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MOISTURE SOURCES in PANELS
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PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS
REMOTE ELECTRIC POWER, PHOTOVOLTAIC
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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 2014 InspectApedia.com, All Rights Reserved.
\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.”
Sketches above and at page top 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.
More details about electrical grounding can be read at ELECTRIC SERVICE GROUNDING SYSTEM INSPECTION and
and at OLD HOUSE ELECTRICAL WIRING.
Also, see details about electrical grounding at ELECTRICAL CIRCUITS, SHORTS,
and at ELECTRICITY BASICS, HOW IT WORKS.
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.
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?
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:
More about the galvanic scale and corrosion between dissimilar metals is at
Electrical Code Requirements for Grounding Water Pipes: NEC Citations on grounding water piping
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).
As a result, the ground path was electrically live when it should not have been, leading to an electric shock.
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.
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
Watch out: for safety, also review SAFETY HAZARDS & SAFE ELECTRICAL INSPECTION PROCEDURES for Inspectors examining Residential Electrical Systems
Continue reading at ALUMINUM GROUND WIRES or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
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
(Nov 5, 2012) HARDIK SANJAYKUMAR SHUKLA said:
Can u pls suggest a device to check if a motor is silently attached to a pipe.
A continuity tester
(Feb 17, 2013) CathyA said:
Since this fall, after a smart meter was installed on our home, we have had a ringing noise in our electrical wiring, dimmer switches, water pipes. An electrostatic filter, two clock radios and a wireless router are no longer working. There are also sparks jumping out of some outlets when we plug in our laptops (we now use surge protectors). The utility says the meter is fine. There is a transformer on a phone pole at the foot of our driveway which they also checked. The gas meter was checked (sort of). I am wondering if this is an easy (not too expensive) or difficult (expensive) problem to fix and am assuming I need an electrician. For instance, is it in the $100's or $1000's of dollars? Just an educated guess would help. Thanks.
(Mar 9, 2013) Charles said:
The grounding wire from my circuit box is attached via a clamp to a hot water copper pipe. Just a few inches further, and it could be attached to a cold water copper pipe. My question is, would it be better if the grounding was done to the cold water pipe, since then it would not have to go through the water heater, and be more directly connected to the city main water supply line?
It can be confusing figuring out if your water piping is actually serving as an electrical ground (it would have to be continuous metal, into soil outdoors, for a suitable distance and depth) or if instead the connection you see is intended as a safety feature to ground the building piping.
Certainly we wouldn't expect a workable ground connection for the electrical system to run through piping and the water heater.
As you will read in this article series, current codes want two grounds at the home - via grounding electrodes, for safety reasons.
Thanks for your response Dan.
I did not open the circuit box, but inspecting all the wires coming out of it, this one seemed to be the only one consisting of a few exposed copper wires twisted around each other. If this was meant to ground the house piping, should it be connected to the circuit box? If there is another wire going to electrodes, where else should I look to find it? Even if this was meant to ground the piping, would it be better if it was connected to a cold water pipe?
This all started when I went to insulate some of the hot water pipes in my basement. That's when I ran across the wire attached via a clamp to the hot water pipe. I was not rewiring or looking to update the grounding for my electrical system. It is a 1915 house which looks like it had its wiring updated, maybe in the 90's. Other than what may be in the hot water heater, there is no other non-metallic materials in between it and the water meter, and then its metallic piping going out of the house from there. In any event, is it OK, if not better, to attach this wire to the cold water pipe.
PS: While I was down there I found another wire going from the phone line also to another hot water pipe for grounding. Did they just not care back in the day what pipe they were grounding to, or was it actually better to use the hot water pipe than the cold one?
Sounds odd Charles. Send me some sharp photos so i can see the ground wires coming out of the panel and where they go. You may need an electrician to be sure your house groundis proper and safe.
Question: how often should the electrical earthing system be inspected in erratic power areas?
(Feb 10, 2014) Folarin said:
In developing countries where power supply is erratic, what frequency would you advise inspection of electrical and earthing systems?
Interesting question Folarin, I don't know a solid answer.
It seems to me that in thinking about electrical ground safety I'd be less worried about erratic power delivery or varying voltage levels in delivery and more worried about conditions that immediately affect the safety of the electrical system, or if we confine that safety to a subtopic of grounding, and if I were thinking off the cuff about country differences I'd want to identify
- areas where grounding is not adequately provided
Question: got shocked touching the mobile home door
(Feb 16, 2014) Anonymous said:
My trailer is grounded but it still shocks you when you open the door can't find the problem
Watch out: Anon, you really should call a licensed electrician - a ground fault such as the one you describe could kill someone. Certainly I can't imagine diagnosing the problem by message exchange - you need an experienced eye on the scene.
Question: finding voltage on the ground wire - is that OK?
(Mar 6, 2014) steve said:
i'm measuring +/- 15 volts on a ground wire at light fixture. Is this normal?
it is not normal to find voltage on the ground wire; that wire carries current in the event of a fault or short.
(Mar 12, 2014) Scott said:
I want to erect a 40 meter ham radio antenna onto our old outdoor tv antenna mast. The more I read about what it takes to ground all three legs of the mast correctly for lightning protection, and to then properly bond it to the house electrical ground, the more I am inclined to realize I need an electrician to supervise my work and an inspector to bless the whole project. My question is, when it comes to connecting the recommended #4 solid copper wire to each grounding rod, is it true that the grounding rod can only be fully buried in the ground if the wire was cad-welded, and if it were clamped on, the grounding rod top needs to remain slightly above ground so that it can be inspected annually? I'm inclined to think that the cad-welded idea is the better solution.
Scott, thanks for the interesting question. I don't have an answer but will do some research - as you might too, using Google Scholar or NEMA or the NEC.
Start at NEC Article 250 — Sections 250.20 through 250.34
www.mikeholt.com - Mike Holt's forum has the most clear and authoritative discussion of grounding I've been able to find. I've asked Mike for some help on your question.
In general, I have never, in thousands of inspections, come across a welded ground wire-to-electrode connection at a building. Most often we see a few inches of grounding electrode above ground and a clamp connecting the grounding conductor to the ground rod.
A shortcut might be to check with your local building department to see what they will accept.
I'll post further when I can find an authoritative citation on the connection we are discussing.
Mike Holt adds,
Question: bonding to a gas meter
(July 31, 2014) Anonymous said:
Question: can damage to the outdoor water meter affect the indoor meter reading?
(Aug 18, 2014) S. Moore said:
If I understand the question correctly, you ask if damage to an outdoor water meter would affect the proper operation of a subsequent water meter that is down-stream from the damaged one. I don't think so.
The only oddball case that occurs to me would be one of damage to an upstream water pressure reducer/meter combination that sent a surge of unanticipated high water pressure into a building. That might cause leaks at or damage to building plumbing system components including piping, valves, or even a meter.
Question: ok to splice grounding wires?
(Sept 4, 2014) email@example.com said:
Generally grounding wires can be spliced, with some exceptions where use of a continuous conductor is recommended. An example of the latter is the wire connecting the building metal water supply piping around a water meter an onwards to the grounding electrode.
(Sept 12, 2014) Sam Herschler said:
(Sept 13, 2014) DanJoeFriedman (mod) said:
Question: test ground wire connections at an electrical switch or outlet
Can I test ground wire connections at an electrical switch or outlet?
A trained electrician (that is someone who knows how to avoid getting electrocuted while messing with wiring) might use a DMM or VOM to check for current flow from hot to ground; if the ground is disconnected no circuit would be completed and no current would flow.
I also check that the metal box is grounded and as we warn in these articles, we emphasize the importance of following NEC on grounding and grounded conductor wiring and connections - e.g. don't rely on a "ground" obtained through the receptacle or switch mounting strap.
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