A contractor informed us that our main electrical panel is not actually
connected to ground. He proposes to install a copper tube to earth below
the panel and then connect that to the ground wire input on the panel.
My questions are:
1) If the panel is actually connected to some other ground in the building,
is there any harm in connecting to a real-earth ground in addition?
2) Once the ground wire is attached, what would be a safe way to test the
installation to make sure that a randomly selected circuit fed by that panel
has its ground wire attached to the real-earth ground?
Did he check the meter can? Was this ever inspected?
There is no problem with multiple ground electrodes anyway. The more
There is no way for a homeowner to really test the ground electrode
system but the code says if you are not sure, drive 2 rods.
The circuit tester will check the ground paths inside the house to be
sure each outlet is connected to the ground bus.
1. No, there is no harm. Originally panels were bonded to cold water pipes
for a ground. Then later a ground rod (5/8"x8') was driven in as a
supplemental (backup) ground.
2. You can't test it without the correct equipment. But then again, it's not
up to you to test it, that's why you call an electrician who is trained to
do this. If you're questioning the word of the contractor that was there,
then A don't use him, or B call someone else for a second opinion.
Unless your electrical contractor is planning to install a second
ground rod in addition to the first he/she has to conduct a ground
impedance test using rather expensive equipment. The test result has
to show that the impedance to earth of the first rod is twenty five
ohms or less. If the tested impedance is greater than twenty five
ohms then a second electrode is required. If he/she is going the two
electrode route instead of testing you should ask them to sink the
second rod at least twice the length of the rods being used apart.
The code does allow a separation of only six feet but that is to allow
for urban installations were a greater separation cannot be achieved.
Best practice is to separate driven rods by twice their length and to
separate them from underground structures such as foundation walls by
at least their own length. With eight foot rods that means eight feet
out from the foundation wall were possible and then another sixteen
feet to the second rod were feasible. That provides separate and
complete shells of earth for each rod to dissipate any fault current
resulting from a lightning strike to the lines or a high voltage power
cross caused by line damage. The more of that fault energy that is
successfully dissipated the less of it will enter your home on the
What types of electricians would be likely to have proper ground testing
equipment? I'm thinking someone who installs high voltage panels or
generally works with high voltage equipment is likely to be well versed in
grounding, but how to find such a specialist?
The last time I looked that NEC was rather tolerant of what most would
consider to be a "bad" ground.
I believe the old rules said that the "ground resistance" of THE ground
rodshould be 25 ohms or less and if it didn't meet that requirement a second
ground would have to be installed.
Rather than screw around, most electricians simply installed a second ground
The "real world" solution to your problem is to install 2 ground rods (8'
long, etc) and connect them to the panel ground.
There are some arcane rules about how connections between the grounding
wires should be made (yeah, wire nuts aren't gud enuf.)
It's useful to speculate on what is the most "dangerous" condition.
Most would say that it would be a broken neutral between the power company
transformer and you entrance. If your loads are unbalanced, you can end up
with your neutral being 120 volts from ground and each and every "ground"
pin on each outlet 120 volts from ground.
In such a situation, the main thing your "ground rod" does is reduce the
voltage gradient between "real" ground and "local" ground.
That, alone, is sufficient justification to install your two ground rods and
bond them to the panel and local neutral.
In these situations, the "more the merrier" rule applies. It certainly
wouldn't hurt to run a copper cable around the house and connect several
ground rods to that cable and, of course, bond that cable to your two rod
"official" ground which, BTW, is also used (or should be used) by the cable
company, the telephone company, and dish/tv antenna installers.
The better your "local ground" is the lower the potential difference between
"power company ground" and your "local ground" can be.
It went largely unnoticed by a lot of people but the NEC now says "if
available" steel in the footer shall be incorporated into the
grounding electrode system. A lot of building departments are saying
you will make it available and you will install the Ufer ground in any
construction that gets a footer. It is part of the footer inspection
now most places..
That is - the building system "ground" is 120V from earth.
I am not fond of the multiple meanings and functions of "ground" and
"ground wire". It contributes to the difficulty reading the NEC chapter
You weren't looking at fault current, but adding fault current to the
Suppose you take a simple example of a parking lot light with only a
ground rod (no ground wires) and a near miraculous resistance to earth
of 10 ohms. There is a short from hot (120V, 20A circuit) to the metal
pole. No worry - we have a ground rod. The current to earth is 120V/10
ohms = 12A. If the breaker has the allowed continuous load of 16A, that
gives a 28A fault current. Looking at the time-trip curves for a SquareD
breaker, it will trip in 30-200 seconds. If the circuit is loaded
lighter the breaker may trip - never.
But the rod drags up the local earth potential? As a rule of thumb, 70%
of the voltage drop in the earth away from the rod is in the first 3
feet. From the earth over 3 ft from the rod to the pole the voltage will
be 85V or more. (This is also affected by the resistance to earth at the
Now extend that to a building.
For fault current you might get better results from a metal underground
water system - but you are working with the resistance to earthing at
the utility transformer too. With a typical municipal metal water supply
the path is likely through the water pipe, to an adjacent building,
through the neutral-ground bond at that building, thorough the neutral
service wire for that building, back to the supply transformer.
The NEC requires an effective path for return of fault current. "The
earth shall not be considered as an effective fault-current path."
I thought "concrete encased electrode" was a recent addition to the
code. I was surprised that it appears as far back as I looked, 1984,
with language "if available on the premises..." IMHO it is not
"available" unless a connection is brought out - would be interesting
what a court would say....
But the language starting 2005 is electrodes "that are present at each
building" In most buildings 20 ft of rebar, which may be tie-wired
together, is "present". And it is perhaps clearer in the exception that
the code wants the electrode for new construction.
I don't remember when they started requiring a Ufer ground here - I
think it was with the new language of 2005. It wasn't flagged in the
code change book I read. But Ufer replaces ground rods - a major plus.
Am I reading right that your inspection is by the footer inspector, not
an electrical inspector?
Yes that is true in 1&2 family. The Ufer will be verified by the
structural inspection when they look at the footer. (although the
electrical inspector and the structural inspector are usually the same
guy these days) Typically it is just a piece of rebar that is turned
up into the wall and the 4ga copper connection is made to that later.
If somebody screws up and grouts the cell with the Ufer in it, they
will be chipping out concrete to make it available again. Hence the
In commercial they may have a separate electrical inspection for the
Ufer. I know I have driven 150 miles to look at an acorn clamp and 10'
of copper wire. I finally started telling them to take a picture and
Email it to me if it was 2 counties away..
I agreed with most of the ideas replied back to you, I do see a few options,
-Checking with your city representatives in the electrical department and
they will guide you in the proper direction with permits.
-You can also look at popular electrical installers, perhaps people with a
long history of work through home electrical wiring, perhaps they can send
someone out to give you an overview of what needs to be done, then they will
guide you in the direction of proper permits which need to be obtained.
-You can do alot of reading and research and know your stuff, so when you
call someone to do the work you will have an idea of what needs to be done.
(not the most popular if you don't like to do alot of research).
-Assume that your electrician knows what he is doing is correct and
kick-back and relax. (not recommended).
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