Presentation on theme: "Grounding & Bonding A Short story by The Electrical Guru TM Paul W. Abernathy,CME NACHI Electrical Educator NEC Consultant/Speaker Images provided by Mike."— Presentation transcript:
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 its creation. It will use the earth as a PATH if needed but only that.
Even More Grounding……. OK…lets 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 its 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 its 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. So like in THIS panel..lets keep the Grounded and Grounding bars APART ! Isolated Grounded Conductor
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. Notice the LOOSE grounded ( neutral ) connection below….
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 Holts Books. This was designed as a BRIEF lesson for the Home Inspection Industry by The Electrical Guru www.TheElectricalGuru.com