Case histories of ground system failures, loss of electrical power, electrical shocks
Class on how to inspect electrical panels, home inspection procedures and safety
Questions & answers about how to inspect residiential electrical wiring ground system, & about defects in electrical ground system wiring
Electrical ground system inspection: this document discusses procedures the inspection of the grounding system components of a building electrical system when performed by trained building inspection professionals, home inspectors, electrical inspectors, and electricians.
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Guide to Inspecting Electrical Service Grounding Equipment for Defects
While we have frequently updated and added to the material, in its original form this information was presented by
Daniel Friedman - InspectAPedia.com, at the Hudson Valley chapter of the American Society of Home Inspectors -
HVASHI Seminar 12 Sept 2002, Updated April 2006.
“Grounding”, article 250 in the NEC, is probably one of the most difficult of the often used articles. In 2005 article 250 became “Grounding and bonding”. In the 2008 NEC there has been a major revision in language, and phrases like “shall be grounded” have changed to “shall be connected to an equipment grounding conductor.” Here we define electrical ground, grounding, bonding, and earthing terms and explain why there are important differences among these words.
Why we need electrical grounding
The grounding system at a building provides an easy path for electricity to flow to earth should a problem, such as a short circuit, occur. Allowing current to flow to earth through the ground system helps assure that a circuit breaker will trip or fuse will blow should a problem occur. Properly operating these overcurrent devices help prevent fire and shock.
Should an electrical fault occur where no ground path is present, the electrical potential is just sitting there waiting for a person to come along, touch some component of the system, and by accidentally providing a path to earth through their body, receive a burn or potentially fatal shock.
Details of why we need grounding, and definitions of electrical grounding and electrical bonding (what's the difference between these two terms) can be read at Why Grounding is Needed.
Bud, a master electrician from Minnesota has offered these important clarifications:
"Grounding" has 2 main functions.
One is to provide a path to trip a breaker in the event of a 'short'
as in the text above. That function relies on a "ground"-to-neutral
connection required at services in the US (the "main bonding jumper").
The path is (branch circuit ground wire) to (N-G bond at the service)
to (service neutral) to (utility power transformer). This path *must*
be metallic back to the power transformer to provide low resistance to
trip a circuit breaker. This function will work even if the service is
not connected to earth. And the NEC *does not allow* earth to be used
as part of this path.
One reason is the resistance of an earth path is too high. Assume the
earthing is only through a ground rod and the rod has a quite good 10
ohms resistance to earth. Further assume there is a 'short' connecting
hot to "ground". The current to earth will be 12A. There is a good
chance this won't even trip a 15A circuit breaker. If the circuit is
loaded the breaker will trip, but after a significant time delay. In
the mean time, the "ground" potential with respect to the earth away
from the ground rod will be 120V.
Note that if you are using the earth as in the quote above, the path
is not just into the earth. It is back to the power source, and also
depends on the earth connection at the power transformer.
This would be better termed a *bonding* function.
Carson Dunlop's sketch shows how the electrical current in a building can find its way to earth by way of the electrical grounding system. But as you may want to read in our case study of loss of all ground connections at a building, don't assume that the current will always find its way to earth.
Loss of electrical ground at a building is extremely dangerous and risks electrocution.
Some discussion points about electrical grounding are listed just below.
Required for safety, lets fuses blow
Example: toaster falls into metal sink
Grounding Electrode Conductor wire from service equipment to
House plumbing (grounds the plumbing)
Entering metal water pipe (grounds the system)
Grounding Electrode (two now recommended)
Continuous, no splices, meter bypass
Copper ground wires and grounding conductor (corrosion resistant)
Aluminum - bare vs. insulated (risk of corrosion, break in wire, loss of safe grounding - illustrated below)
Gas Piping May Need to Be Bonded to the Electrical Ground System
In some communities, as Carson Dunlop's sketch shows, the metal gas piping in a building must be bonded to the electrical ground system.
Bonding anything to the ground system, including metal gas piping, helps prevent an electrical spark that might otherwise result in an explosion in the case of a gas piping system.
The bonding of the gas piping to the building ground system is not the same thing as attempting to use the metal gas piping as the primary or only connection to earth in a building.
What is Meant by the "Grounding Equipment " in a Building?
As Carson Dunlop's sketch shows, the grounding equipment includes wires which bond the ground and neutral bus in the main electrical panel with an outdoor component that conducts electricity to the earth (ground).
The outdoor component may be grounding electrodes (ground rods), or in some jurisdictions a metal water pipe or possibly other metal components.
Where do Ground Wires Go?
As Carson Dunlop's sketch shows here, from the main electrical panel a grounding conductor connects to:
a pair of grounding electrodes,
a metal water pipe entering the building from outside,
a strip footing which contains metal in contact with the earth
At ALUMINUM GROUND WIRES we discuss proper repair of aluminum ground wires found in solid conductor branch circuit wiring.
Electrical Service Grounding Defects & Conditions to Check For During an Electrical Inspection
What Defects Should We Check for in an Electrical Grounding System?
Jumper wires to ground plumbing: As Carson Dunlop's sketch shows at (A), if the building plumbing includes dialectic fittings or non-conductive sections of piping (such as plastic piping) then the building plumbing system may not be safely grounded.
A jumper wire is installed to assure that the building metal plumbing pipes are safely grounded to earth.
The purpose of the ground jumper is to ground the building plumbing, not to use the building plumbing as a grounding system.
That is to say, we're making the plumbing safe, we're not using it to provide a ground for the electrical system.
Grounding system jumper wire around the water meter: as the same sketch shows at (B), if the building water main piping is being used as a source to provide a ground for the electrical system, then the main ground wire between the electrical panel and the water piping should be clamped on both sides of the water meter.
In this case the building water supply piping is being used as part of the electrical grounding system, and we need to be sure that that connection to earth is not interrupted by non-conductive components of the water meter itself.
In our photo you can see that the meter bypass jumper has become disconnected (where our flashlight is shining) and that the system ground wire was also spliced.
We bond the building water pipe to the grounding wire on the street side of the water meter to be sure that the building electrical system is grounded to earth.
We bond the building water pipe to the grounding wire on the building-side of the water meter to be sure that the building water piping is safely grounded too.
This grounding wire should be continuous, through both pipe clamps securing it to the water piping before and after the water meter, and continuing into the main electrical panel where it joins the ground bus and neutral bus.
Corroded copper grounding wires can also be unreliable as our photo shows.
We would be reluctant to trust this connection for the building grounding system.
List of Additional Electrical Grounding System Checkpoints:
Confirm that a grounding connection to earth is present: New electrical installations should have two grounding electrodes at the building; older homes may have only one grounding electrode, or no ground rods but a connection to an incoming water pipe, or in the worst case, no local ground at all.
You may have to look closely even to find the grounding electrode, but following the ground wire should lead to it if an electrode is present. Photo courtesy of Tim Hemm.
Confirm that grounding is present in all sub panels: Check for grounding not found in sub panel feeder cable
Follow building piping to be sure that its ground path is electrically continuous. A main ground wire attached to plastic pipe is completely ineffective.
Corroded aluminum electrical ground wire - aluminum ground wires corrode through and ground can be lost. That's why new electrical work that uses aluminum ground wires should be performed only using wires that are insulated.
We've seen this happen, as shown in our picture at left, leading to loss of the local building ground connection when the bare aluminum ground wire was touching the edge of a masonry block foundation.
Moisture in the foundation wall and probably the chemistry of the masonry block, mineral salts left by water entry, and the aluminum wire itself led to through-corrosion of the ground wire.
At ALUMINUM GROUND WIRES we discuss proper repair of aluminum ground wires found in solid conductor branch circuit wiring.
Loose or missing ground connections securing the ground wire to a water pipe or to a grounding electrode.
As you can see in our photo, someone just skipped the clamp intended to secure the copper ground wire to the incoming water pipe, and left it wrapped around the pipe quite loosely.
Often we find this condition when someone needed to temporarily disconnect the ground wire, perhaps during a plumbing repair.
The plumber may not have taken seriously the need to re-connect the building ground system.
No one may notice this problem because even if this ground connection is totally ineffective, the building may be still grounded through the service entry ground wire. As we demonstrated at Case History: Double Fault Leads to Loss of Power, it's not safe to rely on just the utility company's ground connection.
False Grounds - are wiring "tricks" that can make an electrical circuit appear to be properly grounded when it is not. A conventional plug-in circuit tester will not find false grounds, as we explain at False Ground at Receptacles where we provide details.
False Neutrals - are wiring "tricks" that make an electrical circuit appear to have a good neutral wire connection when it does not. Since the ground wire or ground path may have been (improperly) used for this, we illustrate an example of a false neutral using a ground path just below, and we discuss this foul-up in detail at False Neutral Connections
The ground system wiring is for emergency-use only - it should never be wired so as to carry current during normal operation. (E.g. This occurs if a
sub panel bonds the neutral to ground wires).
We've found cases in which someone used the ground path to complete an electrical circuit because the neutral wire was broken somewhere that could not be found. As a result, the ground path was electrically live when it should not have been, leading to an electric shock.
In our photo at left, someone used telephone wire to connect the neutral side of this electrical receptacle to the receptacle's steel mounting strap, knowing that that would in turn connect the neutral side of the receptacle to the steel junction box and through it, to the armored BX electrical cable, forming an electrical path back to the main electric panel. We discuss this crazy wiring in more detail at False Neutral Connections.
Indeed this got the receptacle "working" by using the ground path in the system after the original neutral path had been lost.
We were working on renovating the home where we found this condition. How did we find it? We were replacing two-prong un-grounded receptacles with grounded devices. We turned off electrical power to this circuit and began working on it. When our assistant plugged in and began using a vacuum cleaner in the same room we got an electrical surprise - a shock while touching the BX cable!
Grounding Electrode Cut Off, Short, or Inadequate - see below
Ground rod cut off or short - don't assume that because you see a grounding electrode that it has been properly installed. If the installer hit rock and couldn't drive the rod fully into the soil s/he may have cheated and simply cut off the top of the rod. Grounding electrodes in some locales have an embossed code on their upper end - if the rod was cut off the embossed letters will be missing. If a grounding electrode cannot be fully driven into the soil the electrical code provides procedures for driving the electrode in cut-sections to achieve sufficient total earth contact.
As we and our inspection client discovered (photos above), the bent-over grounding electrode made us wonder what was happening. When the grounding electrode was just nudged with a toe, it fell over. Our client was kind enough to demonstrate just how ineffective this electrical ground system was, thanks to someone's shortcut.
Grounding wire not found in main electrical panel
Grounding wire not found in sub panel feeder
Inaccessible connections to the grounding system (can't be inspected or maintained)
Main electrical panel enclosure not bonded to grounding system
Main ground wire attached to abandoned pipe such as a metal water pipe that used to run underground to a remote well but which, now that it's abandoned in the building, may have been also cut off outside of the building, or may have rusted away
SYSTEM GROUNDING - A Summary of Inspecting Residential Electrical System Grounding for Defects
Electrical grounding improves building electrical safety because it provides better path for current than a person, blows fuse/breaker, dissipates static, may dissipate lightning
Example of a potential shock waiting for someone: loose black wire in a metal junction box touches the side of the box. If the electrical box is connected to ground lots of current will flow (this is a short circuit) and the fuse or circuit breaker protecting the electrical circuit will blow or trip.
But if the electrical box is not grounded, current flows through a person when the electrical box or anything connected to it (electrically) is touched, if the person has the bad luck to also be herself grounded (say by touching building piping or standing on a wet floor).
Questions & Answers regarding this article
Questions & answers about how to inspect residiential electrical wiring ground system, & about defects in electrical ground system wiring.
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Timothy Hemm, Yucala, CA, contributed the photographs of electrical equipment installed in California buildings. Mr. Hemm can be contacted at TimHemm@yahoo.com
Special thanks to Bud - a master electrician in Minnesota who contributed text and suggestions for explaining why we need electrical grounding, and for discussing the shortcomings of neon testers and plug-in receptacle testers - 1/22/2009
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)
Aluminum Wiring Information Website Aluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
Electrical Panels, How to Inspect in buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
Federal Pacific Electric (FPE) Stab-Lok Circuit Breaker Panel Hazards Website - Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
"Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
"Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
"Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
"Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
"Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
"Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
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