Grounding & Bonding by 3257j7P

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									                  Grounding & Bonding

                                       A “Short” story by

                 The Electrical Guru                                        TM



                                      Paul W. Abernathy,CME
                                                NACHI Electrical Educator
                                                 NEC Consultant/Speaker


Images provided by Mike Holt Enterprises,Inc.
                      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 circuit-
    protection 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
                                                              Isolated
    grounded neutral conductor is                             Grounded
    bonded to the metal case of a                             Conductor
    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          So like in THIS
    bonded to the metal case of a          panel..lets keep
    disconnecting means that is not part   the Grounded
                                           and Grounding
    of service equipment.                  bars APART !

•   YEP…..that is WHY “remote” panels
    should not have their GROUNDED
    conductor bonding to the metal
    enclosure.
                                                  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

								
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