Ignition or Shock

1
Ignition or Shock

• Is Grounding the Culprit

Marcus O. Durham, PhD, PE Robert A. Durham, PhD,
PE ThewayCorp.com
2
Why Ground ?

• 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?

3
Grounding

• Complex Topic
• Critical for electrical safety
• Biologic
• Property
• NEC - gt 28 pages
• NESC Specific Requirements
• IEEE Multiple Standards
• NFPA Myriad Publications

4
Significance

• 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

5
Grounding System

• Three components
• Grounding Electrode
• Contact point with earth
• NEC lt25? or additional electrode required
• NESC - lt 25?.
• IEEE 142 - 25? not satisfactory 1-5?
• Grounding Electrode Conductor
• Connects grounding electrode to system
• Must handle fault currents NEC size

6
Grounding system

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

7
Neutral

• Current carrying conductor
• Controlled return path for 1F DC
• Single point connection to ground
• If multiple points
• current flows through grounding system
• If poor connection
• circuit current can flow
• through ground

8
Stray Current

• 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

9
Multi Point Neutral

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

In
10
Transients

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

11
Transients - Lightning

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

12
Energization Issues

• 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

13
Energization Issues

• 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

14
Faults

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

15
Faults

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

16
Faults

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

17
Why Fail Now?

• 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.
18
Grounding Purpose

• 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

19
Recap

• 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.

20
Questions?