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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