1. Grounding, bonding, and ground fault currents
Why all the confusion?

2. Why learn about Grounding?
Grounding continues to be a Mystery
Improper Grounding is Commonplace
Proper Grounding is vital for a proper installation
To protect from fire, shock, & even death

3. 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

4. HOW DOES GROUNDING FIT IN?
As long as the circuit is operating NORMALLY
GROUNDING IS NOT NEEDED

5. THE “UNGROUNDED” CIRCUIT
A circuit consisting of a transformer, two 14 AWG wires 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

6. SO, HOW DOES GROUNDING FIT IN?
Under an overload situation
Grounding is not needed
Protection from the overload is provided by the Over Current Device (circuit breaker)
Note that current is only flowing on the conductors that we installed to carry the current

7. Under a short circuit situation
Grounding is not needed
Again, protection from the short circuit is provided by the Over Current Device
Again, the current is only flowing on the conductors that we installed to carry the current

8. However Under a ground fault situation Grounding is not needed
Once again, protection from the ground fault is provided by the Over Current Device
However

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

10. LETS LOOK AT A TYPICAL CIRCUITD
100’ of Overhead Distribution Line,
25’ of Service Drop,
25’ of Service Entrance Conductor,
100’ of Branch Circuit Conductors

11. L O A D
Current flows…...

12. From the transformer to our ServiceL O A D
From the transformer to our Service

13. Through the Over Current Device to our Load
THIS WOULD BE THE PATH OF CURRENT FLOW UNDER NORMAL OPERATION L O A D
Through the Over Current Device to our Load

14. Through the Load returning to the Service

15. And back to the transformerL O A D
And back to the transformer

16. What determines the amount of current that will flow in this circuit?

17. L O A D
The Total RESISTANCE or IMPEDANCE in the circuit will determine the amount of current that will flow in the circuit

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

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

20. OVERLOAD AND SHORT CIRCUIT CONDITIONS
15A Circuit Breaker L O A D
THE OVER CURRENT DEVICE
PROTECTS THIS CIRCUIT FROM BOTH
OVERLOAD AND SHORT CIRCUIT

21. PROTECTION PROVIDED BY:
SUMMARY
CIRCUIT CONDITION
PROTECTION PROVIDED BY:
Grounding?
Cir Breaker
NORMAL OPERATION NO NO
OVERLOAD CONDITION NO
YES
SHORT CIRCUIT CONDITION NO
YES
GROUND FAULT CONDITION
Let’s talk

22. THE 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

23. GROUND FAULT CONDITION
What happens if the hot conductor comes into contact with our metal box?

24. GROUND FAULT CONDITION
And our friend comes along and touches it?
IS HE IN JEOPARDY?

25. GROUND FAULT CONDITIONNO
NOT AT ALL
AND WHY NOT?

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

27. GROUND FAULT CONDITION
Yes, that was a “Trick” question
Sorry about that
But the intent was to make a point

28. No Circuit - No Current
CURRENT DOES NOT FLOW UNLESS THERE IS A CONTINUOUS 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

29. GROUND FAULT CONDITION
So our friend in this situation is perfectly safe
HOWEVER.....

30. GROUND FAULT CONDITION
What do we know about utility company transformers?

31. GROUND FAULT CONDITION
THEY’RE GROUNDED
And, with this transformer grounded, our friend is in serious jeopardy

32. Why are Transformers 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.

33. GROUND FAULT CONDITION
Because utility transformers are grounded, we need to do something to our equipment to keep our friend from being shocked or electrocuted.

34. GROUND FAULT CONDITION
Can we protect our friend by grounding our metal equipment? Lets take a look.

35. GROUND FAULT CONDITION
Grounding our equipment provides a second path for fault current

36. GROUND FAULT CONDITION
The first is through our friend to earth and back to the transformer

37. GROUND FAULT CONDITION
The new second path is through our metal equipment to earth and back to the transformer

38. We need to open a 15A Circuit Breaker as quickly as possible
We need to open a 15A Circuit Breaker as quickly as possible. This will require a fault current of 60A to 75A (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.

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

40. 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.

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

42. WILL 12 AMPS TRIP OUR 15A CIRCUIT BREAKER?
ONLY 12
AMPS
ABSOLUTELY NOT
WILL 12 AMPS TRIP OUR 15A CIRCUIT BREAKER?

43. WITH EQUIPMENT GROUNDEDL O A D
So the Overcurrent Device does not open
And we have fried our friend

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

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

46. 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

47. 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

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

49. THE BONDING CONNECTIONL O A D
Bonding provides a third path for fault current to return to the source of supply

50. We need to open a 15A Circuit Breaker as quickly as possible
We need to open a 15A Circuit Breaker as quickly as possible. This will require a fault current of 60A to 75A (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.

51. 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

52. THE BONDING CONNECTION
.357 ohms L O A D
.3 ohms
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

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

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

55. THE BONDING CONNECTIONL O A D
The Fault Current Return Path through the Neutral allows 168A of fault current to flow and forces the Over Current device to open

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

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

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

59. THE OVERCURRENT DEVICE
PROTECTS OUR ELECTRICAL SYSTEM
FROM OVERLOAD AND SHORT CIRCUIT

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

61. PROPER BONDING HAS CREATED
AN ELECTRICALLY CONTINUOUS,
LOW RESISTANCE PATH
FOR FAULT CURRENT TO RETURN
TO THE NEUTRAL AT THE SERVICE

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

63. Grounding, Bonding and the Ground-Fault Current Path are critical elements of electrical safety

64. THANK YOU