Transcript Grounding & Bonding

Grounding & Bonding
A “Short” story by
The Electrical Guru
Paul W. Abernathy,CME
NACHI Electrical Educator
NEC Consultant/Speaker
Images provided by Mike Holt Enterprises,Inc.
TM
Grounding…………..
The easiest way to understand grounding
is that in the electrical system all
connections made from the system to
the earth is considered “grounding”
and serves this main purpose.
High-voltage system windings are grounded to
the earth to help limit high voltage imposed
on the system windings from lightning,
unintentional contact with higher-voltage
lines, or line surges.
Grounding Electrical Equipment to the Earth.
Metal parts of electrical equipment must be
grounded to the earth by electrically
connecting the building or structure
disconnecting means with a grounding
electrode conductor to a grounding
electrode
More Grounding……….
Now as you can see when we
are dealing with the
“Grounding” issue you will
find many possible
connections as shown on the
right but the common
understanding is that they all
make a connection to
GROUND or EARTH !
So basically lets understand that
the connection from
enclosures to the EARTH is
called grounding for a simple
understanding…lets move on.
Myth# 1: Electricity is trying to get to the
earth….WRONG, Electricity is always trying to
get back to the source of it’s creation . It will use
the earth as a PATH if needed but only that.
Even More Grounding…….
• OK…let’s RECAP….the
Grounding of the
Electrical System to the
EARTH is for lightning &
Line Surge issues and to
aid the utility company. It
will NEVER aid in
clearing a breaker or fuse
at the actual dwelling.
Now lets see WHY!!!!
Yet More Grounding…..
• Ok lets do some OHMS LAW….
• Typical ground rod is assumed to
have 25 OHMS or less which is
pushing it a bit but guess it’s
possible.
Ok….120V source and 25 OHMS of
resistance/impedance….
120V divided by 25 Ohms is =
A MASSIVE 4.8 AMPS
So do you think that will clear a 15
AMP breaker?????????
NOT GONNA HAPPEN
Ok…Now Bonding…….
• What is Bonding Basically?
• To remove dangerous voltage on
metal parts from a ground fault,
electrically conductive metal water
piping systems, metal sprinkler
piping, metal gas piping, and other
metal piping systems, as well as
exposed structural steel members
that are likely to become
energized, must be bonded to an
effective ground-fault current path
[250.4(A)(4)].
• Also important to remember the
important role electrical metallic
conduit serves as well for
bonding….this is NOT grounding !
Yet More Bonding…..
• Ok I hear everyone now saying…Why
do they call the bare wire in a NM
Cable the “ Equipment Grounding
Conductor” when it is really the
Bonding conductor….good
question….lol
What is important to understand with
bonding is that proper bonding of
metal piping and conduit within the
structure offers a low impedance fault
current path BACK to the source in
the event it becomes energized
allowing the breaker or fuse to
function properly.
Without this PATH what can you guess
would happen to the metal that is
energized….Yep..Shocking !
Now lets go DEEPER !!!!
• Now that you basically
understand what grounding
and bonding is for….lets
examine how a “SUB” panel
can be deadly if done
incorrectly.
•
Preventing Objectionable Current.
To prevent a fire, electric shock, or
improper operation of circuitprotection devices or sensitive
equipment, electrical systems and
equipment must be installed in a
manner that prevents objectionable
current from flowing on conductive
materials, electrical equipment, or
grounding and bonding paths.
Lets EXAMINE THIS….
• Notice that IF someone improperly
connects the grounded and grounding
buss bar incorrectly on a “SUB” panel
you have current traveling on the
enclosure and guess what happens if the
grounded ( neutral) conductor comes
loose….the enclosure and the grounding
conductor (equipment grounding
conductor) will carry this current
making for a deadly combination.
• Important note is that guess what
“SUB” panel appears no where in the
National Electrical Code. The proper
term for it is “Remote Distribution
Panel”….technically speaking.
Myth # 2: Electricity takes the path of least
resistance…WRONG, it takes all available
paths proportionally to the source of it’s
creation.
Now we understand it..RIGHT?
•
Improper Neutral-to-Case Bond
[250.142]
Panelboards. Objectionable current
will flow on metal parts when the
grounded neutral conductor is
bonded to the metal case of a
panelboard that is not part of
service equipment. Ie: “SUB” panels
Disconnects. Objectionable current
will flow on metal parts when the
grounded neutral conductor is
bonded to the metal case of a
disconnecting means that is not part
of service equipment.
•
YEP…..that is WHY “remote” panels
should not have their GROUNDED
conductor bonding to the metal
enclosure.
Isolated
Grounded
Conductor
So like in THIS
panel..lets keep
the Grounded
and Grounding
bars APART !
Notice the LOOSE grounded ( neutral )
connection below….
Summary……
•
We have established some basics.
GROUNDING is the connection to earth
and BONDING is connection of metal
parts to provide a low impedance path for
fault current to aid in clearing the
overcurrent protection device and to
remove dangerous current from metal that
is likely to become energized.
•
Improper Operation of Circuit-Protection
Devices. When objectionable current travels
on the metal parts of electrical equipment,
nuisance tripping of electronic protection
devices equipped with ground-fault
protection can occur because some neutral
current flows on the equipment grounding
(bonding) conductor instead of the
grounded neutral conductor.
Thank You……..
•
•
Now obviously I was not able to
cover ALL the issues and concerns
regarding Grounding and Bonding
and I am sure critics will point that
out. The intent of this video was to
explain the basics of the subject
and not to be a conclusive lesson
on every aspect. If you would like
to learn MORE about this subject
check out Mike Holt’s Books.
This was designed as a BRIEF
lesson for the Home Inspection
Industry by
“ The Electrical Guru”
www.TheElectricalGuru.com