Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
AFCIs ARC FAULT CIRCUIT INTERRUPTERS
ALUMINUM WIRING HAZARDS & REPAIRS
AMPS VOLTS DETERMINATION
AMPERAGE MEASUREMENT METHODS
APPLIANCE EFFICIENCY RATINGS
BOOKSTORE - ELECTRICAL
Cadet & Encore Heater Recall
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
Classified CIRCUIT BREAKER WARNING
CUTLER HAMMER PANEL FIRE
CORROSION in ELECTRICAL PANELS
DEFINITIONS of ELECTRICAL TERMS
DIRECTORY OF ELECTRICIANS
DMM Digital Multimeter HOW TO USE
ELECTRIC METERS & METER BASES
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRIC PANEL AMPACITY
ELECTRIC PANEL INSPECTION
ELECTRIC PANEL MOISTURE
Electric Power Frequency Table
EMF RF FIELD & FREQUENCY DEFINITIONS
ELECTRICAL GROUND SYSTEM INSPECTION
ELECTRICAL SERVICE DROP
ELECTRICAL SERVICE ENTRY WIRING
EMF RF FIELD & FREQUENCY DEFINITIONS
FIRE SAFETY Checklist, CPSC
GFCI PROTECTION,Testing GFCIs AFCIs
HEATING COST FUEL & BTU Cost Table
HEAT TAPE USAGE GUIDE
Hertz - Definitions of KHz MHz GHz THz
KNOB & TUBE WIRING
LIGHTING, EXTERIOR GUIDE
LIGHTING, INTERIOR GUIDE
LIGHTNING PROTECTION SYSTEMS
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
MURRAY SIEMENS Recall
PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS
REMOTE ELECTRIC POWER, PHOTOVOLTAIC
RUST in ELECTRICAL PANELS
SAFETY for ELECTRICAL INSPECTORS
SE CABLE SIZES vs AMPS
SIEMENS MURRAY Recall
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
UNDERGROUND SERVICE LATERALS
VOLTS / AMPS MEASUREMENT EQUIP
VOLTAGE MEASUREMENT METHODS
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved.
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.
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.”
See Definitions of Electrical Ground, Grounding Electrode, Grounding Conductor, Grounded Conductor, Ground Wire, Neutral Wire, Ground Rod, for definitions of these confusing electrical terms. Readers of this article should also be sure to review False Ground at Receptacles where we describe false grounds and un-grounded or un-polarized electrical receptacles and circuits, and see Safety Hazards and Safe Electrical Inspection Procedures for Inspectors examining Residential Electrical Systems and Local Electrical Grounding for safety procedures during inspection of the grounding system. Sketch courtesy of Carson Dunlop Associates.
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.
Sketch courtesy of Carson Dunlop Associates.
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:
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.
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.
As Carson Dunlop's sketch shows here, from the main electrical panel a grounding conductor connects to:
The NEC (section 250-81 through 250-83) requires that the electrical system connected to all of the following, if available for grounding purposes:
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].
Details about the causes of copper pipe pinhole leak complaints are at COPPER PIPE PINHOLE LEAKS, Pinhole Leaks: cause, cure, prevention
NEC Citations on grounding water piping
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.
See Definitions of Electrical Ground, Grounding Electrode, Grounding Conductor, Grounded Conductor, Ground Wire, Neutral Wire, Ground Rod, for definitions of these confusing electrical terms.
At ALUMINUM GROUND WIRES we discuss proper repair of aluminum ground wires found in solid conductor branch circuit wiring.
Readers should see our complete electrical ground inspection information at ELECTRICAL GROUND SYSTEM INSPECTION
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.
Readers of this article should also be sure to review Safety Hazards and Safe Electrical Inspection Procedures for Inspectors examining Residential Electrical Systems and should pay special attention to the following chapters from that article: ELECTRICAL PANEL INSPECTION SAFETY - Removing Electric Panel Covers - Electrical Panel Cover Screws - Electrical Panel Interior Hazards - Testing Main Breakers or Fuses and Inspect Breakers, Fuses.
Carson Dunlop's sketch at page top shows where the electrical inspection starts at a residential property.
(a) Equipment grounding conductor defect
(b) Grounding electrode conductor defect
More about the galvanic scale and corrosion between dissimilar metals is at GALVANIC SCALE & METAL CORROSION.
What Other Defects Should We Check for in an Electrical Grounding System?
Green link shows where you are in this article series.
More about the galvanic scale and corrosion between dissimilar metals is at
At ALUMINUM GROUND WIRES we discuss proper repair of aluminum ground wires found in solid conductor branch circuit wiring.
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.
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).
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!
Readers should 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.
Frequently Asked Questions (FAQs) About How to Inspect the Electrical Ground System at Buildings
Question: testing for or controlling voltage leakage
How I can control voltage leakage ? - Rikio 8/9/11
Reply: find and fix the wiring error
Rikio I'm not sure I correctly understand the question but in general, if you are measuring voltage leaking say to ground, you want to find and fix the wiring error.
Question: can I put plants near the grounding electrode
can i put a shrubs or plants near the grounding system, or can i put river rocks surrounding the ground system? - David 8/10/11
Question: pinhole in copper water pipe under the slab
I have a home that is 7 yrs old in Burleson Tx. We are on a co-op water supply. I recently had a pin hole in my copper water pipe under the slap. I though it was the water but had the water dept lab test my water and all was normal. I then read about electrolysis could cause this. I do have a ground on my water pipe and a rod out side my main. I checked whit a meter and I do have continuity between the main panel and my plumbing and my gas pipe to the hot water. can this possible cause my plumbing to fail?
The water has been ruled out so it has to be something else the pin hole was from the inside out and my house water connections are green and blue. need some help bad. I did disconnect the one ground off the plumbing when I read about the electroylis. Please advise.
Reply: Causes of pinholing in copper water supply or drain piping
If you do nothing but fix the pipe and the problem never recurs I'd suspect the pipe itself. But if it were me, I'd also have a licensed electrician check that the home's grounding and neutral systems are properly wired, that the grounding electrodes are properly sized and installed, and that there are no stray currents on the neutral system nor shorts or leaks in the wiring system (an AFCI or GFCI can help detect these too).
Question: comment that copper in concrete corrodes
Copper pipe failure in concrete is common. - anonymous 12/1/11
Yes, Anon, depending on the chemistry of the concrete and also moisture exposure there can be problems with corrosion - which is why for grounding conductor wiring the electricians I know use insulated grounding conductors. I haven't seen that demanded for copper piping.
Question: is a lead water line from the street a good electrical ground?
My main water line coming in from the street is lead. Can I ground the electrical panel to the lead pipe? I read that lead does not conduct electricity very well. Thanks. - Brad 6/2/12
Indeed it's common to see the electrical panel bonded to a lead water main entering the building.
Watch out: Lead conducts electricity but corrosion and unreliable connections within the piping make it an unreliable main electrical ground.
Good procedure would be to connect a ground to the lead water main but ALSO to install two (current NEC) driven ground rods at the property. I would not install less than one additional grounding electrode (ground rod). For a reliable and compliant installation, use two.
Question: follow-up on pinhole leaks in copper piping traced to bad (grounded) neutral connections at the utility transformer
Dan, concerning the pin hole pipe leak and all the green and blue plumbing from Oct. 19 & 21, 2011. I have seen this before and traced it to bad grounded (neutral) connections at the utility transformers or tap boxes causing all the neutral loads to be carried on the grounding system such as the copper plumbing.
I even seen it in one house but show the signs of trouble in a neighbors house because of a common city water pipe. This situation eats the copper water piping from the inside out and can cause green/blue water color, usually the first sign.
Also, these pin hole can develop because of excessive flux being used before sweating. The excess flux lays in the bottom of the pipe and corrodes the copper, hence pin holes on the bottom only. - Rod, electrical contractor, 8/1/12
Question: jumper across dielectric fittings is asking for galvanic corrosion
You show a jumper wire across a dielectric plumbing connection (between copper & galvanized pipe). This will promote galvanic corrosion & make the dielectric connection pointless. Instead of at the connection the corrosion will now take place inside the galvanized pipe near the jumper wire clamp.
Grounding the plumbing does not make a house safer. It places half an electrical circuit through out the house. This increases the likelihood of connecting that circuit with some current. - Galvanic 9/20/12
If we don't jump across a non-conductive dielectric fitting on water piping then the water piping is not grounded. By current NEC, metal piping may not be used as a grounding conductor, but metal water piping in contact with the earth for a length of ten feet or more, that piping is indeed connected to the electrical ground system.
For protection from lightning and possibly leakage from a high voltage transformer, the current National Electrical Code (NEC) requires two grounding electrodes at a building. If one of these is water piping it is tested and must show less than 25 ohms of resistance to earth.
Current NEC Citations on grounding water piping
Typically, pinholing in copper piping that is traced to an electrical grounding problem (electrolysis) is, if we exclude neutral/ground wiring errors, traced to inadequate local grounding electrodes.
Thanks for the interesting comment. I'm not sure where your surmise takes us, since there are both code and basic safety reasons for grounding house plumbing. Also I am nor sure which jumper you saw, but connecting a ground between similar metals ought not create the concern youncite. Can you give us a citation or article to review?
We ground building water piping for electrical safety for the occupants, not to provide an additional electrical ground path
The reason people 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.
Incidentally, as we discuss pinholing and bad neutral connections, keep in mind that the return path for current in a building's electrical system is not intended to be primarily through the building's local grounding electrodes. Rather it is on the neutral wire that is connected back to the pole transformer. See LOST NEUTRAL Shocks Homeowner for details of what can happen when this connection is not made or goes bad.
in a house with no ground electrical ie two prong outlets not three, will a circuit tester read correctly? - Jim 10/31/12
Questions & answers or comments about how to inspect residiential electrical wiring ground system, & about defects in electrical ground system wiring.
Ask a Question or Enter Search Terms in the InspectApedia search box just below.
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.