Fields and Waves I

GroundingZero Reference and Safety

K. A. ConnorElectrical, Computer, and Systems Engineering Department

Rensselaer Polytechnic Institute, Troy, NY

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Grounding

ExamplesLightningCurrent FlowResistance

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Grounding of Electrical Systems

Electrical Systems Require a Solid Ground

The Ground Connection Has a Finite Resistance

As Current Flows Away From the Ground Rod, the Voltage Drops to Zero

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Examples

Grounding Can Occur at Several Locations

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Grounds are Most Often Provided by Driving a Conducting Rod Into the Ground

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Lightning

Continent Country / State strikes / km² / yr

Africa Dem Rep of Congo 158South

America Columbia 110

Asia Northern Pakistan 87

North America USA / Florida 59

Europe Northern Italy 28

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Lightning

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Current Flow From Ground Rod

The current flows into the soilThe contact with the soil has a finite resistanceDriving a large current (from lightning) will produce a very large voltage

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Calculating Resistance

Recall the resistance of a cylinder of length L and area A

What is the resistance of a hemisphere?

RLA

LA

= =ρ

σ

NEC guidelines require the ground resistance to be less than 25 Ohms.

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Stoneridge Engineeringhttp://205.243.100.155/frames/home.html

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References

Wikipedia• Ground• Resistance

Ground Rods & Grounding• From Hubbell• From USDA• From IEEE• From Fluke

IEEE Standard 142-2007