Ignorant questions from "quallified persons"

[davedottcom]

My stupid question

My stupid question

I guess the rep had never been to Chicago before.

Here's my stupid question...I've heard of the wiring practices enforced in Chicago for years now... were these practices brought about after the "big fire" as an attempt to never repeat such a disaster?

 

[iwire]

The GEC serves many functions, but lightning is far from its primary purpose.

OK, here is your chance, tell us what is the GECs primary purpose.

And if it would not be to much trouble could you provide some references?

 

[Al Pike]

Building inspector

Building inspector

Thought that I should install a bonding screw in my sub panel being that they only cost a couple of cents. I said nothing and called his company and refused to have him inspect any of our jobs.

 

[mivey]

Thought that I should install a bonding screw in my sub panel being that they only cost a couple of cents. I said nothing and called his company and refused to have him inspect any of our jobs.

I like the low material cost philosophy that you can just do whatever. You can take your bolt cutters and cut the grounded conductor in half since that would require zero added material!

 

[zog]

Just what makes a person "qualified" in any trade?

According to the NFPA 70E, a ?Qualified Person" is one who is trained and knowledgeable of the construction and operation of the equipment or the specific work method, and be trained to recognize the hazards present with respect to that equipment or work method.

Such persons shall also be familiar with the use of the precautionary techniques, personal protective equipment, insulating and shielding materials, and insulated tools and test equipment. A person can be considered qualified with respect to certain tasks but still be unqualified for others.

An employee that is undergoing on the job training and who, in the course of such training, has demonstrated the ability to perform duties safely at his or her level of training and who is under the direct supervision of a qualified person shall be considered to be a qualified person for the performance of those duties.

In addition, to be permitted to work within the limited approach of exposed energized conductors and circuit parts the person shall be trained in all of the following:
Qualified employees shall be trained and competent in:
?The skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment
?The skills and techniques necessary to determine the nominal voltage of exposed live parts
?The minimum approach distances specified in this section corresponding to the voltages to which the qualified employee will be exposed, and,
?The decision making process necessary to determine the degree and extent of the hazard and the personal protective equipment and job planning necessary to perform the task safely

A few notes (From Zog) to add to the 70E definition.
?Only the employer can deem an employee qualified after they have had the proper training and have demonstrated profinency using the skills and method learned.
?There is no such thing as NFPA 70E certification, going to a training course does not make an employee qualified.
?The most misunderstood part of the "qualified" term is that it is all emcompassing, you are "qualified" to work on a specific type or piece of equipment.
?Neither a J-card, a masters license, or an engineering degree make you a "qualified person"
?The word "electrician" is not anywhere in the definition of a "qualified person" meaning these rules apply to all employees and you dont have to be an electrician to be "qualified"

 

[zog]

As an instructor for 15 years, training EE's and electricians that have been in the trade for 10, 20, 30 years (Had one 50 year guy) I stopped being shocked by questions like this a long time ago. But the only stupid question is the one you don't ask.

 

[kwired]

Why do so many electricians here repeat this without taking the time to really think this over? You've been sold on this concept, and no one bothers to question the validity of it. Of the functions of the GEC, lightning is one of the more trivial aspects.

• If there is a direct strike on a building, the GEC isn't going to protect a single thing.The entire electrical system is still going to be elevated to a huge voltage.
• If you think the lightning is going to follow the grounding system and go out through the ground rod, thankfully it doesn't, because it would damage that much more of the structure as it traveled from the point of entry to the GEC.
• Is lightning selective? If it strikes a building, is it only going to follow the green colored wires? (If you are about to say it wants to find a path to ground (zero volts) 120 volts is pretty trivial in the general scheme of things and constitutes a fraction of an inch worth of spark gap.)
• If the lightning strike was nearby but not a direct strike, the GEC is going to experience an elevated voltage and actually carry it into the premises.
• If the strike is on the utility, the premises wiring is still going to be elevated and the premises GEC won't protect a thing.
• If the primary purpose of the GEC was for lightning, then it wouldn't matter if the resistance to earth was 25 ohms or 2500 ohms. There would be no voltage difference without current flow, and once current flows in a lightning strike, resistance is meaningless because plasma is the current carrying conductor.

The GEC serves many functions, but lightning is far from its primary purpose.

You have mentioned many facts about lightning and I agree with you on most of them. You did not disprove my comment about the primary function of a grounding electrode being for lightning, and never mentioned any other reason why grounding elecrodes should be used.

250.4 (A)(1) says it pretty well:

(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

A grounding electrode system is not insurance there will be no damage in a lightning event, but it may help divert the current to a safer path. The better the path the more current will be diverted to it. Direct lightning strikes will have lots of damage, surge current in the system from a nearby strike may all be diverted to grounding electrode.

OK, here is your chance, tell us what is the GECs primary purpose.

And if it would not be to much trouble could you provide some references?

I had a call to a small farm house several years ago that had a fire in the kitchen that started right after a nearby lightning strike. The fire started behind the range.

The range was a gas range with copper tubing used as the gas line. This tubing was electrically continuous and direct buried from the house to a propane tank maybe 50 - 75 feet away from the house. Behind the range there was also a 50 amp receptacle for an electric range that was not in use but was connected and available for use. It was in very close proximity to the gas line.

We figured that the ligntning likely entered the home through the electric service, noted that there was no grounding electrode connected to the service, and it likely arced from the grounded conductor in the range receptacle (older 3 wire circuit) to the gas line that was a good electrode because it was buried to the tank.

I can not say that a proper grounding electrode would have prevented this event, but it certainly would have had a better chance of carrying enough current to prevent what did happen.

 

[iwire]

I really have no idea what the primary purpose of a GEC is at a typical building or structure. If the primary purpose of the GEC is lightning protection it does a really bad job of it. But just what is a typical GEC good at?

What is it's primary purpose?

Has it's primary purpose changed since it was first required and now?

Besides being arrested, what would happen if I removed all the GECs in a two mile radius of my home?

 

[Rick Christopherson]

I really have no idea what the primary purpose of a GEC is at a typical building or structure. If the primary purpose of the GEC is lightning protection it does a really bad job of it. But just what is a typical GEC good at?

What is it's primary purpose?

It wasn't my intention of pointing out what the primary purpose of the GEC was...that's what leads to discussions such as this in the first place. What I was pointing out is that many posters here tend to "pigeonhole" its purpose as being just for lightning. Considering how poorly it actually serves this purpose is a good indication that it really isn't the primary purpose.

I don't believe there is any single "primary" purpose, and that is why I am hesitant about listing some of its other functions for fear it would be construed as suggesting any of them are primary.

In a similar vein, it is also the reason why I oppose the strong distinction between GEC and EGC. These two parts of an electrical system share common functions, and when they are thought of as being separate components (in a person's own mind) it tends to cause them to think more of one function and less of the other.

Even though I just said I was hesitant about doing this, one of the functions of the GEC that I think about most often is for maintaining a voltage reference to the nearby environment. This particular function is where the GEC and EGC share the same purpose.

Besides being arrested, what would happen if I removed all the GECs in a two mile radius of my home?

I like this question. Removing all GECs in a 2 mile radius would imply also removing the GECs from one or more levels of POCO transformers too. Here is where the voltage reference would become most significant.

For the sake of argument, let's assume you have 12kV on the primary side of a transformer, and 120/240 on the secondary, but there is no GEC on the secondary side. This means that the secondary is floating with no reference beyond the magnetic coupling of the transformer itself. The voltages between the secondary taps will always remain 120/240 relative to each other, but their voltages relative to earth can be anywhere from 0 to 12kV, based on the limitations of the primary side voltage.

Bring this power into your home and you suddenly have the possibility of having 11.9kV (12k-120v) between your center-tap (neutral) and the physical earth your house is built on. Of course this voltage is bled off very quickly at the first hint of a G-N bond, but the energy necessary to bring the 11.9kV down is not trivial for the short instant, nor does it ever vanish completely.

 

[iceworm]

xxx In a similar vein, it is also the reason why I oppose the strong distinction between GEC and EGC. These two parts of an electrical system share common functions, and when they are thought of as being separate components (in a person's own mind) it tends to cause them to think more of one function and less of the other. xxx.

Rick - you really need to read the definitions of Equipment Grounding Conductor and Grounding Electrod Conductor in article 100

NEC 2008
Grounding Conductor, Equipment (EGC). The conductive
path installed to connect normally non–currentcarrying
metal parts of equipment together and to the system
grounded conductor or to the grounding electrode
conductor, or both.
FPN No. 1: It is recognized that the equipment grounding
conductor also performs bonding.
FPN No. 2: See 250.118 for a list of acceptable equipment
grounding conductors.

Grounding Electrode Conductor. A conductor used to
connect the system grounded conductor or the equipment to
a grounding electrode or to a point on the grounding electrode
system.

ice

 

[glene77is]

iWire,
I want to hear what you have to say,
so here is a stab.

If the primary purpose of the GEC is lightning protection

IMO, it provides a shunt Reference for a lightning impulse.

Lightning is between the sky/clouds and the real-earth ground,
largely a capacitively-coupled charge build-up.

The GEC provides a first line defense against lightning damage
by providing a shunt-path for the high-frequency lighting pulse (positive or negative)
between the POCO Service and the real-ground (earth).
The GEC is a shunt for the capacitively coupled voltage charge
built-up between the sky/clouds and the real-earth.

There is a secondary function relating to referencing POCO high voltage 60 Hz
to the POCO ground-return system.

I always invite your comments, Bob.

it does a really bad job of it.

Just your Opinion. You need a reference.
You probably have an example ready and waiting.

But just what is a typical GEC good at?
What is it's primary purpose?

? Lightning reference into the real-earth ?
? Connection into the POCO ground-return system ?

Has it's primary purpose changed since it was first required and now?

Bob, this sounds you will provide an interesting historical answer!

I always invite your comments, Bob. {^,^}

 

[iceworm]

I really have no idea what the primary purpose of a GEC is at a typical building or structure. If the primary purpose of the GEC is lightning protection it does a really bad job of it. But just what is a typical GEC good at?

What is it's primary purpose?

Has it's primary purpose changed since it was first required and now?

Besides being arrested, what would happen if I removed all the GECs in a two mile radius of my home?

Interestingly, I have had the opportunity to have similar conversations with two nationally recognized code experts. One got upset with me. The other just blew me off. I think the current code, 250.4.A.1, reads the way it does is because the Wisemen of Gotham have spoken and they don?t have an easy way to back down. I think the wide spread use of utility MGN in the US is because it saved dollars on the original distribution installation. And now they don?t have any easy way to get out of it. It would cost us to much, And yes, it will be us paying the bill ? it should be us paying, we are the ones using the electricity.

The Germans and French figured it out. But that is because they had to. Their distribution systems and building were bombed to oblivion.

I don?t know why the Norwegians figured it out ? maybe they are just smarter than we are

ice

 

[iceworm]

I really have no idea what the primary purpose of a GEC is at a typical building or structure. If the primary purpose of the GEC is lightning protection it does a really bad job of it. But just what is a typical GEC good at?

What is it's primary purpose?

Has it's primary purpose changed since it was first required and now?

Besides being arrested, what would happen if I removed all the GECs in a two mile radius of my home?

Caution ? rant to follow. Recommend: Delete before reading.

(2008) 250.4.A(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

I really have no idea what the primary purpose of a GEC is at a typical building or structure. xxx

Has its primary purpose changed since it was first required and now? xxx

I don?t either. I don?t know. Thirty years ago I knew exactly what the NEC was talking about in 250.4. 15 years ago I realized I was unclear about some of the terms. About 5 years ago I realized I didn?t have a clue about most of this statement.

I no longer know what a ?line surge? is. (Yes, I know what a switching transient is). This one completely looses me. I have this picture in my mind of a Far Side cartoon. The guy is standing next to his house. The house is covered in electrically arcing slime. He is watching the transmission line and sees a fat lump coming down the line toward him and says, ?Damn, here comes another surge.?

I don?t know how this house ground will limit ?voltage imposed by lightning?. If a strike hits the transmission line near to your house transformer, it will pick the line and MGN up to maybe 50kV ? 100kV, with a high frequency impulse. And since it picked up the MGN, your house system, which has the house neutral tied directly to the MGN, also goes up to 50kV. And eventually the energy will drain off to the earth. And maybe your house will still be there. I don?t know what the house ground did to help that the MGN did not already do. Maybe if it were installed per NFPA780 it would help ? but the house grounds are not.

This ?stabilize the voltage to earth during normal operation? also completely leaves me blank. Your house system is sitting above earth potential by the amount the MGN is above earth. The further you are from the substation, the higher it will be ? 2V, 4V, 6V, 8 ? Who do we appreciate ? The Utility!! So you pull the ground rod and measure the house neutral to earth potential ? and it is still the same as it was with the ground rod. Color me confused.

As for the ?unintentional contact with higher-voltage lines?, this is getting too long, so I?ll leave that for later, but I don?t think a house gorund connected to the house neutral helps much.

xxx Besides being arrested, what would happen if I removed all the GECs in a two mile radius of my home?

First, you would deprive the utility of all of the free ground rods that their system uses.

Second, If the house is in an urban area, and has a nice metallic waterline connected to the water main and all of the neighbors metallic water systems, then you deprive your unbalanced neutral current of a parallel path back the utility transformer,


****************************
Personally ? I think every house should have a ronk blocker and a decent lightning arrestor at the utility transformer. Install a CEE all the way around the house foundation and bond the house system neutral to that.

Will this fix all the current crop of evils? Likely not. But it should fix a bunch.

So sayeth the worm

 

[glene77is]

... Understanding basic electrical theory
makes much of the code make more sense also.

There are too many installers and not enough electricians.

... In service work a little theory makes a big difference in productivity.

kWired,
You are three rungs up the ladder from most everybody else.

 

[Rick Christopherson]

Rick - you really need to read the definitions of Equipment Grounding Conductor and Grounding Electrod Conductor in article 100

I know what the definitions are. This isn't about reading code. Understanding electrical information is not about being able to cite code, it is about knowing the reasons why code says what it says.

Sorry for the short response, but I have to run.

 

[George Stolz]

Even though I just said I was hesitant about doing this, one of the functions of the GEC that I think about most often is for maintaining a voltage reference to the nearby environment.

Answer:

This “stabilize the voltage to earth during normal operation” also completely leaves me blank. Your house system is sitting above earth potential by the amount the MGN is above earth. The further you are from the substation, the higher it will be – 2V, 4V, 6V, 8 – Who do we appreciate – The Utility!! So you pull the ground rod and measure the house neutral to earth potential – and it is still the same as it was with the ground rod.

Exactly. The GEC and GES do not change the reference to remote earth.

For the sake of argument, let's assume you have 12kV on the primary side of a transformer, and 120/240 on the secondary, but there is no GEC on the secondary side. This means that the secondary is floating with no reference beyond the magnetic coupling of the transformer itself.

Wrong. The neutral on the primary side is tied to the secondary side, hence the stray voltage that Iceworm was referring to.

Caution – rant to follow. Recommend: Delete before reading.

Look out boys, he's onto us. :grin:

As for the “unintentional contact with higher-voltage lines”, this is getting too long, so I’ll leave that for later, but I don’t think a house gorund connected to the house neutral helps much.

I disagree. When you think of the earth as the EGC for the utility, the mass of grounding helps to blow their fuses in the event of a fault. A single service with a 25Ω ground rod means poodly-squat, but you get an entire neighborhood working together in parallel and they will help provide that return path for that 12kV fault, IMO.

I know what the definitions are. This isn't about reading code. Understanding electrical information is not about being able to cite code, it is about knowing the reasons why code says what it says.

Ahh, but if the code started on a questionable premise, now all we are doing is rationalizing those codes, are we not?

 

[mivey]

I really have no idea what the primary purpose of a GEC is at a typical building or structure. If the primary purpose of the GEC is lightning protection it does a really bad job of it.

Using "GEC" as a surrogate term for the earth connection, most individual earth connections does not do a very good job at it by themselves because they are not designed to. Most of the connections are part of a larger system of connections. This system of connections is what is supposed to do the "good" job. There are few real protections from a direct hit but rather attempts to reduce the impact from hits in general.

But just what is a typical GEC good at?

Providing a path to Mother Earth

What is it's primary purpose?

Prevent excessive voltages (lightning and other transients) and to limit & stabilize the voltage to ground.

Has it's primary purpose changed since it was first required and now?

I'm sure it has as the understanding of grounding and bonding has changed a lot over the years.

Besides being arrested, what would happen if I removed all the GECs in a two mile radius of my home?

One dramatic effect (assuming you are talking about isolating from the POCO as well) would be to get rid of the issue the power company imposes on everybody by using the earth as a return current path. This often causes trouble-some neutral-to-earth voltages and ground currents.

You add a problem by not giving the lightning and ground-related transients a defined path back to Mother Earth. But if you could install a proper shielding system: so what?

If you could remove all the grounds, and isolate yourself, and shield yourself, you would be like an airplane in flight. If your power is not connected to your structure, you would need a system in place to detect faults to your structure (like with ungrounded delta systems).

 

[mivey]

Exactly. The GEC and GES do not change the reference to remote earth.

That is right. Adding another earthing connection to the neutral will not "pull it down" to remote earth.

But without connection to earth (assuming we can isolate the POCO neutral), the voltage of the secondary system to earth might be most anything.

I disagree. When you think of the earth as the EGC for the utility, the mass of grounding helps to blow their fuses in the event of a fault. A single service with a 25Ω ground rod means poodly-squat, but you get an entire neighborhood working together in parallel and they will help provide that return path for that 12kV fault, IMO.

Your opinion is correct.

 

[jumper]

Cool, this thread has finally gotten interesting.

 

[iceworm]

xxxAs for the ?unintentional contact with higher-voltage lines?, this is getting too long, so I?ll leave that for later, but I don?t think a house gorund connected to the house neutral helps much. xxx

xxx I disagree. When you think of the earth as the EGC for the utility, the mass of grounding helps to blow their fuses in the event of a fault. A single service with a 25Ω ground rod means poodly-squat, but you get an entire neighborhood working together in parallel and they will help provide that return path for that 12kV fault, xxx

xxx Your opinion is correct.

Let's take the case of a 139kv line in a substation dropping across the 7200V line going out to house transformers. The 7200V line goes to about 80kv ~ 11X7200. The house 240 suddenly jumps to 2600V. And we are waiting for the utility fuses to trip. -----

Still waiting -------

Still - ah there they go. It finally cleared. And most anything that was turned on in the house is toast. What did this house ground rod do? After the house equipment shorted the house main tripped unless the equipment burned open quicker than the main could open.

I don't see where the house ground rod made anything better.

Got to go to work for a while - I'll check back in later

ice