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?