Service Entrance Grounding

[Jamesco]

View attachment 19779I am reviewing some specs and came across this section. I was wondering what you all thought of creating a loop with the grounds and connecting the ends back together, like the state is suggesting. It is not a configuration that I am familiar with. I am new to the field, but I know that a grounding system can and-- in an industrial setting-- generally does have some amount of current on it. By creating this loop, would you be degrading and making a less efficient system? I mean, because the path of least resistance is a loop? Also, what implications would this have for cathodic protection and the degradation of components (lugs, cables, and such) over time?
Thanks for any insights and opinions.
--Nate

Just a guess on my part the EE spec'd the GEC loop for redundancy.

Maybe his thinking, the continuous GEC closed loop will provide a better path for a direct lightning strike to travel to earth through the 3 ground rods. If you know the EE, and you don't think he would be offended, why don't you just ask him why. If you ask him, and he gives you a reply, please post back what he says.

 

[Jamesco]

Maybe it is because the EE does not understand grounding and is simply repeating what 'granddad did'. Just because an EE asks for it does not make it automatically a good or bad design.

Just because an EE asks for it does not make it automatically a good or bad design.

Not for you or me to say. It's in the specs.

 

[Jamesco]

When it comes to The Ground there a lot of people who come up with a lot of things that don't make sense.

According to you.

 

[electrofelon]

According to you.

....And many other very knowledgeable and experienced people, and electrical theory.

 

[johnwhitcraft]

NEC Art 250.56 Resistance of Rod, Pipe, and Plate Electrodes

NEC Art 250.56 Resistance of Rod, Pipe, and Plate Electrodes

Just a guess on my part the EE spec'd the GEC loop for redundancy.

Maybe his thinking, the continuous GEC closed loop will provide a better path for a direct lightning strike to travel to earth through the 3 ground rods. If you know the EE, and you don't think he would be offended, why don't you just ask him why. If you ask him, and he gives you a reply, please post back what he says.

Consider that this might just be a belt and braces approach to specifying the Grounding Electrode System: What If the designer has to assume no ground electrodes exist and the surrounding terra is sand or some other poor earth conductor? Also, What If the designer has to assume installer has no means to guarantee the resistance to ground is 25 ohms or less?

 

[Jamesco]

Consider that this might just be a belt and braces approach to specifying the Grounding Electrode System: What If the designer has to assume no ground electrodes exist and the surrounding terra is sand or some other poor earth conductor? Also, What If the designer has to assume installer has no means to guarantee the resistance to ground is 25 ohms or less?

Also, What If the designer has to assume installer has no means to guarantee the resistance to ground is 25 ohms or less?

NEC doesn't say the ground resistance shall be 25 ohms or less.

NEC doesn't even say the ground resistance has be measured. It just says if it is measured and it measures over 25 ohms it shall be supplemented by one additional ground rod. You're done, a second ground resistance measurement is not required. The initial ground resistance reading could have been 265 ohms. What do you think it would be with the additional ground rod?

https://www.youtube.com/watch?v=Yg6G5VUSsWA

 

[kwired]

NEC doesn't say the ground resistance shall be 25 ohms or less.

NEC doesn't even say the ground resistance has be measured. It just says if it is measured and it measures over 25 ohms it shall be supplemented by one additional ground rod. You're done, a second ground resistance measurement is not required. The initial ground resistance reading could have been 265 ohms. What do you think it would be with the additional ground rod?

https://www.youtube.com/watch?v=Yg6G5VUSsWA

And that 25 ohm rule is only for rod, pipe or plate electrodes, other electrode types don't require measuring or supplemental electrodes other then water pipe - but that is because of the common practice of replacing water pipes with non metallic piping more so then water pipes having high resistance to earth.

 

[Jamesco]

And that 25 ohm rule is only for rod, pipe or plate electrodes, other electrode types don't require measuring or supplemental electrodes other then water pipe - but that is because of the common practice of replacing water pipes with non metallic piping more so then water pipes having high resistance to earth.

And in the case where a home has a plastic water line the only grounding electrode is a ground rod(s). And the ground resistance could very well be 265 ohms, or more. Who measures ground resistance for a house? Nobody that I know of.

Can there be electrical problems during thunderstorms? Do you know of anyone that has lost a TV during a thunderstorm? How about an appliance with a micro processor? Do you know of anyone? Maybe yourself?

 

[kwired]

And in the case where a home has a plastic water line the only grounding electrode is a ground rod(s). And the ground resistance could very well be 265 ohms, or more. Who measures ground resistance for a house? Nobody that I know of.

Can there be electrical problems during thunderstorms? Do you know of anyone that has lost a TV during a thunderstorm? How about an appliance with a micro processor? Do you know of anyone? Maybe yourself?

Does having an electrode with less then 25 ohms assure you you won't have problems due to lightning?

I think I have picture somewhere of electrical equipment on a grain bin, something that is naturally well grounded just because of how they are designed, that got destroyed in a lightning incident.

 

[Jamesco]

Does having an electrode with less then 25 ohms assure you you won't have problems due to lightning?

I think I have picture somewhere of electrical equipment on a grain bin, something that is naturally well grounded just because of how they are designed, that got destroyed in a lightning incident.

Who said anything about a direct hit? Not Me.:happysad:

 

[al hildenbrand]

And in the case where a home has a plastic water line the only grounding electrode is a ground rod(s). And the ground resistance could very well be 265 ohms, or more. Who measures ground resistance for a house? Nobody that I know of.

Can there be electrical problems during thunderstorms? Do you know of anyone that has lost a TV during a thunderstorm? How about an appliance with a micro processor? Do you know of anyone? Maybe yourself?

This is getting pretty far afield of the OP question about the value of three ground rods connected by a continuous Grounding Electrode Conductor installed in a loop with both ends inside the same raceway.

Your opinion is that it is to be done because it is in the specs.

My opinion is that it is a waste of labor and material and has no NEC basis nor does it have any consensus theoretical basis.

There are other opinions that have been offered.

Lightning electromagnetic pulse and effects of direct hits are so complex, with respect to a Premises Wiring (System) AND all of the conductive material of a structure, as to be of no value in arguments about the value of a ground rod connection to Earth at the Service Disconnect, in my opinion. One can only say that a ground rod "may" help mitigate a lightning caused electrical event in a Premises Wiring (System).

 

[ActionDave]

And in the case where a home has a plastic water line the only grounding electrode is a ground rod(s). And the ground resistance could very well be 265 ohms, or more. Who measures ground resistance for a house? Nobody that I know of.

There is no reason to.

Can there be electrical problems during thunderstorms? Do you know of anyone that has lost a TV during a thunderstorm? How about an appliance with a micro processor? Do you know of anyone? Maybe yourself?

So what? The size of your ground rods isn't going to make any difference.

 

[Jamesco]

There is no reason to.

So what? The size of your ground rods isn't going to make any difference.

Correct, a 2ft x 8ft ground rod won't make that much difference than a 5/8" x 8ft ground rod. Yuuup you are correct!

 

[Jamesco]

This is getting pretty far afield of the OP question about the value of three ground rods connected by a continuous Grounding Electrode Conductor installed in a loop with both ends inside the same raceway.

Your opinion is that it is to be done because it is in the specs.

My opinion is that it is a waste of labor and material and has no NEC basis nor does it have any consensus theoretical basis.

There are other opinions that have been offered.

Lightning electromagnetic pulse and effects of direct hits are so complex, with respect to a Premises Wiring (System) AND all of the conductive material of a structure, as to be of no value in arguments about the value of a ground rod connection to Earth at the Service Disconnect, in my opinion. One can only say that a ground rod "may" help mitigate a lightning caused electrical event in a Premises Wiring (System).

...

 

[infinity]

I know that people get all warm and fuzzy over ground rods but wouldn't a high quality surge protective device installed at the panel be a better option?

 

[Jamesco]

I know that people get all warm and fuzzy over ground rods but wouldn't a high quality surge protective device installed at the panel be a better option?

Thank you. I have been waiting for someone to post that question.

https://www.mtl-inst.com/images/uploads/AN_904-1003_Rev_G.pdf

 

[ActionDave]

Thank you. I have been waiting for someone to post that question.

https://www.mtl-inst.com/images/uploads/AN_904-1003_Rev_G.pdf

From the link you posted

7.6.2 Recapitulation

For protecting a single installation, a very low ground
impedance is not necessary.

A multi-installation as a whole will benefit from low ground
impedance.

There is no magic figure for an acceptable level of ground
impedance.

The ground impedance achieved will in many cases be
determined by the characteristics of the ground and available
time and funds

 

[kwired]

All a surge protector does it try to equalize voltage (anything over it's clamping voltage) across the lines it is connected to. A lightning surge is likely seeking ground - so the bulk of the current through the surge protector in that incident is probably being directed to the grounded conductor. If the surge is coming in on the grounded conductor - then the protector doesn't really do much in that incident.

 

[Jamesco]

All a surge protector does it try to equalize voltage (anything over it's clamping voltage) across the lines it is connected to. A lightning surge is likely seeking ground - so the bulk of the current through the surge protector in that incident is probably being directed to the grounded conductor. If the surge is coming in on the grounded conductor - then the protector doesn't really do much in that incident.

It can't just sit there on the grounded conductor. It's looking for mother earth.

From IEEE 62.72:

“The importance of ensuring that the grounding system provides a low earth impedance, and not simply a low earth resistance, must be understood. A spectral study of the typical waveforms associated with transient impulses, such as those characteristic of lightning and switching surges, reveals both high-frequency and low-frequency components. The high-frequency component is associated with the extremely fast rising “front” of the transient (typically less than 10 μs to peak current), whereas the low-frequency component resides in the long “tail” or follow-on current of the decaying impulse. High-frequency components are significant for inductive effects (induced voltages in the circuits), whereas low-frequency components are significant for energy effects (deposited energy in resistive elements).”


If an SPD is connected to ground and is expecting ground to be part of its dissipative path, the ground system must be taken into account. It also means the grounding system must be verified as a low resistive and low impedance path.

http://www.nemasurge.org/grounding/

 

[al hildenbrand]

It can't just sit there on the grounded conductor. It's looking for mother earth.

If your statement is a generalization, it is not accurate. If "it" is from an ElectroMagnetic Pulse (EMP), ANY conductive path that has less than optimal orientation to the EMP is also an available path for "it" to travel through.

"It" takes ALL available paths.