Data Quality and Grounding Considerations in a Mixed-Use Facility

1. Data Quality andGrounding Considerations ina Mixed-Use Facility Marcus O Durham, PhD, PE THEWAY Corp / U Tulsa Tulsa, OK Robert A Durham, PE D2 Tech Solutions, Inc. Tulsa, OK

2. Abstract • Facilities: depend heavily on networks • Problems: signal quality & noise • Issues: electrical safety & code • Systems: eleven different grounds • Attention: bonding, isolate earth & power

3. Gordian Knot • All for one • Power co, Telco, Computer group • Install for parochial interest • Interferes w/ sensitive network • Traditional power & personnel safety • Computer & Communication • Lower levels & higher freq • Grounding – Do Not connect all together

4. Types of Ground Terms

5. Application • Requirements of systems quite different • Systems power, comm, data, EMI & RFI • Ground convenient common pt • Bonding eliminate potential • Arrangement limit circulating currents

6. Susceptible & Cause • Most susceptible systems are often cause • Switched mode power supply (SMPS) • On sensitive electronics • Non-linear load causes harmonics • Neutral noise & poor power quality • Fix • 12 pulse • Isolation transformer

7. National Electric Code “ The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.” Article 90

8. National Electric CodeArticle 250 • >25 pages grounding • Other pages neutral, transients, specifics

9. R.I.P. National Electric CodeConcern • Allows 25 Ω power ground • On 120 volt circuit I = 120 V / 25 Ω = 4.8 A • Will not trip 20A • Shock at 6 mA • Target 1 Ω

10. July August

11. Reference • Single point • Accessible • Insulated from other metal • Bond back to here • Reference point for all systems

12. Eleven Grounding Systems 1. Building structural steel 2. Electrical enclosure grounding conductor 3. Transformer wye common 4. Neutral at main 5. Transient protection gnd 6. Telephone reference gnd 7. Data (dc) power common 8. Back-up battery common 9. Shielding 10. Isolated (ac) power gnd 11. Network equi-potential reference gnd

13. EE Ground Design • 11 Unique points • Shows complexity of EE – bond & isolate • All insulated to prevent shorting except enclosure • Conductor size fault current inductance w/ transient freq • Conduit bonds & isolation • Bond non-electrical metal w/in 6’

14. Neutral • White, current carrying • Ground at main disconnect ONLY • Isolate at sub-panels • if not, circulating current in ground • Harmonic analysis • affects size of neutral • may need filter or isolation xformer

15. Transformer main distribution Hot H Neutral N Ground G wye bond single point

16. Communications • Includes instrumentation & networks • More sensitive to noise, transients, shifts • Both analog & digital • Isolated from power ground • Special considerations • cable tray & racks • isolated earth • isolated power

17. Ground Noise • Much of noise introduced from ground • System imbalance contributes • Harmonics travel through grounding conductors • Isolated ground reduces noise

18. Uncontrolled Ground Paths • 3 sources of electrical connection • ac power • cable tray • building metal – not grounding conductor • Separate grounds • All wire insulated

19. Equipment Room Grounding • Star design radial For small close One-point Bus bar, visible, insulated • Rat race ring For larger area Equi-potential Ground 2+ locations

20. More Robust • Isolated insulated conductors around room • Connect to isolated triad @ 2 pts • One rack – single ground conductor

22. Racks and Raceways • Insulated conductor • Conductor along each tray • Connect each rack – 2 locations Remove paint Fix connector & bolt • Each chassis bond to rack Jumper or strip • Crimp connectors & reinsulate • NEVER allow wire to touch metal

23. ACME CONCRETE Ring Bus Isolated Earth Ground • Triad earth w/ 3 rods • Space 2.2 * length • 6’ separation from metal • Connect w/ uninsulated copper • Exothermic weld connections

24. Isolated Earth Ground • Run #1 corner to equipment room • Run another different route • Run #3 corner to reference ground remove if interference per NEC • Green insulated wire • Continuous - no underground splice • Bends – minimize Z > 8” radius Minimize # to reduce L • Buffer dissimilar metals to reduce R

25. Isolated Power • Not always req’d • All electrical power & ground isolate from external metal • 1:1 transformer Connect w/ pvc – provides isolation No building ground here • New distribution panel on insulated sheet • Transient protection • Use isolated ground • Receptacles w/in racks

26. Power H Power H Power N Power N Ground Ground PVC PVC Isolated Distribution Main

27. Cathodic Protection • CP applied to some metal in earth • Provides low Z Path to earth • Cannot 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

28. Conclusions • Effective data quality & grounding considers neutral power bonding shielding transient • Ground path < 1Ω

29. Conclusions • Special consideration grounding enclosure – rack equi-potential earth ground consider isolated electrical • Analog & digital separate

30. Conclusions • Reference ground for interconnection of structure enclosure wye neutral transient telephone data battery shielding isolated equi-potential

31. QUESTIONS?