The ground is not "The Ground" and the pathology of NEC code.

[CoolWill]

Grounding started with long distance telegraph lines, and really developed with power transmission lines. When power lines began stretching miles from the "central stations", operators began noticing huge arcs sometimes jumping from generator terminals. Mechanics oiling bearings would be shocked by the unpredictable currents. It was found to be a phenomenon caused by natural charge building up in the system due to its size. It was mitigated by grounding one of the wires on the system. They began grounding at every pole and substation.

And now, because the distribution side is connected to the earth, the utilization side has to be as well, lest you find some high voltage between your water spigot and the lawn.

Grounding for short circuit protection is more properly called bonding.

 

[sunshine_eggo]

The only thing that protects from lightning is lightning protection. A direct strike on or very near a properly grounded/earthed structure will almost certainly sustain damage.

Link #6 in my signature.

 

[Starex]

The only thing that protects from lightning is lightning protection. A direct strike on or very near a properly grounded/earthed structure will almost certainly sustain damage.

Link #6 in my signature.

Without a good ground system, you’d have to purchase a hell of a lot of arrestors for every thing in your house, including yourself.
And have to replace them frequently, but it’s a good idea to use them on expensive, lightning prone equipment, like solar systems.
I highly doubt that there is a single lightning arrestor company that would recommend them as a replacement for a good grounding system.
Any lightning protection system involving lightning rods only works if it is properly grounded/ bonded to the structure s ground.

 

[Jim in Florida]

Lots of discussion on the forum about grounding your array. Most of the ground mount arrays I have seen use metal post to hold up the array. Grounding is done no matter what by those big posts. Correct bonding is a different issue.

 

[zanydroid]

Lots of discussion on the forum about grounding your array. Most of the ground mount arrays I have seen use metal post to hold up the array. Grounding is done no matter what by those big posts. Correct bonding is a different issue.

That's not guaranteed to be enough to overcome induced AC (I guess that's probably covered by the "correct bonding" part of your comment).

 

[ElectricIslander]

Confused, confounded and puzzled are terms found throughout this forum about NEC code regarding “grounding”.

We are conditioned to believe that there is object; “the ground” that is electrically quiet, safe and always zero volts and could never be a party to harming anyone or damaging our equipment.

The authors of NEC code certainly want us to believe that, but their frequent updating, changing and sometimes seemingly contradictory requirements can only lead one to wonder if is there more to the ground than they care to share.

The ground is zero volts right! But relative to what? The ground.

If you had very long meter leads and placed one on your ground rod and the other on someone’s a mile away would your meter read zero?



I am starting this discussion in hope of clearing up some of the mystery regarding grounding and possibly help people develop grounding systems that meet code and protect their equipment as best as possible.

Although this is probably not a directly useful contribution, perhaps it'll be of interest and provide a bit of a basis for the discussion that followed:

As geophysicists we image things underground in 3d based on the variation in resistivity of earth materials down there.

Electrical currents travel through the earth either from our electrical connections to it or in response to time varying magnetics fields (driven by solar flares, the solar wind etc.) or from things like lightning. Due to the 3d version of Ohms Law, variations in earth's resistivity and what we call "telluric currents" (natural electrical currents flowing through the earth) voltages of different points on the "ground" will vary.

There are enough of these natural sources of magnetic and electrical energy that if you record the variations of magnetic and electrical fields (voltage between two electrodes) at any point on earths surface for long enough, you can map the subsurface below it (this is called magneto-tellurics and is a valuable adjunct to seismic for mapping deep features within the earth).

Voltage is a measure of the energy difference of an electrical charge between two points. For household wiring the common junction between the ground rod and the bonded neutral wire is the point taken as the "zero" point. Of course, if you are measuring between two zero points any appreciable distance apart the effects of natural telluric variations in voltage and current flow will become apparent.

 

[sunshine_eggo]

Without a good ground system, you’d have to purchase a hell of a lot of arrestors for every thing in your house, including yourself.
And have to replace them frequently, but it’s a good idea to use them on expensive, lightning prone equipment, like solar systems.
I highly doubt that there is a single lightning arrestor company that would recommend them as a replacement for a good grounding system.

Not suggesting that. Just trying to dispel any idea that one is protected from lightning purely by a properly grounded system.

Any lightning protection system involving lightning rods only works if it is properly grounded/ bonded to the structure s ground.

But a proper bonded ground/earthing system for a structure does not at all guarantee that a system, it's components or the structure itself will be safe from a direct or near direct lightning strike. If you want to protect against lightning, it's a different section of the NFPA:

NFPA 780: Standard for the Installation of Lightning Protection Systems

<p>1.1 Scope.<br />1.1.1 <br />This document shall cover traditional lightning protection system installation requirements for the following:<br /><br />(1) Ordinary structures<br />(2) Miscellaneous structures and special occupancies<br />(3) Heavy-duty stacks<br />(4) Structures containing...

www.nfpa.org

 

[zanydroid]

.

 

[Starex]

Not suggesting that. Just trying to dispel any idea that one is protected from lightning purely by a properly grounded system.



But a proper bonded ground/earthing system for a structure does not at all guarantee that a system, it's components or the structure itself will be safe from a direct or near direct lightning strike. If you want to protect against lightning, it's a different section of the NFPA:

https://www.nfpa.org/codes-and-stan...t-of-codes-and-standards/detail?code=780[/URL

I’m glad you clarified that. I think we are all on the same page now.

 

[McKravitts]

Although this is probably not a directly useful contribution, perhaps it'll be of interest and provide a bit of a basis for the discussion that followed:

As geophysicists we image things underground in 3d based on the variation in resistivity of earth materials down there.

Electrical currents travel through the earth either from our electrical connections to it or in response to time varying magnetics fields (driven by solar flares, the solar wind etc.) or from things like lightning. Due to the 3d version of Ohms Law, variations in earth's resistivity and what we call "telluric currents" (natural electrical currents flowing through the earth) voltages of different points on the "ground" will vary.

There are enough of these natural sources of magnetic and electrical energy that if you record the variations of magnetic and electrical fields (voltage between two electrodes) at any point on earths surface for long enough, you can map the subsurface below it (this is called magneto-tellurics and is a valuable adjunct to seismic for mapping deep features within the earth).

Voltage is a measure of the energy difference of an electrical charge between two points. For household wiring the common junction between the ground rod and the bonded neutral wire is the point taken as the "zero" point. Of course, if you are measuring between two zero points any appreciable distance apart the effects of natural telluric variations in voltage and current flow will become apparent.

Are your images/charts available to the public?

 

[Starex]

Although this is probably not a directly useful contribution, perhaps it'll be of interest and provide a bit of a basis for the discussion that followed:

As geophysicists we image things underground in 3d based on the variation in resistivity of earth materials down there.

Electrical currents travel through the earth either from our electrical connections to it or in response to time varying magnetics fields (driven by solar flares, the solar wind etc.) or from things like lightning. Due to the 3d version of Ohms Law, variations in earth's resistivity and what we call "telluric currents" (natural electrical currents flowing through the earth) voltages of different points on the "ground" will vary.

There are enough of these natural sources of magnetic and electrical energy that if you record the variations of magnetic and electrical fields (voltage between two electrodes) at any point on earths surface for long enough, you can map the subsurface below it (this is called magneto-tellurics and is a valuable adjunct to seismic for mapping deep features within the earth).

Voltage is a measure of the energy difference of an electrical charge between two points. For household wiring the common junction between the ground rod and the bonded neutral wire is the point taken as the "zero" point. Of course, if you are measuring between two zero points any appreciable distance apart the effects of natural telluric variations in voltage and current flow will become apparent.

Is your resolution good enough to map small volumes or areas? If it is, it offers a method to actually test grounding/earthing systems.
With that kind of data available, NEC could produce code that actually makes sense.
Code inspectors could approve or deny grounding systems based on actual data.

 

[Warpspeed]

Grounding is just a concept, and it means different things in different situations.

Its like the concept of something being level.
So your builder uses a spirit level to lay out a floor or foundations for a building.
Another builder a thousand miles away also has another spirit level that will settle at a rather different angle (the Earth is not flat).

To ground something in an aircraft, onto the metal frame, is just as valid as driving a metal stake into the actual ground.

Even something hand held like a calculator or mobile phone has an internal "ground", usually battery negative.

So grounding is just a local frame of reference that you decide will be zero voltage, against which other voltages can be measured or compared.

 

[CoolWill]

Is your resolution good enough to map small volumes or areas? If it is, it offers a method to actually test grounding/earthing systems.
With that kind of data available, NEC could produce code that actually makes sense.
Code inspectors could approve or deny grounding systems based on actual data.

There are several things the NEC drops the ball on, but grounding and bonding isn't one of them, by and large. Besides using the single term "ground" to refer to both grounding and bonding, NEC 250 is a very solid section of the code.

 

[zanydroid]

I thought the conventional wisdom in electrician land is that actual data is harder to get than to just overkill on ground rod depth and dig/drive a little more. Because you would either need to get some precision measuring equipment or get some geology and engineering done.

Unless you can use modeling to justify some simpler rules of thumb.

 

[CoolWill]

Grounding is just a concept, and it means different things in different situations.

Its like the concept of something being level.
So your builder uses a spirit level to lay out a floor or foundations for a building.
Another builder a thousand miles away also has another spirit level that will settle at a rather different angle (the Earth is not flat).

To ground something in an aircraft, onto the metal frame, is just as valid as driving a metal stake into the actual ground.

Even something hand held like a calculator or mobile phone has an internal "ground", usually battery negative.

So grounding is just a local frame of reference that you decide will be zero voltage, against which other voltages can be measured or compared.

The electrical regulations used in the US make the mistake of referring to conductors used to equalize potential between non-current carrying metal parts or conductors that carry fault current as "equipment grounding conductors". It's true that those conductors are also connected to earth ground somewhere upstream as well, but it has lead many to misunderstand how exactly that little green wire in the cord does what it does.

 

[Warpspeed]

The electrical regulations used in the US make the mistake of referring to conductors used to equalize potential between non-current carrying metal parts or conductors that carry fault current as "equipment grounding conductors". It's true that those conductors are also connected to earth ground somewhere upstream as well, but it has lead many to misunderstand how exactly that little green wire in the cord does what it does.

"Grounding" can have more than one intended function, such as reduction of electrical noise and mutual interference between high power and sensitive circuitry, as well as the electrical safety ground we are discussing here.

Code, is manly about electrical safety, and the sometimes rather oddly worded requirements are all based on very sound well thought out electrical principles.
Other requirements such as EMC (electro magnetic compatibility) are a quite different matter and have some very different requirements.

Safety grounds are required to reliably carry high fault currents, but only for a short time, long enough time to trip/blow whatever isolates the over current circuit protection.
A secondary requirement, is to hold exposed accessible metal parts at very near ground potential in the event of low leakage current between active and the exposed metal that might produce a potential shock hazard.

All these mysterious rules and regulations have evolved over time, usually as the result of coroners inquests after death by electrocution of some unfortunate victim. Its just as important to understand the reasons why, and the philosophy behind the rules and the regulations, as just blindly attempting to comply without any understanding may create a potential future danger you may not have thought of.

 

[Checkthisout]

I dunno if it's worth saying but Ground and Ground Rods often get mixed up.

People think the EGC is there to dissipate electricity into the ground via the ground rod etc.

Here is a good one. Without a driven ground rod, can I still get shocked if I only touch a hot conductor? If the answer is yes then aren't ground rods causing an unnecessary safety hazard by allowing the earth to act as a neutral?

 

[hwy17]

then aren't ground rods causing an unnecessary safety hazard by allowing the earth to act as a neutral?

I know you're already hinting at this, but it was indeed considered a safety benefit of an IT grounded 3 phase service as used in say old rural connections in Finland. Couldn't get shocked by touching any single phase conductor and ground!

Afaik the justification for why that isn't safe, is nobody will notice the first phase to ground fault and it's likely to happen somewhere eventually. And then you have an unintentionally grounded conductor and two phase to ground shock hazards. So I guess from there the logic is you might as well ground one on purpose and then design everything else around the devil you know.

 

[hwy17]

Would there be any limitation on IT grounding a split phase service? I suppose not but I'm fuzzy on it. I think it's just coincidental that afaik only 3 phase services have ever been commonly IT grounded.

 

[Samsonite801]

Grounding is just a concept, and it means different things in different situations.

Its like the concept of something being level.
So your builder uses a spirit level to lay out a floor or foundations for a building.
Another builder a thousand miles away also has another spirit level that will settle at a rather different angle (the Earth is not flat).

To ground something in an aircraft, onto the metal frame, is just as valid as driving a metal stake into the actual ground.

Even something hand held like a calculator or mobile phone has an internal "ground", usually battery negative.

So grounding is just a local frame of reference that you decide will be zero voltage, against which other voltages can be measured or compared.

Yeah, Earth is just a common larger reference point, more info here about grounding vs earthing (with comparison chart)...

Difference between Earthing and Grounding with its Definition

Earthing and grounding are similar terms. Still, these are having many differences. The main difference between earthing and grounding is that the earthing refers that the circuit is physically connected to the ground with Zero Volt Potential.

www.toppr.com