The 5 foot ground rod and its use in the National Electric Code (2018)

Once I had a situation where the length of the ground rod mattered.<p>We were building a fusion reactor prototype, and as far as I am aware the NEC code doesn&#x27;t really have a section for that. I&#x27;m sure that much of what we did was probably against best practices.<p>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, &quot;third prong&quot; 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.<p>When working in a room with 180,000 volt power supplies, random shocks rapidly become more than annoying.<p>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&#x2F;4&quot; copper cable from the rod, through the window to connect to the main reactor chamber.<p>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.<p>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.

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.<p>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.<p>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.

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.<p>This is ridiculous beyond description and it is NOT in the N.E.C. at all.<p>The problem you run into with places like L.A. County is that incompetent plan checkers just want to play &quot;cover my ass&quot; 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).<p>I checked with contractors and the recommendation was &quot;just do it and don&#x27;t complain or they&#x27;ll make your project a living nightmare&quot;.<p>So, we did.<p>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&#x27;s a shame. Had I known the nightmare it is to deal with this bureaucracy I would have invested my money elsewhere.<p>California is sucking more and more with time. L.A. County is even worse.

What do you do for grounding if your house sits on bedrock?<p>We <i>barely</i> had enough for the &quot;buried in trench, 30&quot; deep&quot; option at our house before hitting the solid lava everything here is built on. (And it&#x27;s buried in mostly gravel, there is practically no dirt.)

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.

I&#x27;m kind of surprised to read that entire article and not encounter the phrase &quot;ohm meter&quot; 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.<p>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.

Why do the US regulations specify the method and not the result? That seems bizarre.<p>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.<p>So if you want to provide your own earth, you have to keep driving ground rods deeper, or adding new ones until the &quot;Zeds&quot; are good enough.<p>It looks like the US regulations permit you to bang an &quot;8 foot&quot; rod into dry sand, and walk away as though that&#x27;s job done??

As we are talking about grounding...<p>I think the greatest problem that troubles me personally is that the single-point grounding required by lightning protection is <i>almost never</i> implemented properly in the vast majority of installations.<p>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&#x27;s usually required or implied in electrical or building code.<p>However, who ever obey this rule in practice? I&#x27;ve seen various installations of outdoor&#x2F;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&#x27;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.<p>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&#x27;s possible that even a non-compliant lightning protection system can work to an extent. And if it doesn&#x27;t work, most people would just accept the damage. As a result, it&#x27;s a concern for radio hobbyist only, whose antenna increases the likelihood significantly.<p>But I was still shocked when I first understood the fact that most (low-rise) buildings don&#x27;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&#x27;t - the building often doesn&#x27;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.<p>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&#x27;ve heard that some people even got a chance to have a friendly conversation with the civil engineer who&#x27;s in charge of the building&#x27;s lightning protection system and work out a solution together.

Grounding, Bonding, and All That<p>I have been reviewing the Mike Holt NEC video seminars, just listening like background music while I build some workbenches on the weekends.<p><a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;playlist?list=PLRNS1x1jcKbEgNJx26RWB8O4Fm1Ny-bxK" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;playlist?list=PLRNS1x1jcKbEgNJx26RWB...</a>

For a great intro to grounding, check out this series of articles<p><a href="https:&#x2F;&#x2F;forums.qrz.com&#x2F;index.php?threads&#x2F;grounding-dos-donts-why-part-1.335582&#x2F;" rel="nofollow">https:&#x2F;&#x2F;forums.qrz.com&#x2F;index.php?threads&#x2F;grounding-dos-donts...</a><p>It&#x27;s written from the perspective of a ham operator, but all the principles are the same no matter what.

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&#x2F;400V 3-phase+neutral for distribution to each house.

I recently installed an IKEA kitchen hood, and was surprised that the power connector only had two pins (IEC C17&#x2F;18). The hood has a aluminium frame (albeit painted) with metal pole switches. Can someone explain why this doesn&#x27;t need to be grounded?

We&#x27;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.

Note to readers: NEC is <i>National Electric Code</i>, which is the regulation of all electrical installations in the USA.<p>The NEC here is not <i>Numerical Electromagnetics Code</i>, an electromagnetic simulation program, commonly used for antennas, which often have a ground connection as well. And it&#x27;s obviously not the NEC Corporation, the Japanese electric company, whose semiconductor department is now a separate company known as Renesas.<p>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.