D jav grounding
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The document discusses grounding of airport lighting systems. It defines grounding and its objective to achieve the lowest possible ground resistance economically. Standards from the National Electrical Code (NEC) and FAA recommend a ground resistance of 25 ohms or less and 10 ohms or lower, respectively. Soil resistivity is measured to calculate the required ground rod configuration to meet the resistance targets. Proper grounding design, testing, and improvement of the design process are emphasized.
D jav grounding
- 1. Grounding of Airfie ld Lig hting Joseph Vigilante, PE Penn State/ FAA Hershey Conference 2009
- 2. Grounding of Airfie ld Lig hting “In the Fairytale of electrical design, Grounding is the Ugly Duckling.” ? Definition ? Objective ? Standards ? Recommended Values ? Soil Resistivity ? Calculation ? Design ? Summary
- 3. Grounding of Airfie ld Lig hting NEC 2 5 0 .2 – Effe ctiv e Ground-Fa ult Curre nt Pa th “An intentionally constructed, low impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the OCPD or GFD on high-impedance grounded systems.”
- 4. Grounding of Airfie ld Lig hting The Obje ctiv e : In ground system design, the objective is to achieve the lowest ground resistance value possible that makes sense economically and physically.
- 5. Grounding of Airfie ld Lig hting Sta nda rds : ? National Electrical Code (NEC) ? FAA AC 150/ 5340-30D ? FAA-STD-19e – Lightning and Surge protection, Grounding, Bonding and Shielding Requirements for Facilities And Electronic Equipment
- 6. Grounding of Airfie ld Lig hting Na tiona l Ele ctrica l Code ( NEC) 2 5 0 .5 6 A single electrode consisting of a rod…that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode…
- 7. Grounding of Airfie ld Lig hting NEC 2 5 0 .5 3 & 5 8 … Two or more grounding electrodes that are . bonded together shall be considered a single grounding electrode system.
- 8. Grounding of Airfie ld Lig hting FAA AC 1 5 0 /5 3 4 0 -3 0 D 1 2 .6 . SAFETY ( EQUIPMENT) GROUND …A safety ground must be installed at each light fixture… The safety ground must be a . #6 AWG bare jumper connected to the ground lug at the fixture base or stake to a 5/ 8 inch (16 mm) by 8 foot (2.4 m) minimum ground rod installed beside the fixture. The resistance to ground of the stake must be 25 ohms or less per measurement with a ground tester.
- 9. Grounding of Airfie ld Lig hting FAA -STD- 1 9 e Se ction 4 .2 .4 Ea rth Ele ctrode Sy s te m Re quire me nts Sub-s e ction 4 .2 .4 .3 De s ig n ….The design goal for the resistance to earth of the EES shall be as low as practicable and not over 10 ohms.
- 10. Grounding of Airfie ld Lig hting Re comme nde d Va lue s : Using a 20% buffer, Design Range is 10-20 ohms
- 11. Grounding of Airfie ld Lig hting Soil Resistivity Measurement ρ = ( 2 ) ( п) ( A) ( R) ρ = Average Soil Resistance to Depth A in ohm-cm A = Distance between Electrodes in cm R= Measured Resistance Value in ohms Using a 3 m (10’) Ground Rod, Assume R measured value of 100 Ω ρ = 2 x 3 .1 4 1 6 x 3 m x 1 0 0 Ω = 1 8 8 5 Ω·m
- 12. Grounding of Airfie ld Lig hting Soil Resistivity Tabulated Boring Log ? 0 – 2ft – Poorly Graded Gravel ? 2 – 4 ft – Sandy Lean Clay w/ Gravel ? 4 – 13 ft – Silty Sand
- 13. Grounding of Airfie ld Lig hting Soil Resistivity Tabulated Type of Soil Soil ? Data table Resistivity - Ω·cm ? Average values Poorly graded 100k – 250k ? Non-specific to site gravel, gravel/sand mix Well graded gravel 60k – 100k Silty Sands 10k – 50k Silty Soils 8k – 30k Clayey Sands 5k – 20k Clayey Fine Sands 3k – 8k Rock 10M
- 14. Grounding of Airfie ld Lig hting Soil Resistivity Tabulated Type of Soil Soil ? 10 ft. ground rod Resistivity - Ω·cm ? 0 – 2ft – Poorly Poorly graded 100k – 250k Graded Gravel gravel, gravel/sand mix ? 2 – 4 ft – Sandy Lean Well graded gravel 60k – 100k Clay w/ Gravel Silty Sands 10k – 50k ? 4 – 13 ft – Silty Sand Silty Soils 8k – 30k Clayey Sands 5k – 20k Clayey Fine Sands 3k – 8k Rock 10M
- 15. Grounding of Airfie ld Lig hting Resistance To Ground ? IEEE Green Book Chapter 4 ? 10 ft (3m) Ground Rod, 5/ 8” Diameter ? Rg = ρ / (2 x п x L x ln (4L/ a -1)) ? Rg = ρ (Ω·cm) / 335 cm
- 16. Grounding of Airfie ld Lig hting Range of Soil Resistivity ? Rg = 10 Ω – 20 Ω ? ρ = Rg (Low) x 335 cm - Rg (High) x 335 cm ? ρ (Ω·cm) = 3350 Ω·cm - 6700 Ω·cm
- 17. Grounding of Airfie ld Lig hting Ground Resistance Adjusted ? ρ = 10,000 Ω·cm ? Rg = 10kΩ·cm / 335 = 29.8 Ω ? IEEE Chapter 4, Multiple Rods Factor ? Using 2 Rods: Rg (adjusted) = (Rg/ 2) x 1.16 ? Rg (adjusted) = 17.3 Ω
- 18. Grounding of Airfie ld Lig hting Bonding Jumper ? #6 AWG , Bare Copper ? NEC Table 8 Conductor Properties ? 0.491 Ω/kFT
- 19. Grounding of Airfie ld Lig hting Grounding System ? 2 Ground Rods At Each Location ? 500 FT Spacing ? #6 AWG , Bare Copper
- 20. Grounding of Airfie ld Lig hting Summary ? Obtain Boring Reports ? Field Measure Soil Resistivity ? Calculate Ground Resistance ? Specify Ground Resistance Testing – During Installation and After ? Obtain and Review Results ? Improve Your Design Process
- 21. Grounding of Airfie ld Lig hting Questions?