not airflow
• Try to Use Lockable Doors to prevent unintentional
changes for racks not needing access


THERMAL MANAGEMENT:
FILTERING


Thermal Management: Filtering

• Tips!

• Hygroscopic dust Failure
• In areas of 65% humidity or more
• London has a humidity range of 70 to 90%
• Dust insulates equipment making it hotter over time
• More important near uncarpeted areas and Bare
concrete floors as dust is not trapped
• Filters require maintenance (Maintenance Contract?)
• Heat exchangers don’t clog and keep contaminants
out


THERMAL MANAGEMENT:
IDEAL SYSTEM


Rack Layout: Ideal System
False
Cold Air Hot Air
Wall
Supply Return

Active Cooling

Quad Rack
Exhaust Fans

Filtered Bottom
Intake

False wall

Racks split into
systems


Rack Layout: Ideal System


THERMAL MANAGEMENT:
CALCULATIONS


Thermal Management: Calculations

1. To Calculate Cooling Requirements in CFM:
1. Determine Power Amplifier Heat outputs
2. Determine Digital equipment Power outputs
3. Sum Waste Heat Values to Give Output Heat Power (W)
4. Convert Heat Power (W) into CFM Values

2. Calculate Cooling requirements in BTU/Hr
(For HVAC)
1. Determine Power Amplifier Heat outputs
2. Determine Digital equipment Power outputs
3. Sum Waste Heat Values to Give Output Heat Power (W)
4. Convert Heat Power (W) into CFM Values



Ways to Calculate Heat Outputs:

1. Determine by measuring

2. Estimate by using Efficiency Factors on Input
Power

3. Estimate by using Output Channels Rated
Power



1. Determine By Measuring:

𝑛

𝑃ℎ𝑒𝑎𝑡 𝑊 = (𝑃𝑖𝑛 𝑘 − 𝑃𝑜𝑢𝑡 𝑘 )
𝑘=1

Where:
Pin = Measured Input power of a device
Pout = Measured Output power of a device
n = Number of devices



2. Estimate by using Efficiency Factors on Input
Power (Usually too High):

Equipment % Efficiency % Power
converted to heat
Digital Equipment 0% 100%

Linear Power 50% 50%
Amplifiers & PSU
Modern Amps 70% 30%



2. Estimate by using Efficiency Factors on Input Power
(Usually too High)

𝑎 𝑏 𝑐

𝑃ℎ𝑒𝑎𝑡 𝑊 = 𝐷𝑥 + 0.5𝐿 𝑦 + 0.3𝑀 𝑧
𝑥=1 𝑦=1 𝑧=1

Where:
D = INPUT Power ratings of Digital Equipment
L = INPUT Power Ratings of Linear Power Amplifiers
M = INPUT Power Ratings of Modern Power Amplifiers
a = number of Digital Devices
b = number of Linear Power Amplifiers
c = number of Modern Power Amplifiers



3. Estimate by using Output Channels Rated Power
(Better Estimation)

𝑚 𝑛

𝑃ℎ𝑒𝑎𝑡(𝑊) = 𝐷𝑥 + 𝐴𝑦
𝑥=1 𝑦=1

Where:
D = INPUT Power ratings of Digital Equipment
A = OUTPUT Power ratings of All Power Amplifier
m = Number of Digital Devices
n = Number of Power Amplifiers



• For Technicians (in CFM)

(PHEAT (kW) * 1760)
CFM 
ΔTc

(PHEAT (kW) * 3160)
CFM 
ΔTF



• For HVAC Systems in BTU/Hr:

BTU/Hr = PHEAT (W) * 3.4

• Often Nomographs can be obtained from
the manufacturer to help calculate BTU/Hr
& CFM



Example System:

Equipment Quantity Rating
CD Player 1 100W (240V @ 0.416A Input)
Equaliser 1 100W (240V @ 0.416A Input)
Power Amp 4 250W Dual-Channel



Example System:

m n
PHEAT   (D )   (A )
x 1
x
y 1
y

= 100W + 100W + (4 * 2 * 250W)
= 100W + 100W + (2000W)
= 2200W
PHEAT = 2.2kW (Heat)



Example System:

(𝑃ℎ𝑒𝑎𝑡 𝑘𝑊 ∗ 1760)
𝐶𝐹𝑀 =
∆𝑇𝑐

(2.2𝑘𝑊 ∗ 1760)
𝐶𝐹𝑀 =
10℃

(3872)
𝐶𝐹𝑀 =
10℃
𝑪𝑭𝑴 = 𝟑𝟖𝟕. 𝟐℃



• Example System

BTU/Hr = 2200W * 3.4 = 7480 BTU/Hr

CFM = 387.2 CFM

• Due to the following reasons:
• System Impedance will reduce the CFM Figure
• Estimated Modelling is not perfect
• Allowance of Headroom

This figure should be increased by 25% to 484 CFM (500
CFM)


• If Air Conditioning is used we can stand to have
a larger Temperature rise e.g.:

• Air Cooled to 10°C will allow 20°C rise to 30°C
(~85°F)
• CFM is there fore not as much:

(2.2kW * 1760)
CFM 
20C

CFM = 193.6 CFM (250 CFM in
practice)

RACK GROUNDING


Rack Grounding: Abbreviations

• General Terminology
• CMRR - Common Mode Rejection Ratio
• SCIN - Shield Current Induced Noise


Rack Grounding

• AV equipment more affected
• Unbalanced always susceptible
• Balanced susceptible if not correctly wired
• SCIN mainly in long runs
• Connecting both ends creates a ground loop
• Disconnecting one end allows shield to act as an
antenna.
• Recommended solution is to use a 0.1uF Cap


Rack Grounding

• Crosstalk = signal coupling from one core / cable to
another in close proximity
• Telecoms cable can also radiate EMI from internal
sources

• 2 x facts
• There will always be a (small) potential difference (voltage) between
2 grounded devices
• There is always a (small) current flow in the signal cables of 2
grounded devices

• Audio Symptoms = audible Hum or buzz
• Video Symptoms = visible hum bars


Rack Grounding

• Unbalanced Cables
• Most cable interfaces in general consumer AV industry are
unbalanced
• Power line noise current and audio signal share the external shield
of an unbalanced cable causing the noise to be added to the
signal. This is called common-impedance coupling
• Avoid unbalanced connections where possible
• Keep cables short < few feet
• Heavy braided cables are better than foil & drain wire
• Use a high quality signal isolation transformer at receiver end
• Do Not disconnect sheild at either end of unbalanced cable


Rack Grounding

• Balanced Cables
• Balanced usually use XL or screw-down type connectors
• Noise / Interference is transmitted over all cores
• Cable shields do not protect against low (power and audio)
frequency AC magnetic fields

• NEVER LIFT, OR OTHERWISE BYPASS THE POWER CORD
GROUND… IT COULD BE FATAL!

• Use cables with properly grounded cable shields (only effective
against electric fields, not magnetic fields)
• 2. Use low-impedance balanced signal connections
• 3. Follow good signal path design and installation practices


Rack Grounding

• Causes of excessive Ground loops
• Bad cable connection
• Bad cable location (proximity to transformers or EMI sources)
• Bad design of the main power and grounding system
• Large printed circuit trace loop areas are susceptible to voltage
induction usually found on poorly designed equipment. These
circuit trace loops can cause hum even when there is no ground
loop present, and even when there is no power to the equipment
• Best practices of good signal path design include good cable
management inside the rack. With the exception of
wellconstructed coaxial cable (which is inherently immune to low-
frequency AC magnetic fields), it is recommended that signal
cables are placed a minimum of 2” away from AC power
conductors when run parallel. It is, however, acceptable to install
signal cables in close proximity to power cables if the conductors of
both cables are twisted tightly.
• Some equipment is designed to pass leakage currents onto the
ground circuit. This current may manifest itself as a hum or buzz in
poorly designed AV systems.

Rack Grounding

• The most common way to detect receptacle wiring errors is with a
threeprong receptacle tester. However, “three prong” receptacle
testers (like that shown below) cannot detect a neutral-ground reversal
or a bootleg ground. A reversal or bootleg groundcan be a significant
cause of system noise and can only be detected by using an amp
meter as detailed in the NeutralGround Reversals and Bootleg Grounds
section of this paper.


Rack Grounding

• Power Cabling
• Flexible Metallic Tubing/Conduit – Commonly called “Greenfield” after the name of its inventor, this type of raceway has limits as to the
use of the conduit as a grounding conductor. A supplemental grounding conductor is generally required on lengths over 6 ft. For AV
installations it is recommended to use an insulated ground wire when metallic conduit is required or specified.
• Armor Clad – Designated (AC) by the NEC, and sometimes called “BX”, its original manufacturer‟s trade name. While it is the least
expensive, is the least desirable for AV systems due to the fact that there is no supplemental grounding conductor (wire). The metal
jacket, along with its aluminum bonding strip, is the safety grounding conductor and is detrimental to AV performance due to its higher
comparative impedance than a solid piece of copper wire. Without a supplemental grounding conductor, the ground impedance and
integrity is dependent on the length of the sheath and all the connectors and fittings (in series). BX cannot be used with isolated ground
receptacles.
• Non-Metallic Sheath - designated (NM) by the NEC and commonly called Romex, is not permitted in places of assembly or in buildings
of 3 or more floors. Romex cannot be used with isolated ground receptacles.
• Metallic Conduit must be installed as a complete system before the wiring is installed. The conduit is considered a “grounding
conductor.” A supplemental grounding conductor may be installed. For AV installations it is recommended to use an insulated ground
wire when metallic conduit is required or specified.
• Metal Clad (MC) is manufactured in both steel and aluminum with twisted conductors that help reduce AC magnetic fields. Although the
steel jacket helps reduce AC magnetic fields, the twisting of conductors has the greatest effect on reducing these fields. Another benefit
is the constant symmetry of the phase conductors with respect to the grounding conductor which greatly reduces voltage induction on
the grounding wire.
• Two conductor plus 1 ground MC (Metal Clad) is a good choice for Non-Isolated Ground A/V systems. MC cable contains a safety
grounding conductor (wire). The three conductors in the MC cable (Line, Neutral and Ground) are uniformly twisted, reducing both
induced voltages on the ground wire and radiated AC magnetic fields. The NEC article 250.118 (10)a prohibits the use of this cable for
isolated ground circuits because the metal jacket is not considered a grounding conductor, and it is not rated for fault current.
• Two Conductor plus 2 ground MC (Metal Clad) may be used in an Isolated Ground installation, because the cable contains two
grounding conductors (one for safety ground and one for isolated ground). The conductors are twisted, but the average proximity of the
hot conductor and the neutral conductor with respect to the isolated grounding conductor is not equal. Under load, this will induce a
voltage along the length of the isolated ground wire, partially defeating the intent of isolation (see Ground Voltage Induction section of this
paper)
• Armor Clad for Healthcare Facilities (AC-HCF) Aluminum Armor Clad for Healthcare Facilities (AC-HCF) is the best choice for Isolated
Ground A/V systems. Like MC, it contains an additional grounding conductor, although with this type of cable it is permissible to use the
metal jacket as the safety grounding conductor, as required with isolated ground installations. The biggest benefit is that the average
proximity of the hot conductor and the neutral conductor with respect to the isolated equipment grounding conductor is nearly equal,
virtually eliminating ground voltage induction (GVI), even on long runs.
• Steel Armor Clad for Healthcare Facilities (AC-HCF)Similar to aluminum armor clad AC-HCF, but does not address ground voltage
induction as effectively as aluminum (see Ground Voltage Induction section of this paper). Two other problems are that steel clad is not
readily available and is cumbersome to transport and install.


Rack Grounding

• The only ways to reduce the effect of AC magnetic fields are through physical separation (distance), tightly twisting the conductors, or
encasing them in ferrous tubing such as steel

• Best practices dictate that equipment racks must be bonded together. Per the NEC (Article 640) or Authority Having Jurisdiction, it is
best to bond ganged racks together with paint-piercing hardware and purchase racks with pre-installed ground studs for convenience
and to ensure good conductivity.

• Most AV installations benefit from a dedicated shielded isolation transformer with a single ground reference point. The transformer will
be a buffer between the utility company and facility electrical system and the protected electronics systems such as AV equipment
control electronics, dimmers and data devices.

• All transformers have capacitance between the primary and secondary windings, which allows higher frequencies of common-mode
noise to pass – as shown in the diagram above left. Utilizing an electrostatic (Faraday) shield between the windings reduces this
capacitance and provides a path for the noise to flow back to its source - as shown in the diagram above right.


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CEDIA Home Technology Event 2011: Designing the Perfect Rack