grounding[a]

7/28/2019 Grounding[a]

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Grounding of Electrical

Systems

NEW CODE: Grounding andBonding

Presented ByScott Peele PE


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Grounding of Electrical

Systems Outline

z Defining the Terms

z Why should I Ground?

z Types of Grounding Systems

z Separately Derive Systemz Grounding Electrode

z Bonding

z Ground Fault Protection

z Ground Reference or Signal Reference

z Grounding for Lightning Protection


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Definitions

z Review definition as we encounter them.

z Grounded vs Groundingz Isolated Ground

z

Floating Groundz Ground Loop

z Net Current


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Why am I grounding or Not?

z Safety

z Grounding for Fault Current Pathsz Grounding for Touch Potential (static)

z

Grounding for Lightning Protection SurgeArresters, TVSS (SPD)

z Grounding for Signal Reference (RF, Data,

static ,etc.)z Not Grounding Continuous operation


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Three reasons for grounding

FaultProtection

Lightning

Protection

Signal

Reference


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Grounded vs Grounding

z Grounded vs. grounding in an electricalsystem. Grounded system refers to a

system where a conductor is groundedand is intended to or may carry current inthe normal operation. The neutral on a

wye system is a prime example of agrounded conductor.

zThe grounding conductor system is not

intended to carry operational current in itsdesign. This path is intended to carryunwanted and fault currents for protection.


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Types of AC Grounded Systems

z Ungrounded system

z Solidly Grounded Systemz Resistance Grounded

z Reactance Grounded

z Ground Fault Neutralizer


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Which System to Use??

z Safety - Who is Operating the System

z Ground Fault Detectionz Signal Reference

zTouch Potential (also static)

z Available Fault Currents?

z Operation Stability

z System Response


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Ungrounded System

zType of system typically used on is aDelta service.

z Some time used on a floating Wye

z Detection System in Place

Ground Detection by Lighting

Zigzag Grounding Transformer

Ground Relay Ground Fault ???


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Detection Devices


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Solidly Grounded System

z Usually use in Wye systems

z Return Fault current to trip overcurrentprotection device quickly

z Usually better reference and safer system

z Much better for lightning protection

z Can be used in Corner Grounded Delta

Problems with phase grounded re-grounded Not good on lightning protection equipment


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Resistive grounded

z Low Resistance

Limit Fault Current

Minimizes the damage at the fault

Used usually with multiple sources i.e.transformers, and or generators

z High Resistance

Enables system operation with one phasegrounded

Enables current to flow for detection networks

Current is low enough so that no damage occurs


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Reactance Grounding

z Reactor connected between systemneutral and ground

Reduces the ground fault current betweenphase and ground

Usually higher fault current than lowresistance grounding

Better coordination with fault currents on

multi-grounded system. Mostly used onsystem above 5kV.


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Ground-Fault Neutalizer

z Reactor with relatively high value ofreactance.

z Usually on system above 15kV phase toground air exposed. (overhead

Transmission and Distribution)z May provide insulator flashover with self-

extinguishing characteristics.


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Separately Derived System

zThe system grounding conductor for aseparately derived system shall begrounded at only one point.

z Main system Disconnecting means for a

main utility feed, or a step down or step uptransformer, or a generator could all beseparately derived systems.

z When grounded it will be grounded at thenearest grounding electrode.


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Grounding Electrode System and

Grounding Electrode Conductor Part IIIz NEC 250.50 (Grounding Electrode System) 250.52 Electrodes

Water Pipe if 10 ft. or more of metal water pipe is in contactwith the earth.

Metal Frame of the Building or Structure where the followingmethods are used to make an earth connection: (1,2,3,4)

Concrete-Encased Electrode in at least 2 of concretelocated within and near the bottom of a concrete foundationor footing that is in indirect contact with the earth.

Ground Ring encircling the building or structure in directcontact with the earth

Rod or Pipe electrode not less than 8 ft in length Plate Electrode not less than 2 square ft.

Other Local underground systems such as piping,underground tanks and underground metal well casing NOT Permitted

Metal underground gas piping

Aluminum electrode


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Grounding Electrode System

z Installation NEC 250.53

This requirement clarifies that thesupplemental electrode system must beinstalled as if it were the sole groundingelectrode

z Bonding NEC 250.53 C

This requirement is for bonding of

multiple electrodes.


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Bonding

z Bonding for

Main Bonding J umper System Bonding J umper

Electrode Bonding

Part V Bonding

Where necessary to ensure electrical continuityand the capacity to conduct safely and faultcurrent likely imposed.


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Ground ?

HotNeutralGround


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Review Ohms Law

Voltage = Current X Resistance

(ohms)(Potential) (amps)

DevelopVOLTAGE

DevelopVOLTAGE

BONDING

GroundRod

GroundRod

Current Source Lightning

Average current 30,000 amps


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Grounding and Bonding

Transient voltages andTransient voltages andcurrentscurrents at data port orcable connections

Voltage Difference


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Isolated Ground

z NEC 250.146 (D) Isolated groundreceptacle (orange triangle) NEC 406.2(D)

z NEC 250.96 (B) Isolated GroundingCircuits

z NEC 647 Section Sensitive ElectronicEquipment.

z NEC 647.6 Grounding.

Technical Equipment Ground


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Isolated Ground

Isolated grounded receptacle has an isolated terminal from the yoke to the groundLug. These receptacle are usually marked with an orange triangle or all orange.

Sub Panel

Ground Bus

Neutral Bus


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Floating Ground

zThe neutral on a wye system is notintentionally grounded

z Signal conductor shielding is notintentionally grounded

z Problem is high transient voltage orovervoltages may exist causing damage.

z Not a good way for lightning protection

G d L


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Ground Loop

z Grounds from two different derived systemare connected

z Open ground loops. Grounds are notbonded properly and cause damage.

z Ground loops cause circulating currentbetween systems and cause transformercoupling (CTs)

z Signal reference can be compromisedcausing data errors.

G di f Si l R f


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Grounding for Signal Reference

z Dont Burst the Bubble.

z

Ground on one endz Ground on both ends

z Ground on neither end

z Fiber Optic Best Answer

z Optical Coupler

D t B t th B bbl


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Dont Burst the Bubble

G d F lt I t t F ti


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Ground Fault Interrupter Function

Net Current


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Net Current

z Currents that are not apart of the normaloperation of a derive electrical system.

All positive, negative, and zero sequencecurrents added and the resultant currentare net currents.

Books On Grounding


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Books On Grounding

z NEC

z IEEE Green Book 142-1991Recommended Practice for

Grounding of Industrial and Commercial Power

Systems Emerald Book 1100-1999 Recommended

Practice for Powering and Grounding SensitiveElectronic Equipment

z Industrial and Commercial Power systemHandbook

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