THE SUBJECT GROUNDING AND THE NEC THE

THE SUBJECT GROUNDING AND THE NEC

THE SPEAKER • • BOB LUDECKE Member IAEI CA Certified Electrician Lic. Electrical Contractor CSLB Industry Expert CSLB Subject Matter Expert Hands on Electrician Since 1974

SPECIAL THANKS TO Thomas E. Trainor Chief Electrical Inspector City of San Diego, California Representing IAEI on CMP 7 Member - NFPA Member - U. L. Electrical Council

ALSO GUILTY OF: Member of the original NFPA Task Group on the Useability of the National Electrical Code Chaired the sub-committee assigned to review Article 250 and make recommendations to improve it’s “useability”

The ‘ 99 NEC Completely Reorganized Exceptions Minimized And Most Importantly. . . . Performance Requirements Added

Prescriptive vs Performance NEC rules are typically Prescriptive A Prescriptive Rule tells you what to do But, what it doesn’t tell you is. . . Why you’re doing it!

Prescriptive vs Performance A Performance Rule is descriptive It describes what has to be accomplished And this description will most generally Explain the intent of the rule

Why is this Important? Grounding continues to be a Mystery Improper Grounding is Commonplace Proper Grounding is vital for an installation To protect from Fire and Electrocution

Why is this Important? It is my considered opinion, That a better understanding of The intent of the Grounding Rules Will lead to better, safer installations

TYPICAL CIRCUIT OPERATION • Only four things can happen when a circuit is energized. • It can operate normally • There can be an overload • There can be a short circuit • There can be a ground fault

HOW DOES GROUNDING FIT IN? • As long as the circuit is operating normally, • GROUNDING IS NOT NEEDED

THE “UNGROUNDED” CIRCUIT T A circuit consisting of a transformer, 2 - 15 A conductors and a light bulb will operate just fine (Check out the barn) Grounding is not needed To make it work or To make it safe

HOW DOES GROUNDING FIT IN? • Under an overload condition, • GROUNDING IS NOT NEEDED • PROTECTION FROM OVERLOAD IS PROVIDED BY • THE OVERCURRENT DEVICE • Note that current is only flowing on the conductors that we installed to carry current

HOW DOES GROUNDING FIT IN? • Under a short circuit condition, • GROUNDING IS NOT NEEDED • PROTECTION AGAINST SHORT CIRCUIT IS PROVIDED BY • THE OVERCURRENT DEVICE • Again, current is only flowing on the conductors we installed to carry current

HOW DOES GROUNDING FIT IN? • Under a ground fault condition, • GROUNDING IS NOT NEEDED • PROTECTION AGAINST GROUND FAULT IS PROVIDED BY • THE OVERCURRENT DEVICE • HOWEVER……. . .

RETURN PATH REQUIRED • THE OVERCURRENT DEVICE CAN ONLY PROTECT AGAINST A GROUND FAULT IF, • THE CIRCUIT IS INSTALLED SO THAT ALL METAL PARTS ARE BONDED TOGETHER AND TO THE SERVICE NEUTRAL, • WHICH CREATES A LOW RESISTANCE PATH FOR FAULT CURRENT TO RETURN TO THE SOURCE OF SUPPLY

LETS LOOK AT A TYPICAL CIRCUIT L O A D 100’ of Overhead Distribution Line, 25’ of Service Drop, 25’ of Service Entrance Conductor, 100’ of Branch Circuit Conductors

LETS LOOK AT A TYPICAL CIRCUIT L O A D Current flows…. . .

LETS LOOK AT A TYPICAL CIRCUIT L O A D From the transformer to our Service

PATH OF CURRENT FLOW - NORMAL OPERATION L O A D Through the Overcurrent Device to our Load

PATH OF CURRENT FLOW - NORMAL OPERATION L O A D Through the Load returning to the Service

PATH OF CURRENT FLOW - NORMAL OPERATION L O A D And back to the transformer

PATH OF CURRENT FLOW - NORMAL OPERATION L O A D What determines the amount of current that will flow in this circuit?

PATH OF CURRENT FLOW - NORMAL OPERATION L O A D The Total RESISTANCE or IMPEDANCE in the circuit will determine the amount of current that will flow in the circuit

THINGS YOU CAN COUNT ON • OHMS LAW WORKS • We can change the code, or • Hire a different contractor, or • Use romex instead of EMT, but • E = I x R still works

OVERLOAD AND SHORT CIRCUIT CONDITIONS L O A D How is our circuit protected against overload and short circuit?

OVERLOAD AND SHORT CIRCUIT CONDITIONS 15 A Circuit Breaker L O A D THE OVERCURRENT DEVICE PROTECTS THIS CIRCUIT FROM BOTH OVERLOAD AND SHORT CIRCUIT

SUMMARIZING TO THIS POINT CIRCUIT CONDITION PROTECTION PROVIDED BY: GROUNDING? O/C PROT? NORMAL OPERATION NO NO OVERLOAD CONDITION NO YES SHORT CIRCUIT CONDITION NO YES

GROUND FAULT CONDITION So lets talk about a Ground Fault Condition Which certainly sounds like the one condition where Grounding would be important and decide for ourselves whether Grounding Provides Protection for Equipment or Personnel under a Ground Fault Condition

GROUND FAULT CONDITION L O A D What happens if the hot conductor comes into contact with our metal box?

GROUND FAULT CONDITION L O A D And our friend comes along and touches it? IS HE IN JEOPARDY?

GROUND FAULT CONDITION L O A D NO NOT AT ALL AND WHY NOT?

GROUND FAULT CONDITION L O A D Because the transformer we’re looking at IS NOT GROUNDED so there is NO PATH THROUGH EARTH for current to return to the transformer

GROUND FAULT CONDITION L O A D Yes, that was a “Trick” question Sorry about that But the intent was to make a point

THINGS YOU CAN COUNT ON • NO CIRCUIT - NO CURRENT • CURRENT DOES NOT FLOW UNLESS THERE IS A CONTINOUS PATH FROM ONE SIDE OF THE SOURCE OF SUPPLY TO THE OTHER • CURRENT CANNOT TRAVEL THROUGH THE EARTH TO RETURN TO A TRANSFORMER UNLESS THE TRANSFORMER IS GROUNDED

GROUND FAULT CONDITION L O A D So our friend in this situation is perfectly safe HOWEVER. . .

GROUND FAULT CONDITION L O A D What do we know about utility company transformers?

GROUND FAULT CONDITION L O A D THEY’RE GROUNDED And, with this transformer grounded, our friend is in serious jeopardy

SO WHY ARE THEY GROUNDED? • To minimize the damage caused if lightning strikes their distribution lines, or • If a 12 KV line drops onto a low voltage line, • In addition, grounding the neutral of the distribution system stabilizes the voltage. • So, basically for the same reason we ground services at buildings.

GROUND FAULT CONDITION L O A D Because utility transformers are grounded, we need to do something to our equipment to keep our friend from being electrocuted

GROUND FAULT CONDITION L O A D Can we protect our friend by grounding our metal equipment? Lets take a look.

GROUND FAULT CONDITION L O A D Grounding our equipment provides a second path for fault current

GROUND FAULT CONDITION L O A D The first is through our friend to earth and back to the transformer

GROUND FAULT CONDITION L O A D The new second path is through our metal equipment to earth and back to the transformer

FAULT CURRENT PATH We need to open a 15 A Circuit Breaker as quickly as possible. This will require a fault current of 60 A to 75 A. (4 to 5 times the rating of the breaker) We can use Ohm’s Law to find out how much current will flow on our new path.

GROUND FAULT CONDITION L O A D The voltage is 120 V. We need to know the resistance in this circuit to calculate current

FAULT CURRENT PATH Assuming a minimum of 5 ohms resistance through each grounding electrode, we know there is at least 10 ohms resistance in the fault path that we created by grounding our equipment.

FAULT CURRENT PATH THEREFORE, USING OHM’S LAW: E = I x R and Transposing, I = E / R I (current) = E(voltage) / R(resistance) and so, I = 120 / 10 = 12 A

FAULT CURRENT PATH ONLY 12 AMPS WILL 12 AMPS TRIP OUR 15 A CIRCUIT BREAKER? ABSOLUTELY NOT

WITH EQUIPMENT GROUNDED L O A D So the Overcurrent Device does not open And we have fried our friend

CONCLUSION GROUNDING DOES NOT PROTECT EQUIPMENT OR PERSONNEL FROM A GROUND FAULT

THE BONDING CONNECTION L O A D The vital connection left out of our discussion until now is the bonding of metal equipment to the service neutral

THE BONDING CONNECTION Every piece of conductive metal which is a part of our system or likely to become energized Must be connected together by an electrically continuous metal-to-metal contact or by an equipment grounding conductor

THE BONDING CONNECTION These connections create an electrically continuous, low resistance path from every part of our system back to the service equipment At the Service, these connections terminate on the Neutral Bus

THE BONDING CONNECTION L O A D These bonding connections let us use the neutral as a return path for fault current

THE BONDING CONNECTION L O A D Bonding provides a third path for fault current to return to the source of supply

FAULT CURRENT PATH We need to open a 15 A Circuit Breaker as quickly as possible. This will require a fault current of 60 A to 75 A. (4 to 5 times the rating of the breaker) We can use Ohm’s Law to find out how much current will flow on our new path.

FAULT CURRENT PATH The resistance in this path includes 100’ - #2 AL OH Distribution . 032 25’ - #4 AL Service Drop . 013 25’ - #2 CU Service Entrance . 005 100’ - #14 CU Branch Circuit . 307 Resistance to the point of fault . 357 ohms

THE BONDING CONNECTION. 357 ohms . 3 ohms L O A D The resistance from the point of fault through our metal equipment back to the neutral is assumed to be the same as the branch circuit wiring and 100’ of #14 cu has a resistance of. 3 ohm

THE BONDING CONNECTION. 357 ohms . 3 ohms The total resistance in this path created by bonding is. 714 ohms L O A D

FAULT CURRENT PATH USING OHM’S LAW: E = I x R and Transposing, I = E / R I (current) = E(voltage) / R(resistance) and so, I = 120 /. 714 = 168 A

THE BONDING CONNECTION L O A D The Fault Current Return Path through the Neutral allows 168 A of fault current to flow and forces the overcurrent device to open

THE BONDING CONNECTION L O A D THIS PATH DOES NOT RELY ON GROUNDING AND WORKS EVEN IF OUR SYSTEM IS NOT GROUNDED

CONCLUSION THE OVERCURRENT DEVICE PROTECTS AGAINST GROUND FAULT CONDITIONS PROVIDED THAT OUR CIRCUITS HAVE BEEN INSTALLED SO THAT ALL CONDUCTIVE METALS ARE BONDED TOGETHER AND TO THE SERVICE NEUTRAL

IN REVIEW GROUNDING IS A CONNECTION TO EARTH INTENDED TO PROTECT OUR ELECTRICAL SYSTEM FROM LIGHTNING AND HIGH VOLTAGE

IN REVIEW THE OVERCURRENT DEVICE PROTECTS OUR ELECTRICAL SYSTEM FROM OVERLOAD AND SHORT CIRCUIT

IN REVIEW THE OVERCURRENT DEVICE PROTECTS OUR ELECTRICAL SYSTEM FROM A GROUND FAULT CONDITION IF…….

IN REVIEW PROPER BONDING HAS CREATED AN ELECTRICALLY CONTINOUS, LOW RESISTANCE PATH FOR FAULT CURRENT TO RETURN TO THE NEUTRAL AT THE SERVICE

SO WHAT’S THE PROBLEM? WHY DOES “GROUNDING” CONTINUE TO BE A SUBJECT OF MYSTERY AND CONFUSION?

IN MY OPINION There are Three Areas where the CODE has not dealt well with this subject. THEY ARE: CONFUSING VOCABULARY OVER-EMPHASIS ON GROUNDING ACTUAL MISINFORMATION

VOCABULARY WHICH TERMS ARE EASIER TO READ AND UNDERSTAND? un. GROUNDed HOT GROUNDed NEUTRAL GROUNDing GROUND ENOUGH SAID

OVER-EMPHASIS ON GROUNDING ARTICLE 250 IN THE 1996 NEC IS DIVIDED INTO TWELVE PARTS ELEVEN ARE ON GROUNDING ONLY ONE IS ON BONDING The Term “Low Impedance Ground Fault Return Path” is not mentioned at all

ACTUAL MISINFORMATION IN THE 1990 NEC, THE FINE PRINT NOTES TOLD US THAT EQUIPMENT WAS GROUNDED IN ORDER TO “FACILITATE THE OPERATION OF OVERCURRENT DEVICES UNDER FAULT CONDITIONS”

ACTUAL MISINFORMATION IN THE 1996 NEC, SECTION 250 -51 STILL TELLS US THAT THE “PATH TO GROUND” MUST BE OF LOW IMPEDANCE IN ORDER TO “FACILITATE THE OPERATION OF THE CIRCUIT PROTECTIVE DEVICES”

ACTUAL MISINFORMATION ARTICLE 100 PROVIDES GOOD DEFINITIONS OF: GROUNDING, which is A CONNECTION TO EARTH, and BONDING, which is AN INTERCONNECTION OF PARTS

ACTUAL MISINFORMATION BUT ARTICLE 250 HAS TENDED TO USE THE TERM “GROUNDING” AS IF IT INCLUDED THE CONNECTION TO EARTH, THE INTERCONNECTION OF PARTS and THE FAULT CURRENT PATH

THE 1999 NEC BRINGS US……. A RESTRUCTURED AND REVISED ARTICLE 250 Which not only: Puts requirements in a more logical order, And reduces the number of exceptions by changing them to positive text

THE 1999 NEC BRINGS US……. BUT ALSO ADDS: PERFORMANCE REQUIREMENTS FOR GROUNDING and BONDING, AND THE NEW TERM “FAULT CURRENT PATH”

THE 1999 NEC BRINGS US……. AND, THROUGH THESE NEW PERFORMANCE REQUIREMENTS, MORE CLEARLY IDENTIFIES WHAT GROUNDING, BONDING AND THE FAULT CURRENT PATH ARE REQUIRED TO ACCOMPLISH

THE 1999 NEC BRINGS US……. Appendix E which provides cross references from the “ 96 to the ‘ 99 NEC and vice versa Figure 250 -2 which graphically depicts the relationship of Bonding to the other Parts of Article 250 to emphasize it’s importance

HOWEVER. . . AMENDMENTS TO ARTICLE 250 IN THE 1999 NEC HAVE BEEN APPROVED BY CMP-5 AND AT THE NFPA ANNUAL MEETING IN ANAHEIM WE CAN BENEFIT FROM THESE ADOPTED CHANGES WHICH WILL BE PUBLISHED IN THE 2002 NEC

Help From The 2002 NEC In a new Section 250 -2, the 2002 NEC adds definitions of technical terms, such as: Ground Fault Ground-Fault Current Path Effective Ground-Fault Current Path A real help in understanding the intent of the Grounding and Bonding requirements

Help From The 2002 NEC Old Section 250 -2 becomes 250 -4 Which now better explains the differences between Grounding and Bonding, and Separates the requirements for Grounded and Ungrounded Systems Another plus for user-friendly code

THE 2002 NEC New Section 250 -2 Definitions. Ground Fault. An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally noncurrent carrying conductors, metallic enclosures, metallic raceways, metallic equipment or earth.

THE 2002 NEC New Section 250 -2 Definitions. Ground-Fault Current Path. An electrically conductive path from the point of a ground fault on a wiring system through normally non-current carrying conductors, equipment or the earth to the electrical supply source.

THE 2002 NEC New Section 250 -2 Definitions. FPN: Examples of ground-fault current paths could consist of any combination of equipment grounding conductors, metallic raceways, metallic cable sheaths, electrical equipment, and any other electrically conductive material such as metal water and gas piping, steel framing members, stucco mesh, metal ducting, reinforcing steel, shields of communication cables and the earth itself.

THE 2002 NEC New Section 250 -2 Definitions. Effective Ground-Fault Current Path. An intentionally constructed, permanent, low impedance, electrically conductive path designed and intended to carry current under ground fault conditions from the point of a ground fault on a wiring system to the electrical supply source.

THE 2002 NEC New Section 250 -2 Definitions. FPN: An effective ground-fault current path is created by effectively bonding together all of the electrically conductive materials that are likely to be energized by the wiring system. Effective bonding is accomplished through the use of equipment grounding conductors, bonding jumpers or bonding conductors, approved metallic raceways, connectors and couplings, approved metallic sheathed cable and cable fittings, and other approved devices. A ground fault path is effective when it will safely carry the maximum ground fault current likely to be imposed on it.

THE 2002 NEC New Section 250 -2 Definitions. An effective ground-fault current path is created by effectively bonding together all of the electrically conductive materials that are likely to be energized by the wiring system.

THE 2002 NEC New Section 250 -2 Definitions. Effective bonding is accomplished through the use of equipment grounding conductors, bonding jumpers or bonding conductors, approved metallic raceways, connectors and couplings, approved metallic sheathed cable and cable fittings, and other approved devices.

THE 2002 NEC New Section 250 -2 Definitions. A ground fault path is effective when it will safely carry the maximum ground fault current likely to be imposed on it.

Help From The 2002 NEC Old Section 250 -2 becomes: 250 -4. General Requirements for Grounding and Bonding which is divided into: (A) Grounded Systems, and (B) Ungrounded Systems

Help From The 2002 NEC New Section 250 -4 (A) (1) Electrical System Grounding (2) Grounding of Electrical Equipment (3) Bonding of Electrical Equipment (4) Bonding of Electrically Conductive Materials and Other Equipment (5) Effective Ground Fault Current Path

Help From The 2002 NEC New Section 250 -4 (A) (1) Electrical System Grounding Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and that will stabilize the voltage to earth during normal operation.

Help From The 2002 NEC New Section 250 -4 (A) (2) Grounding of Electrical Equipment Non-current carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

Help From The 2002 NEC New Section 250 -4 (A) (3) Bonding of Electrical Equipment Non-current carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground fault current path.

Help From The 2002 NEC New Section 250 -4 (A) (4) Bonding of Electrical Conductive Materials and Other Equipment Electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground fault current path.

Help From The 2002 NEC New Section 250 -4 (A) (5) Effective Ground Fault Current Path Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low impedance circuit capable of safely carrying the maximum ground fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be used as the sole equipment grounding conductor or fault current path.

Help From The 2002 NEC New Section 250 -4 (B) (1) Grounding of Electrical Equipment (2) Bonding of Electrical Equipment (3) Bonding of Electrically Conductive Materials and Other Equipment (4) Path for Fault Current

Help From The 2002 NEC New Section 250 -4 (B) (1) Grounding of Electrical Equipment Non-current carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and limit the voltage to ground on these materials

Help From The 2002 NEC New Section 250 -4 (B) (2) Bonding of Electrical Equipment Non-current carrying conductive materials enclosing electrical conductors or equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a permanent, low impedance path for ground fault current which is capable of safely carrying the maximum fault current likely to be imposed on it.

Help From The 2002 NEC New Section 250 -4 (B) (3) Bonding of Electrical Conductive Materials and Other Equipment Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a permanent, low impedance path for ground fault current which is capable of safely carrying the maximum fault current likely to be imposed on it.

Help From The 2002 NEC New Section 250 -4 (B) (4) Path for Fault Current Electrical equipment, wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a second fault occur on the wiring system. The earth shall not be used as the sole equipment grounding conductor or fault current path.

IN CLOSING THE CHANGES TO ARTICLE 250 IN THE ‘ 99 & ‘O 2 NEC ARE EXTENSIVE IT HAS BEEN COMPLETELY RENUMBERED AND REWORDED MANY EXCEPTIONS HAVE BEEN REWRITTEN INTO POSITIVE TEXT

IN CLOSING SOME RULES, SUCH AS 250 -32, HAVE BEEN COMPLETELY CHANGED OTHERS HAVE BEEN RELOCATED, REWRITTEN AND/OR REORGANIZED THESE CHANGES WILL AFFECT EVERYONE INVOLVED IN THE ELECTRICAL INDUSTTRY

THE POSITIVE APPROACH These changes are a blessing in disguise We all need to get a fresh start on this subject and clarify our understanding of why we ground and bond electrical systems and how grounding and bonding are related to safe electrical installations

THE POSITIVE APPROACH The best way to do that is to work through Article 250 as if it were totally new Check that terms are used consistently as they are defined Check the rules against what you see in the field

THE POSITIVE APPROACH Always question the “why” of the rule Don’t stop until you really understand it And how to apply it on the job

THE POSITIVE APPROACH And, when you review Grounding Use the wording in the 2002 NEC It’s the closest we’ve ever gotten to accurately describing this topic

THE POSITIVE APPROACH Using the new wording in the 2002 NEC Will make it easier to show contractors what Grounding and Bonding have to accomplish And that’s important because

THE POSITIVE APPROACH Grounding Bonding and the Ground-Fault Current Path are critical elements of electrical safety

THANK YOU FOR YOUR TIME AND ATTENTION