Electrical ground inspection
How to Inspect Residential Electrical System Grounds, Ground Wiring, Grounding Conductors, Grounding Electrodes
ELECTRICAL GROUND SYSTEM INSPECTION - CONTENTS: Class on how to inspect electrical panels, home inspection procedures and safety, definition of ground, grounding, grounded, grounding conductor, grounded conductor, bonding, earth, earthing
POST a QUESTION or READ FAQs about how to inspect residential electrical wiring ground system, & about defects in electrical ground system wiring
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Electrical ground system inspection procedures & checklists.
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.
Guide to Inspecting Electrical Service Grounding Equipment for Defects
\Here we define electrical ground, grounding, bonding, and earthing terms and explain why there are important differences among these words.
[Click to enlarge any image]
“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.”
Watch out: improper electrical grounding at a building can cause or contribute to fire, electrical shock, even death. If you are not qualified / trained in working safely with electrical wiring, leave any suspect electrical circuits off and ask for help from a licensed electrician.
Also see DEFINITIONS of ELECTRICAL GROUND, Grounding Electrode, Grounding Conductor, Grounded Conductor, Ground Wire, Neutral Wire, Ground Rod, for definitions of these confusing electrical terms.
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.
Aluminum - bare vs. insulated (risk of corrosion, break in wire, loss of safe grounding - illustrated below)
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
to the metal casing of a private well
Why is Building Water Supply Piping Connected to the Ground System?
The NEC (section 250-81 through 250-83) requires that the electrical system connected
to all of the following, if available for grounding purposes:
metal frame of building [if the building has metal framing]
metallic water pipe with 10 lineal feet in contact with earth
The reason we ground in-building plumbing is not to provide an additional grounding conductor in a building but to ground the plumbing.
Picture someone knocking a toaster into a stainless steel sink or into any sink with a metal drain and drain piping.
If the sink and piping are grounded the fuse or breaker will blow. If not, the system is waiting to electrocute the building occupant when s/he touches the live water/toaster in the sink and perhaps a nearby metal faucet, radiator, or other component that is ultimately connected to earth.
Similar hazards exist at other building locations such as basement laundry equipment & sinks, at building tubs and showers, etc.
In a properly-wired building, the grounding conductor and bonding system do not normally carry current, and would not be blamed for copper pipe pinholing etc. The grounding system is intended to conduct electrical current only in the event of a fault or emergency [such as a lightning strike or a hair dryer dropped into the bath tub or sink].
This article series describes procedures for safe and effective visual inspection of residential electrical systems including electrical panels and other components, when the inspection is conducted by trained building
inspection professionals, home inspectors, electrical inspectors, and electricians.
This information was presented by
Daniel Friedman - InspectApedia.com, at & discussed by the Hudson Valley chapter of the American Society of Home Inspectors -
HVASHI Seminar 12 Sept 2002, Updated April 2006, April 2009.
Carson Dunlop's sketch at page top shows where the electrical inspection starts at a residential property.
Table of Electrical Ground Wire Sizes Required by Electrical Service Size
Ground Gauge CU (Copper)
Electrical Service Grounding Defects & Conditions to Check For During an Electrical Inspection
Here are the Most-Common Electrical Service Grounding Defects & Conditions
not found in sub panel feeder (a)
attached to plastic pipe (b)
attached to abandoned pipe
loose or missing connections
(a) or (b)
no water meter bypass or other dielectric plumbing fitting bypass (bonding jumper)
local grounding electrode conductor not found in main panel
ground bond between neutral and ground and panel enclosure not found in the main panel
no water meter/water shutoff valve bypass (bonding jumper) (a)
neutral (the grounded conductor) bonded to ground downstream of box (or upstream)
neutral bus not bonded to the ground bus (equipment grounding conductors & ground bus) at main panel
main panel not bonded to grounding electrode conductor and ground bus
undersized grounding electrode conductor wire
ground rod (grounding electrodes) cut off or short (or only one grounding electrode connection at new construction)(b)
What Other 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 DIELECTRIC FITTING CODES or non-conductive sections of piping (such as plastic piping) then the building plumbing system may not be safely grounded.
Spelling note that may help some web searches: it's not dialectic pipe fittings, but dielectric pipe fittings.
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.
The Dialectic Philosophy of Dielectric Electrical Separation of Materials
Thanks to reader Bill O'Reilly (not that one) for the following excellent comment.
7/21/2014 Bill O'Reilly (not that one) said:
There's a spoonerism in the "Electrical ground inspection" article in the phrase ..."if the building plumbing includes dialectic fittings"... Dialectic fittings could be decorative, but wouldn't serve the intended function.
The word dialectic should be dielectric.
A dialectic is a form of formal argument first popular in the golden age of greece. [Dialectic is defined as The art of investigating or discussing the truth of opinions, inquiry into metaphysical contradictions and their solutions - Ed.]
A dielectric separates two electrically conducting materials so that they can be at two different potentials, more formally an electric di-pole. In the formal sense, a dielectric can be a solid (e.g. glass, porcelain, nylon, polyvinylchloride), a liquid (e.g. oil), a gas (e.g. dry air, sulfur hexafluoride), or a vacuum, which is nothing at all. In the particular sense of the phrase's context, the dielectric blocks the flow of electrons between the dissimilar metals, thus preventing the flow of dissolved ions from the water to the cathode and (metallic) ions from the anode into the water.
Suggested citation for this web page
XXX at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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.
More about the galvanic scale and corrosion between dissimilar metals is at
List of Still More 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 DOUBLE FAULT, LOSS OF ELECTRICITY, 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).
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, February 2013, March 2014, July 2014, December 2014
I am replacing my service panel,in my condo, and the conduit running from the sub panel is being used as the earth ground. How can I test this ground?
When the conduit is being used as the earth ground it must meet certain UFER specifications and impedence requirements. Below is a general answer discussing local electrical ground electrode testing.
See ELECTRICAL GROUND REQUIREMENTS
If a local ground is isolated from the electrical company's ground (neutral wire in the panel) and does not conduct electricity or shows high resistance (or more generally, high impedence) it is not safe. How much is "high impedence" when testing an electrical ground system at a building?
The NEC specifies 25 ohms as an acceptable limit
for electrode impedance. The IEEE Standard 142
Recommended Practice for Grounding of Industrial
and Commercial Power Systems (“Green Book”)
suggests a resistance between the main grounding
electrode and earth of 1 to 5 ohms for large
commercial or industrial systems. - Fluke Corporation, "Checking ground electrode impedence for commecial, industrial, and residential buildings", [PDF] Fluke COrporatio, PO BOx 9090, Evrett WA, USA 98206, Tel U.S.A. (800) 443-5853, Fluke Europe, B.V., PO Box 1186, 5602 BD
Eindhoven, The Netherlands,
In Europe/M-East/Africa +31 (0) 40 2675 200 ,
In Canada (800)-36-FLUKE
From other countries +1 (425) 446-5500
Watch out: this test needs to be performed by a trained electrician as there are shock and electrocution hazard risks. As Fluke and other experts point out, to perform testing of the local grounding electrode it must be disconnected from the building. The ground testing instructions that we cite below include additional important safety warnings and procedureal details from which we excerpt. From reading the literature our opinion is that this test is technically difficult, requires expertise, and should not be attempted by a homeowner nor by anyone else who lacks the necessary expertise.
Here is an excerpt from Fluke Corporation, a producer of a wide range of electrical test equipment:
There are two types of ground impedance testers.
Three and four point ground testers and clamp-on
ground testers. Both types apply a voltage on the
electrode and measure the resulting current.
A three or four-pole ground tester combines
a current source and voltage measurement in a
“lunch box” or multimeter-style package. They use
multiple stakes and/or clamps.
Ground testers have the follwing characteristics:
AC test current. Earth does not conduct dc
Test frequency that is close to, but distinguishable
from the power frequency and its harmonics.
This prevents stray currents from interferring
with ground impedance measurements.
Separate source and measure leads to compensate
for the long leads used in this measurement.
Input filtering designed to pick up its own signal
and screen out all others.
Clamp-on ground testers resemble a large clamp
meter. But they are very different because clampon
ground testers have both a source transformer
and a measurement transformer. The source
transformer imposes a voltage on the loop under
test and the measurement transformer measures
the resulting current. The clamp-on ground tester
uses advanced filtering to recognize its own signal
and screen out all others. - Op. Cit.
Grounding Electrode Testing Shortcut using the 62% Rule
Fluke Corporation describes a simplified grounding electrode test in which the technician drives additional spikes into the ground to permit several measurements fof impedence that are compared at different distances from the grounding electrode under test. Measurements are made by connecting test leads to the grounding electrode, to a "current spike" driven at a specified distance "d" from the test electrode, and one to three "potential spikes" driven at a distance equal to 62% of distance "d". Details are in the document that we cite and link-to above.
You may be able to use a shortcut if your test meets
the following criteria:
You are testing a simple electrode (not a large
grid or plate)
You can place the current stake 100 feet or more
from the electrode under test
The soil is uniform
Under these conditions you can place the current
stake 100 feet or more from the electrode under test.
Place the potential stake at 62 % of the distance
between the current stake and the electrode under
test and take a measurement.
As a check, take two
more measurements: one with the potential probe
3 feet closer to the electrode under test, and one 3
feet farther away (see Figure 5 in Fluke's document). If you are on the flat
portion of the fall-of-potential curve then the readings
should be roughly the same and you can record
the first reading as your resistance. - Op. Cit.
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 "Publication No. 37: Electrical Grounds - A Controversial Necessity", The State of Connecticut Department of Public Health
Environmental Health Section, Private Well Program
450 Capitol Avenue, MS#51REC, PO Box 340308, Hartford, CT 06134
Phone: 860-509-7296, retrieved 2/7/13, original source: http://www.ct.gov/ [copy on file]
At ALUMINUM GROUND WIRES we discuss proper repair of aluminum ground wires found in solid conductor branch circuit wiring.
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: firstname.lastname@example.org
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
"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.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"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.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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)
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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