G R O U N D I N G AND THE N E C THE SUBJECT

THE
N E C

THE SUBJECT

Subject Matter Expert
Hands on Electrician Since 1974

City of San Diego, California
Representing

SPECIAL THANKS TO

Chaired the sub-committee assigned to review Article 250 and make recommendations to improve it’s “useability”

ALSO GUILTY OF:

tells you what to do
But, what it doesn’t tell you

Why you’re doing it!

has to be accomplished
And this description will most generally
Explain the

Grounding is vital for an installation
To protect from Fire

Improper Grounding is Commonplace

of the Grounding Rules
Will lead to better, safer installations

That a better understanding of

is energized.
It can operate normally
There can be an overload
There can

is operating normally,

GROUNDING IS NOT NEEDED

As long as the circuit

conductors and a light bulb will operate just fine

THE “UNGROUNDED” CIRCUIT

To make it work

or To make it safe

NEEDED

PROTECTION FROM OVERLOAD

NOT NEEDED

PROTECTION AGAINST SHORT CIRCUIT IS PROVIDED BY
THE OVERCURRENT

NOT NEEDED

PROTECTION AGAINST GROUND FAULT IS PROVIDED BY
THE OVERCURRENT

GROUND FAULT IF,
THE CIRCUIT IS INSTALLED SO THAT ALL

LETS LOOK AT A TYPICAL CIRCUIT
100’ of Overhead Distribution

LETS LOOK AT A TYPICAL CIRCUIT
Current flows…...

LETS LOOK AT A TYPICAL CIRCUIT
From the transformer to

PATH OF CURRENT FLOW - NORMAL OPERATION
Through the

PATH OF CURRENT FLOW - NORMAL OPERATION
Through the

transformer
L
O
A
D

of current that will flow in this circuit?
L
O

IMPEDANCE in the circuit will determine the amount of current

L
O
A
D

can change the code, or
Hire a different contractor, or
Use romex

overload and short circuit?
L
O
A
D

BOTH
OVERLOAD AND SHORT CIRCUIT
15A Circuit Breaker
L
O
A

CIRCUIT CONDITION
NO
YES

like the one condition where Grounding would be important and

Grounding Provides Protection for Equipment or Personnel under a Ground Fault Condition

GROUND FAULT CONDITION

contact with our metal box?
L
O
A
D

GROUND FAULT CONDITION
And our friend comes along and touches

D

L
O
A
D

the intent was to make a point
L
O

- NO CURRENT

CURRENT DOES NOT FLOW UNLESS THERE IS

safe
HOWEVER.....
L
O
A
D

L
O
A
D

L
O
A
D

lightning strikes their distribution lines, or
If a 12 KV line

do something to our equipment to keep our friend from

L
O
A
D

metal equipment? Lets take a look.
L
O
A
D

fault current
L
O
A
D

GROUND FAULT CONDITION
The first is through our friend to

GROUND FAULT CONDITION
The new second path is through our

as possible. This will require a fault current of 60A

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 circuit to calculate current
L
O

electrode, we know there is at least 10 ohms resistance

FAULT CURRENT PATH

and Transposing, I = E / R
I (current) =

and so, I = 120 / 10 = 12A

AMPS TRIP

ABSOLUTELY NOT

So the Overcurrent Device does not

And we have fried our friend

until now is the bonding of metal equipment to the

L
O
A
D

our system or likely to become energized
Must be connected

THE BONDING CONNECTION

path from every part of our system back to the

At the Service, these connections terminate on the Neutral Bus

the neutral as a return path for

L
O
A
D

to return to the source of supply
L
O
A

as possible. This will require a fault current of 60A

We can use Ohm’s Law to find out how much current will flow on our new path.

FAULT CURRENT PATH

100’ - #2 AL OH Distribution .032
25’ - #4 AL

FAULT CURRENT PATH

.357 ohms

.3 ohms

.357 ohms
.3 ohms
.57 ohms
The total resistance in

and Transposing, I = E / R
I (current) = E(voltage)

and so, I = 120 / .714 = 168A

the Neutral allows 168A of fault current to

L
O
A
D

WORKS EVEN IF
OUR SYSTEM IS NOT GROUNDED

OUR CIRCUITS HAVE BEEN INSTALLED SO THAT ALL CONDUCTIVE METALS

SYSTEM FROM
LIGHTNING AND HIGH VOLTAGE

SHORT CIRCUIT

FAULT CONDITION
IF…….

FOR FAULT CURRENT TO RETURN
TO THE NEUTRAL AT THE SERVICE

SUBJECT OF
MYSTERY AND CONFUSION?

not dealt well with this subject.
THEY ARE:
CONFUSING VOCABULARY
OVER-EMPHASIS ON GROUNDING
ACTUAL

IS DIVIDED INTO TWELVE PARTS
ELEVEN ARE ON GROUNDING
ONLY ONE IS

The Term “Low Impedance Ground Fault Return Path” is not mentioned at all

US THAT EQUIPMENT WAS GROUNDED IN ORDER TO
“FACILITATE THE OPERATION

THE
“PATH TO GROUND” MUST BE OF LOW IMPEDANCE IN

ACTUAL MISINFORMATION

TO EARTH, and
BONDING, which is
AN INTERCONNECTION OF PARTS
ACTUAL MISINFORMATION

AS IF IT INCLUDED
THE CONNECTION TO EARTH,
THE INTERCONNECTION

ACTUAL MISINFORMATION

not only:
Puts requirements in a more logical order,
And reduces

and BONDING,
AND THE NEW TERM
“FAULT CURRENT PATH”

CLEARLY IDENTIFIES WHAT GROUNDING, BONDING AND

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

APPROVED BY CMP-5 AND AT THE NFPA ANNUAL MEETING IN

WE CAN BENEFIT FROM THESE ADOPTED CHANGES WHICH WILL BE PUBLISHED IN THE 2002 NEC

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

now better explains the differences between Grounding and Bonding, and
Separates

Another plus for user-friendly code

unintentional, electrically conducting connection between an ungrounded conductor of an

An electrically conductive path from the point of a ground

ground-fault current paths could consist of any combination of equipment

Path.
An intentionally constructed, permanent, low impedance, electrically conductive path

ground-fault current path is created by effectively bonding together all

current path is created by effectively bonding together all of

accomplished through
the use of equipment grounding conductors, bonding jumpers

path is effective when it will safely carry the maximum

Requirements for Grounding and Bonding
which is divided into:
(A) Grounded Systems,

(B) Ungrounded Systems

Electrical System Grounding
(2) Grounding of Electrical Equipment
(3) Bonding of Electrical

(4) Bonding of Electrically Conductive Materials and Other Equipment

(5) Effective Ground Fault Current Path

Electrical System Grounding
Electrical systems that are grounded shall be connected

Section 250-4 (A)
(2) Grounding of Electrical Equipment
Non-current carrying conductive materials

Bonding of Electrical Equipment
Non-current carrying conductive materials enclosing electrical conductors

Bonding of Electrical Conductive Materials and Other Equipment
Electrically conductive materials

Effective Ground Fault Current Path
Electrical equipment and wiring and

Grounding of Electrical Equipment
(2) Bonding of Electrical Equipment
(3) Bonding

(4) Path for Fault Current

Grounding of Electrical Equipment
Non-current carrying conductive materials enclosing electrical conductors

Bonding of Electrical Equipment
Non-current carrying conductive materials enclosing electrical conductors

Bonding of Electrical Conductive Materials and Other Equipment
Electrically conductive materials

Path for Fault Current
Electrical equipment, wiring and other electrically

‘O2 NEC ARE EXTENSIVE
IT HAS BEEN COMPLETELY RENUMBERED AND REWORDED
MANY

HAVE BEEN RELOCATED, REWRITTEN AND/OR REORGANIZED
THESE CHANGES WILL AFFECT EVERYONE

need to get a fresh start on this subject and

work through Article 250 as if it were totally new
Check

Check the rules against what you see in the field

until you really understand it
And how to apply it

the 2002 NEC
It’s the closest we’ve ever gotten to

make it easier to show contractors what Grounding and Bonding

And that’s important because

Bonding
and the