1 / 20

Ignition or Shock

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

truly
Download Presentation

Ignition or Shock

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Is Grounding the Culprit Ignition or Shock 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 - > 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 <25Ω or additional electrode required • NESC - < 25Ω. • IEEE 142 - 25Ω not satisfactory – 1-5Ω • 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 1Φ & 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?

More Related