Data Quality and Grounding Considerations in a Mixed-Use Facility
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Transcript of Data Quality and Grounding Considerations in a Mixed-Use Facility
Data Quality andGrounding Considerations
ina Mixed-Use Facility
Robert A Durham, PERobert A Durham, PE
DD22 Tech Solutions, Inc. Tech Solutions, Inc.
Tulsa, OKTulsa, OK
Marcus O Durham, PhD, PEMarcus O Durham, PhD, PE
THEWAY Corp / U TulsaTHEWAY Corp / U Tulsa
Tulsa, OKTulsa, OK
Facilities: depend heavily on networksProblems: signal quality & noiseIssues: electrical safety & codeSystems: eleven different groundsAttention: bonding, isolate earth & power
Facilities: depend heavily on networksProblems: signal quality & noiseIssues: electrical safety & codeSystems: eleven different groundsAttention: bonding, isolate earth & power
AbstractAbstract
All for onePower co, Telco, Computer groupInstall for parochial interestInterferes w/ sensitive network
Traditional power & personnel safetyComputer & Communication
Lower levels & higher freqGrounding – Do Not connect all together
Gordian KnotGordian Knot
Grounding metal path, call ground metal & earth
Grounded current carrying neutral, common
Shielding metal around signal intercept noise
Bonding possible energized between metal
Transient equal potential grid lightning, etc
Types of Ground TermsTypes of Ground Terms
ApplicationApplication
Requirements of systems quite differentSystems power, comm, data, EMI &
RFIGround convenient common ptBonding eliminate potentialArrangement limit circulating currents
Most susceptible systems are often cause• Switched mode power supply (SMPS)• On sensitive electronics
Non-linear load causes harmonicsNeutral noise & poor power qualityFix
• 12 pulse• Isolation transformer
Susceptible & CauseSusceptible & Cause
“ The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.”
Article 90
National Electric CodeNational Electric Code
National Electric CodeArticle 250
National Electric CodeArticle 250
>25 pages groundingOther pages neutral, transients, specifics
R.I.P.
National Electric CodeConcern
National Electric CodeConcern
Allows 25 Ω power groundOn 120 volt circuit
I = 120 V / 25 Ω = 4.8 AWill not trip 20AShock at 6 mATarget 1 Ω
JulyJuly AugustAugust
ReferenceReference
Single point Accessible Insulated from other metal Bond back to here Reference point for all systems
Eleven Grounding Systems
1. Building structural steel1. Building structural steel2. Electrical enclosure grounding conductor2. Electrical enclosure grounding conductor
6. Telephone reference gnd6. Telephone reference gnd
9. Shielding9. Shielding
3. Transformer wye common3. Transformer wye common4. Neutral at main4. Neutral at main5. Transient protection gnd5. Transient protection gnd
11. Network equi-potential reference gnd11. Network equi-potential reference gnd
8. Back-up battery common8. Back-up battery common7. Data (dc) power common7. Data (dc) power common
10. Isolated (ac) power gnd10. Isolated (ac) power gnd
Ground DesignGround Design11 Unique pointsShows complexity of EE – bond & isolateAll insulated to prevent shorting
except enclosureConductor size
fault current
inductance w/ transient freqConduit bonds & isolationBond non-electrical metal w/in 6’
EE
NeutralNeutral
White, current carryingGround at main disconnect ONLYIsolate at sub-panels
• if not, circulating current in groundHarmonic analysis
• affects size of neutral• may need filter or isolation xformer
Transformer main distribution
Hot H
Neutral N
Ground G
wye bond
single point
CommunicationsCommunications
Includes instrumentation & networksMore sensitive to noise, transients, shiftsBoth analog & digitalIsolated from power groundSpecial considerations
• cable tray & racks• isolated earth• isolated power
Ground NoiseGround Noise
Much of noise introduced from groundSystem imbalance contributesHarmonics travel through grounding
conductorsIsolated ground reduces noise
Uncontrolled Ground PathsUncontrolled Ground Paths
3 sources of electrical connection• ac power• cable tray• building metal – not grounding
conductorSeparate groundsAll wire insulated
Equipment Room GroundingEquipment Room Grounding
Star design radial
For small close
One-point
Bus bar, visible, insulatedRat race ring
For larger area
Equi-potential
Ground 2+ locations
More RobustMore Robust
Isolated insulated conductors around roomConnect to isolated triad @ 2 ptsOne rack – single ground conductor
RACK 1 RACK 2
CHASSIS CHASSIS
POWERSUPPLY24 VDC
+ 24
- COM
TERMINATIONTELEPHONETERMINATION
RADIO
RADIO 1
RADIO 2
TELE 1
TELE 2
CONNECTION
GROUND ROD
SURGE PROTECTOR
Racks and Raceways Racks and Raceways
1. Insulated conductor
2. Conductor along each tray
3. Connect each rack – 2 locationsRemove paint
Fix connector & bolt
4. Each chassis bond to rack
Jumper or strip
5. Crimp connectors & reinsulate
6. NEVER allow wire to touch metal
Isolated Earth Ground Isolated Earth Ground
Triad earth w/ 3 rodsSpace 2.2 * length6’ separation from metalConnect w/ uninsulated copperExothermic weld connections
ACME
CONCRETE
Ring Bus
Isolated Earth GroundIsolated Earth GroundRun #1 corner to equipment roomRun another different routeRun #3 corner to reference ground
remove if interference per NEC Green insulated wireContinuous - no underground spliceBends – minimize Z
> 8” radiusMinimize # to reduce L
Buffer dissimilar metals to reduce R
Isolated PowerIsolated PowerNot always req’dAll electrical power & ground isolate from
external metal1:1 transformer
Connect w/ pvc – provides isolationNo building ground here
New distribution panel on insulated sheetTransient protectionUse isolated groundReceptacles w/in racks
PVC PVC
Power H
Power N
Ground
Power H
Power N
Ground
Main
IsolatedDistribution
Cathodic ProtectionCathodic Protection
CP applied to some metal in earthProvides low Z Path to earthCannot bond to other metal
– would short CP– If necessary to bond, use resistor
• prevents use as fault path• better than open circuit
Has inherent personnel protection
ConclusionsConclusionsEffective data quality & grounding considers
neutralpowerbondingshieldingtransient
Ground path < 1Ω
ConclusionsConclusionsSpecial consideration
grounding enclosure – rackequi-potential earth groundconsider isolated electrical
Analog & digital separate
ConclusionsConclusionsReference ground for interconnection of
structure enclosurewye neutraltransient telephonedata batteryshielding isolatedequi-potential
QUESTIONS?QUESTIONS?