Is Grounding the Culprit
Marcus O. Durham, PhD, PE
Robert A. Durham, PhD, PE
ThewayCorp.com





What is the purpose of grounding?
Can grounding issues cause ignition or shock?
Where is a ground or return path used?
What is the difference between ground, bond, & neutral?
1
2
4
3
8
9
10
12
11
M.O. Durham
Theway Corp.
5
6
7

 Complex Topic
 Critical for electrical safety
 Biologic
 Property




NEC - > 28 pages
NESC – Specific Requirements
IEEE – Multiple Standards
NFPA – Myriad Publications

 Grounding is major element of every electrical system, but rarely understood

“Hot” cause shock or ignition only with return path – complete circuit
 Either neutral (controlled) or ground
(uncontrolled) provides return
 Electrical activity on neutral or ground – fault involving ground system
 Ground is code and legal issue

 Three components
 Grounding Electrode
 Contact point with earth
○
○
○
NEC <25 Ω or additional electrode required
NESC - < 25 Ω.
IEEE 142 - 25 Ω not satisfactory – 1-5Ω
 Grounding Electrode Conductor
 Connects grounding electrode to system
 Must handle fault currents – NEC size
Z

V

I
120 V
20 A

 Bonding



Connects metal surfaces to grounding system
Required between grounding electrodes
NEC FPN –bond all metal even if not specified
Vd
I
 Without bond –
 Potential difference exists between metals
 Potential difference causes current flow



Current carrying conductor
Controlled return path for 1 Φ & DC


Single point connection to ground
If multiple points –

 current flows through grounding system
If poor connection –
Transformer  circuit current can flow Entrance
Power H through ground
Neutral
Power H
Ground
Utility
Ground
Service
Ground
Load
Power H
Neutral
Ground
Water &
Other
Metal

 Unintentional current flow through earth
 Three causes


Neutral grounded at multiple points
Fault of “hot” wire to ground
 Difference in potential of ground connections
 Multi grounded neutral allows ~60% return current in earth
 Allows V between metals and between metal and earth



Portion of I n flows through earth
Disturbances cause I flow in alternate routes
 Risk of shock or equipment damage
I n

 Short duration disturbances
 Should be shunted to ground
 Causes
 Lightning
 Utility Operations
 Every On/Off of electrical circuit



Lightning is natural phenomena
Uncontrolled – damage
 Can be controlled


Industry standards and practices
Controlled – no or limited damage

 Three issues
 Energized Ground
 Floating Neutral
 Energized Neutral
 Energized Ground
 I from another circuit
 Caused by poor cnxns and poor ground Z
 Melted insulation on ground wire or jacket

 Floating Neutral
 Poor N connection
 Allows return current on alternate path
 Uncontrolled V levels
 Energized Neutral
 I returns on gnd (water pipe, etc.)
 Melted neutral or ground insulation
 Uncontrolled I flow

 Three forms
 Loss of Insulation
 High Impedance Connection
 Breaking faults
 Loss of Insulation
 V breakdown of dielectric
 Heat, ejecta, loss of material
 Easily recognized

 High Z connection
 Most common fault
 Misaligned contacts
 Poor connections
 Partially damaged insulation
 Not recognized by standard breakers
 Heat exceeds ignition

 Breaking Faults
 Switching
 Pulling apart cable
 High frequency component
 Sudden increase in voltage
 Causes damage to insulation particularly at high inductance points (bends)

 A failure may not result in immediate catastrophe
 Catastrophic failures are the result of multiple improper conditions.
Seldom do systems have serious consequences when only one component is improper.

 To ensure that all systems
(facility and service) are operating at the same POTENTIAL reference
 To prevent circulating CURRENTS from developing in ground system
 To allow building and service protection systems to operate effectively and as designed in TIME

 Improper grounding and bonding is frequent problem
 Electrical ignition and shock that is
“undetermined” is often grounding
 Codes and standards are minimum requirements. Not following creates hazards
 Grounding issues are code, then legal issues.