
The 5 foot ground rod and its use in the National Electric Code (2018) - turtlegrids
https://iaeimagazine.org/magazine/2018/07/30/the-5-ft-ground-rod-and-its-little-known-use-in-the-nec/
======
FiatLuxDave
Once I had a situation where the length of the ground rod mattered.

We were building a fusion reactor prototype, and as far as I am aware the NEC
code doesn't really have a section for that. I'm sure that much of what we did
was probably against best practices.

We had a number of high voltage power supplies running in one room of our lab,
and on days when the humidity in the air was low, the ionization in the air
would charge up all the metal surfaces in the room. So, even if something was
not connected to a high voltage, you would get a nasty shock when you touched
it. All these devices were connected to the normal, "third prong" wall socket
ground, but apparently the route through the building to ground was too
resistive to handle the large amount of ionization in the air.

When working in a room with 180,000 volt power supplies, random shocks rapidly
become more than annoying.

Spence, our electrical engineer, had the idea that the quickest way to fix the
problem was to run a grounding rod into the soil right outside the window. We
pounded a rod into the ground with a sledgehammer as far as we could, which
was about 5 feet, I guess. Then we ran a 1/4" copper cable from the rod,
through the window to connect to the main reactor chamber.

This worked great! At least for a couple of months. Our lab was located in a
swamp, and the soil was basically a few meters of dried leaves. You could
actually feel the soil move up and down when you walked on it. When August
came around, it had not rained for quite a while, and the water level in the
soil had dropped below the level of the grounding rod. The dried leaves in the
soil insulated it quite well. We started getting shocks again, and it took us
many hours of troubleshooting before we realized that the ground was not
actually ground anymore.

We went out and pounded the rod a few feet deeper, which was easier now that
the soil was dry. This reached the water table, and fixed the problem.

~~~
Scoundreller
Also helps if you dump a large quantity of salty water. The salt eventually
leaves too, but helps retain some of the water and makes it more conductive.

~~~
EricE
Exactly. We had the first generation color copiers in the California high
desert and whenever paper jams became frequent we knew it was time to pour
salt water on the building grounding rod!

------
Roark66
I was building a workshop last year and as I have few old 3-phase metalworking
machines and the power comes through a 50m (150ft) buried cable I had to
install proper ground for the building and another two independent ground
connections for the lightning protection. I have no bedrock, but my soil is
pretty much 100% clay plus a football sized stones here and there around the
building. The code around here is that the ground connection should be no more
than 4 ohms resistance. I was lucky with two lightning protection grounds. For
one a single 2.4m rod was enough and for the other two rods (I had the type
that screws into each other so you can make the rod longer and longer if
necessary) were required.

However, I wanted to locate the electrical ground few meters away to avoid the
possibility of a lightning strike raising my ground potential. I ended up
having to install 6 rods to get down to 4 ohms. The first two rods were 7
ohms, the next two 2 meters away were 15 and the final two were 25 if I
remember correctly.

The take away from that story is: always measure your ground resistance. Never
assume 8ft is enough if you have a certain type of soil.

~~~
kube-system
How exactly is that measured? If you’re trying to measure the resistance
between the ground rod and actual ground, how do you get the second reference
point?

~~~
Roark66
There are two standard ways to measure. The meters that do the measurement
usually support both. First method involves two mobile shallow ground
electrodes you place 20m away from your ground rod (so electrodes are 40m
apart and your ground rod in the middle). I'm not sure how exactly it is
possible to measure this when the quality of ground those two extra electrodes
is unknown, but it works. The meters cost few thousands $ so I assume it is
not trivial.

The second method involves an already known good ground - like for example one
supplied by the electricity company. Here they usually bury galvanised steel
thick tape along their ground cables. That tape is hundreds of meters long and
underground so it is assumed to be a really good ground. It is only used to
ground outside metal bits of the power delivery equipment that are likely to
be touched by people and it is separate from the ground connection supplied in
the cable itself although one is supposed to connect it to the delivered
ground when connecting the house cable to the electricity delivery point. Then
every house is supposed to have at least two lightning protection grounds and
an extra "electricity supply" ground that is again connected with the ground
in the supply cable. Please bear in mind I'm no electrician and all of the
above is based on me observing electricians at work when they were connecting
my house, my workshop and working on lightning protection for both. I may be
mistaken on some details.

------
robomartin
L.A. County made us drive FOUR 8 foot ground rods into the ground, no less
than 8 feet apart, for our ground-mounted 13 kW solar array.

This is ridiculous beyond description and it is NOT in the N.E.C. at all.

The problem you run into with places like L.A. County is that incompetent plan
checkers just want to play "cover my ass" and make up rules. There is no
practical way to challenge them. They are the absolute authority (unless you
have millions of dollars and YEARS to fight them).

I checked with contractors and the recommendation was "just do it and don't
complain or they'll make your project a living nightmare".

So, we did.

They still made the project a nightmare to complete. They added a massive
chunk to the overall cost and it took six months longer than it should have
taken to complete it. Their interference made it such that this solar system
will likely never recover the construction costs. Well, maybe in 30 years.
It's a shame. Had I known the nightmare it is to deal with this bureaucracy I
would have invested my money elsewhere.

California is sucking more and more with time. L.A. County is even worse.

~~~
ademup
A 5/8" x 8' copper grounding rod is $14 at Home Depot; 3\4 x 10 is $33. I'm
very confused on how the extra $100 would meaningfully affect the project in
either time or BOM.

~~~
bradknowles
With respect, this is like saying “but the hard drive on Fry’s discount shelf
only costs $100, why is your NVME-over-Fiber SSD storage system so expensive?”

Hint: what the consumer can buy over the counter, and what gets used in a
professional setting, are frequently two radically different things that may
only be tangentially related.

~~~
tomku
With respect, what you're saying is absolute nonsense in the context of ground
rods. They're hunks of metal clad in copper and driven into the ground with a
sledgehammer. They're so simple that there's literally no part of a modern PC
that's analogous. The ones you can buy from Home Depot for $15 are identical
to the ones I buy from a professional electrical contracting supplier for $15
- they come off the same factory lines from the same manufacturer.

There are other components used in contracting that have a bit more product
segmentation, but the whole "frequently radically different things that may
only be tangentially related" bit is wildly exaggerated. We use the
appropriate components for the job, and often that means the same stuff you
could buy at Home Depot. You're paying for that knowledge of what's
appropriate/necessary and the labor to do the work, not for super-special
premium contractor ground rods.

------
lutorm
What do you do for grounding if your house sits on bedrock?

We _barely_ had enough for the "buried in trench, 30" deep" option at our
house before hitting the solid lava everything here is built on. (And it's
buried in mostly gravel, there is practically no dirt.)

~~~
angry_octet
A ground driven into rock or buried in dry gravel isn't going to be of much
use. Typically electrodes are buried in a mixture of bentonite and gypsum,
which is pH neutral and provides low resistance. There are also chemical
(salt) earth fills which work well but require thicker copper electrodes to
deal with corrosion. Various conductor arrangements are used, but in shallow
trenches there is always the problem of the wires being cut. A radial or
cartesian mesh burial over a larger area would be typical. You can buy
electrical mesh and ground enhancement fill for this purpose. Note that you
still need it to be below the frost layer in your region -- which varies from
15cm (California) to 300cm (Canada) depending.

An earth connected via a distant cable isn't going to be effective against
lightning (transients are high frequency and hence conductivity is constrained
by the skin effect, and long wires have high inductance even if they have low
DC impedance), and additionally is poor practice as it is more lightly to be
cut without someone knowing in the future. I doubt any EE would approve it
when other methods are available.

[https://blog.nvent.com/erico/erico-what-is-soil-
resistivity-...](https://blog.nvent.com/erico/erico-what-is-soil-resistivity-
and-how-does-it-affect-grounding/)

Cf IEEE 80 & 81

~~~
arminiusreturns
Fun story, in the Marine Corps they pee on the rods to make them ground
better. (for mobile CoC's)

~~~
angry_octet
Let's hope they do that before they power up their gear. Ouch.

The mobile radar and HF guys have lots of tricks like this, but also spend
lots of time hammering spikes with a sledgehammer.

------
erobbins
Kinda like IBM, no one ever got fired for using an 8 foot rod in a situation
where a 5 foot rod was to code.

------
walrus01
I'm kind of surprised to read that entire article and not encounter the phrase
"ohm meter" anywhere in a search. Rarely does anything serious have only one
ground rod. Three legged telecom towers will have three rods, one attached to
each leg, linked together by a ring of 6 gauge copper buried outside the
perimeter of the concrete foundation.

Multiple 5 foot ground rods in the correct configuration bonded together could
offer much more conductivity to the earth than one 8 foot. The article seems
to be obsessing about the length of the rod and not the scientifically
measurable ohm resistance.

------
alextingle
Why do the US regulations specify the method and not the result? That seems
bizarre.

Here in the UK, most earth connections are provided by the power company, but
in rural areas you may be too far from the substation, so a ground rod is
permitted - as long as it provides an earth loop impedance (Z) of less than
200 Ohm.

So if you want to provide your own earth, you have to keep driving ground rods
deeper, or adding new ones until the "Zeds" are good enough.

It looks like the US regulations permit you to bang an "8 foot" rod into dry
sand, and walk away as though that's job done??

------
segfaultbuserr
As we are talking about grounding...

I think the greatest problem that troubles me personally is that the single-
point grounding required by lightning protection is _almost never_ implemented
properly in the vast majority of installations.

I realized the existence of this problem when I wanted to install a mesh
network in a school campus, so I started reading documents about lightning
protections, amateur radio publications have good resources on it, and all of
them indicate a correct installation should eventually bound all grounds,
including mains ground, telecommunication ground and lightning protection
ground at a single-point via low-impedance connections (even if they have
their own ground rods), also, all metallic objects and structures, such as gas
pipes, fire escapes, etc, should be bounded to ground as well. This is to
prevent a voltage gradient developing between different grounding points in
case of a lightning strike, and it's usually required or implied in electrical
or building code.

However, who ever obey this rule in practice? I've seen various installations
of outdoor/rooftop Wi-Fi networks, and all the lightning protection they have
is a gas discharge tube and a ground connection of unknown quality, I don't
think the installation is legal. Also, many buildings were in compliance of
the code when they were built, but even adding an extra metal frame or a
cable-TV box will invalidate the entire lightning protection, at least from a
technical or legal perspective.

I guess the reason behind the non-compliance is that the likelihood of a
lightning strike is already low, even if it does strike, it's possible that
even a non-compliant lightning protection system can work to an extent. And if
it doesn't work, most people would just accept the damage. As a result, it's a
concern for radio hobbyist only, whose antenna increases the likelihood
significantly.

But I was still shocked when I first understood the fact that most (low-rise)
buildings don't have a technically sound lightning protection system and bet
the safety of the building on luck. And its practical consequence is: if you
want to put a rooftop antenna for amateur radio, with good lightning safety
and in compliance with the code, in many cases, the answer is you can't - the
building often doesn't even have a technically sound lightning protection
system to begin with. I read many hardcore radio amateurs redo the entire
electrical wiring at their homes to the proper standards.

High-rise buildings are much better, lightning protection is serious business,
but you are not usually allowed to put a mesh network antenna on top of them.
But if you are allowed, I've heard that some people even got a chance to have
a friendly conversation with the civil engineer who's in charge of the
building's lightning protection system and work out a solution together.

~~~
airbreather
This is called equipotential bonding and a failure to implement or maintain it
leads to occasional but tragic or fatal outcomes, we had one recently locally
where a 12 year old girl was seriously brain damaged and needing life long
care because she touched an outdoor tap.

~~~
petre
That's probably why the two faucets in the UK are required to be electrically
bound with a counductor, under the wash basin or sink. If the mains is in
contact with a pipe and not the other, touching both faucets would result in
electrocution. Also an extra argument for a single combined faucet for both
cold and hot water.

~~~
gpderetta
Separate faucets for cold and hot water is one of those inexplicable British
things for an immigrant like me.

~~~
jdsnape
it was inexplicable for me as a native too - although I recently discovered
that it was specified by older regulations as they were worried about
contamination between the hot and cold-water supplies. The hot water supply
was traditionally fed from a header tank in the loft (attic) and so wasn't
safe to drink.

~~~
Gibbon1
A British coworker said he thinks it's because authorities were worried about
the water supply being intermittent. A rooftop tank solves the contamination
back flow issue via an air gap. And provides water when the mains aren't
working.

I also suspect the British would have found a old school US style water heater
to be somewhat frightening.

[https://www.youtube.com/watch?v=AVK6bkj5Ug4](https://www.youtube.com/watch?v=AVK6bkj5Ug4)

------
watersb
Grounding, Bonding, and All That

I have been reviewing the Mike Holt NEC video seminars, just listening like
background music while I build some workbenches on the weekends.

[https://www.youtube.com/playlist?list=PLRNS1x1jcKbEgNJx26RWB...](https://www.youtube.com/playlist?list=PLRNS1x1jcKbEgNJx26RWB8O4Fm1Ny-
bxK)

~~~
wmblaettler
^ THIS - Go watch at least first video "Grounding - Safety Fundamentals" This
was a very eye-opening video. I totally misunderstood grounding before
watching this.

------
vidanay
For a great intro to grounding, check out this series of articles

[https://forums.qrz.com/index.php?threads/grounding-dos-
donts...](https://forums.qrz.com/index.php?threads/grounding-dos-donts-why-
part-1.335582/)

It's written from the perspective of a ham operator, but all the principles
are the same no matter what.

------
alkonaut
Are all domestic buildings grounded this way in the US? Here (Sweden) I
believe houses that aren’t far from transformers are only grounded at the
nearest transformer (where power is transformed from 10kV 3-phase into
230/400V 3-phase+neutral for distribution to each house.

~~~
mturmon
Yes, all domestic buildings in the US have their own earth ground, and this is
and has been required by the NEC (National Electrical Code).

Often this is a thick, 8-foot long copper rod pounded into the ground not far
from the electrical panel, connected to the panel by a ~1cm diameter copper
cable. (There are other allowed methods, including using a similar copper
electrode encased in concrete or in the building foundation.)

It looks like this (which shows a galvanized-steel rod rather than the more
canonical copper, and shows a further connection to a second ground rod, which
is not required everywhere):

[http://www.wireyourownhouse.com/panel/images/grndrodexample....](http://www.wireyourownhouse.com/panel/images/grndrodexample.png)

Also, certain sub panels (e.g., in garages) will need their own separate earth
ground, made the same way.

This "grounding electrode" is in addition to a connection ("bond") to the
domestic cold-water pipe, usually done where the pipe enters the building.
(That pipe itself may be a hunk of copper buried in the ground.) The
electrical bond to the water service is not a substitute for the dedicated
grounding electrode mentioned above, it's to ensure that the plumbing does not
become electrically charged.

~~~
mattrp
All except homes built many years ago where someone felt it was satisfactory
to clamp a single wire to the water line. I’ve seen this numerous times.

Not to mention the numerous instances of 20A breakers on 14awg. It’s simply
amazing what one will find in some homes... like the person who clipped both
ends of an extension cord to feed an outlet out of a junction box rather than
spend $20 on home wiring. Or the person who literally covered a chiseled-out
trench in plaster with painters tape to conceal wire. And on and on...

~~~
bcrosby95
> where someone felt it was satisfactory to clamp a single wire to the water
> line. I’ve seen this numerous times.

Our house was built in the 70's and that is what we used to have. After we
upgraded our panel though we got not 1, but 2 grounding rods.

~~~
mturmon
According to this thread [1], it was the 1978 code that required a dedicated
grounding electrode.

That's 40 years ago, but of course many houses have not been upgraded since
then, and some localities might not have adopted the 1978 NEC until later.

[1] [https://forums.mikeholt.com/forum/active-
forums/nec/86062-co...](https://forums.mikeholt.com/forum/active-
forums/nec/86062-code-year-for-ground-rods?t=135832)

------
fyfy18
I recently installed an IKEA kitchen hood, and was surprised that the power
connector only had two pins (IEC C17/18). The hood has a aluminium frame
(albeit painted) with metal pole switches. Can someone explain why this
doesn't need to be grounded?

~~~
lurquer
Perhaps the same reason toasters aren't. It is very likely that one will have
two hands on the toaster when one is shocked. You have two choices: ground it,
in which case the current races up one arm, through the torso, and down the
other arm (frying your heart in the process). Or, keep it ungrounded and let
the current race down your leg to the floor (sparing your torso and hopefully
taking advantage of the fact that your shoes will provide a little more
insulation that your two bare hands on metal in the first scenario.)

------
myspy
We're currently building a house in Germany and the grounding consists of a
couple dozen meters of thick (maybe 10mm) wiring which is laid out in the
concrete ground plate of the house.

~~~
petre
A couple of dozen meters? Wiring? Encased in concrete? Five to ten meters of
zinc coated 30x5mm flat bar steel bound to three to six 3/4" rods is usually
enough depending on the soil characteristics. And it's usuall buried directly
in the soil next to or around the bulding. I wonder what bulding codes you've
got there.

~~~
brazzy
The relevant code is DIN 18014. And it distinguishes between different kinds
of ground plate. Some are considered sufficiently "earth-feeling" to be
considered ground themselves, others require separate corrosion-resistant
grounding to be put in the earth around them. Zinc-coated steel is not
considered sufficiently corrosion-resistant.

Here's an article in German with some pictures of how it's done:
[https://www.elektro-
plus.com/elektroplanung/fundamenterder/a...](https://www.elektro-
plus.com/elektroplanung/fundamenterder/ausfuehrung-des-fundamenterders)

~~~
petre
Allright. This makes sense as it reduces the electro corrosion on the rebar
and also prevents other unfortunate accidents such as the hot wire coming in
contact an exposed metal part or a metal pipe which is itself in contact with
the rebar.

I have seen a scenario where ligtning struck a DHW solar panel installation,
skiped from the plumbing to the rebar and also melted hole in the plumbing
while doing so, draining all the antifreeze on the walls. In addition it
destroyed all the electronic appliances in the house. If the panels along with
the rebar would have been properly grounded, such as scenario would have been
mitigated.

------
segfaultbuserr
Note to readers: NEC is _National Electric Code_ , which is the regulation of
all electrical installations in the USA.

The NEC here is not _Numerical Electromagnetics Code_ , an electromagnetic
simulation program, commonly used for antennas, which often have a ground
connection as well. And it's obviously not the NEC Corporation, the Japanese
electric company, whose semiconductor department is now a separate company
known as Renesas.

When I first saw the title, it took me a few seconds in my mind to solve the
hash conflict here. I wonder how many people on HN know all of these entities
simultaneously.

~~~
namibj
You are not alone, at least.

