Grounding Electrode System NEC 250-50

[RUWired]

I don't think so, around here years ago all you needed was a 20 foot long piece of #4 bare copper under the footing or slab.

This # 4awg is the minimum size.Good for services with conductors up to 2/0 -3/0 cu.If service conductors are larger, then the GEC/CEE would be larger.This does'nt say maximum size,it says minimum.
Rick

 

[infinity]

I don't think so, around here years ago all you needed was a 20 foot long piece of #4 bare copper under the footing or slab.

This # 4awg is the minimum size.Good for services with conductors up to 2/0 -3/0 cu.If service conductors are larger, then the GEC/CEE would be larger.This does'nt say maximum size,it says minimum.
Rick

The conductor to the CCE isn't required to be larger than #4 CU. 200 amp, 2000 amp service or any larger service, #4 is the largest ever required.

 

[RUWired]

Trevor,I see it now 250.66 (C) allows a maximum #4.

 

[George Stolz]

I found the IAEI Article posted by peteo to be very interesting. Mr. Michael Johnson seems more than quilified to be able to state what the "intent" of the code is. To me anyway.

His name is Michael Johnston, member of CMP-5, which oversees Article 250 (among others). If you look at the 2005 ROP, he probably had the most proposals in to modify Article 250. Among them were the popular change to "Equipment Bonding Conductor" and the change of the name to "Grounding and Bonding." It's interesting to me that so many good ideas are rejected, even by one of their own.

Anyway, intent aside, the words must stand on their own. I agree with Johnston's read on the current text. I also believe it to be overkill.

 

[davidv]

Dear Bryan, Don
As for any incident, although, it does not have immediate damage to life or property, put in a different situation, it might.

Once upon my time, during a substation grounding rehab, replacing potrions of the buried 4/0 copper ground grid conductors taken by scavengers, on an unfenced old parts laydown area, away from the switchyard.
One of my men mistakenly removed his dirty gloves and cleaned the wires before making thermic weld connections, when suddenly he jerked his hands away from the wires. It became ?hot?. Realizing the yard is making some reclosing operations but barely notice the usual clacking sound due to the distance, we waited for a while. After voltmeter check, touch it again and sure enough the shock voltage was gone. We finished the job with rubber gloves on.

Another case is during HVAC testing & commisioning, of a two 500mcm parallel feeder for a 1000A Dy starter, A gap in the loose RSC coupling of one set is giving off sparks like weld machine, when chiller motor is running. Insulation resistance is high P-P & P-G, finally decided to pulled the cables, we noticed that one L1 & one L3 wire of both sets went in to different CT donuts meant for each of the 3phases, but was terminated correctly. Rewired it back properly and there, no more sparks,
Figured there was no real fault and suspecting it for ciculating currents induced by uncancelled cable fluxes, I purposely did not change the loose coupling, since I got time returned the original CT routing, and the sparks returned this time on couplings of both sets.
Replaced the oversized coupling intended for pvc conduit adapters some wisecracks used rewired again and re-tighten connections along with the bonding bushings.

From the grounding point of view, I?m convinced that the grounding system is doing its job of conducting these unwanted currents to be absorb by the earth, whatever the source maybe. Maybe ocassionally but I?m convinced that when properly made, its not sleeping out there.

So for those thinking that it is ?of little no or very minor importance? , go ahead, no one?s stopping them, but I will not certainly buy that either.

davidv
es

 

[iwire]

One of my men mistakenly removed his dirty gloves and cleaned the wires before making thermic weld connections, when suddenly he jerked his hands away from the wires. It became ?hot?. Realizing the yard is making some reclosing operations but barely notice the usual clacking sound due to the distance, we waited for a while. After voltmeter check, touch it again and sure enough the shock voltage was gone. We finished the job with rubber gloves on.

A 'better' connection to earth would not have made a difference here.

Another case is during HVAC testing & commisioning, of a two 500mcm parallel feeder for a 1000A Dy starter, A gap in the loose RSC coupling of one set is giving off sparks like weld machine, when chiller motor is running. Insulation resistance is high P-P & P-G, finally decided to pulled the cables, we noticed that one L1 & one L3 wire of both sets went in to different CT donuts meant for each of the 3phases, but was terminated correctly. Rewired it back properly and there, no more sparks,

Again a 'better' connection to planet earth would not have made a difference.


In both these cases only better bonding through metallic paths back to the source would have changed the results.

No electrical 'connection' to dirt would have changed the events you described.

 

[don_resqcapt19]

David,

From the grounding point of view, I?m convinced that the grounding system is doing its job of conducting these unwanted currents to be absorb by the earth, whatever the source maybe.

For current to flow there must be a complete circuit, unless the earth is generating the current in question, it cannot be returned to the earth. It must return to its original source.
Don

 

[davidv]

Thats nice, Bob I agree, with you, as well as with Don , Bryan, George
same as my previous replies GES is not meant to Save life or property.
Shutting the source will, putting them back to the source is one good method,but treating it with such insignificace is not what I like or feel like.( pls. dont bother with my preferences, its un-important)
Putting it away is another, that is for those non ordinary conditions.
As for letting transients in to a source is not a good idea, becoz its sources are not clearly defined.
I'm not trying to convince anyone to my opinion, (what makes me think I can?) just sharing my views so that this forum wont sound like a MH chorus line.

davidv
es

 

[bphgravity]

I'm not saying anyone is right or wrong. All I am saying is that just about every other aspect of our code has an event or situation that was established as substantiation for the code to exist. It seems the whole grounding idea was nothing more than a huge compromise.

Mr. Ufer performed a great experiment that proved concrete encased electrodes have a consistently low resistance over its life yet what did this prove? Over 40 years of research yet no indication for the exact reason an electrical service needs or requires such low resistance grounding.

Almost everything attributed to grounding is actually a result of bonding yet so much emphasis is placed on the methods and procedures for grounding. So much time, labor, and materials are put into establishing a GES and for what - a possible lightning strike or a possible transformer fault? It just seems like the more the history of grounding is discovered with the lack of research or data supporting grounding, it?s no wonder many of us are becoming critical of the idea.

 

[davidv]

Don,

For current to flow there must be a complete circuit, unless the earth is generating the current in question, it cannot be returned to the earth.

The earth is a source & sink for all energy forms, sizing its reaction depending on the energy coming to it, not a conductor. it is part of the whole energy circuit, currents can be returned

It must return to its original source.

I agree, thats what those EGCs are for
david

 

[davidv]

Bob:
Bob Quoted "No electrical 'connection' to dirt would have changed the events you described"

Yes, true, expecting the GES to change things will only get you disappointed. As Bryan said its a huge compromise. Its a contingency provided for the unexpected, doesnt mean it should be made less.

davidv
es

 

[ryan_618]

Back to the original question, I was talking to the UL rep on panel 5 about this, and he said that the intent is that at least one of each electrode type is to be used. I realize this is not a formal interpretation, however. He also stated that they are hoping to clear this up for the 2008 cycle.

 

[don_resqcapt19]

David,

The earth is a source & sink for all energy forms, sizing its reaction depending on the energy coming to it, not a conductor. it is part of the whole energy circuit, currents can be returned

The only time that currents can be returned via the earth is the cases where the source circuit has another connection to the earth. If there is no second connection, there is no path and there is no current flow. The earth is not a sink or a source of energy.
Don

 

[petersonra]

I don't think so, around here years ago all you needed was a 20 foot long piece of #4 bare copper under the footing or slab.

Right. The point is what if there is more than one "footing or slab"?

The requirement is to use all of the available types of electrodes. The type of electrode is described in 250.52(A)(1)-(6). If a building had multiple buried water pipes would you be required to use all of them?

it does not say each type in 250-50. One could argue it is implied though.

250.50 Grounding Electrode System. If available on the
premises at each building or structure served, each item in
250.52(A)(1) through (A)(6) shall be bonded together to
form the grounding electrode system. Where none of these
electrodes are available, one or more of the electrodes
specified in 250.52(A)(4) through (A)(7) shall be installed
and used.

 

[petersonra]

Here I go with my nitpicking again. :lol: If we are talking about AC systems, we really should be saying "impedance" instead of "resistance."

I know, it's a minor issue to some, and we all know what is being said when we hear "resistance." I also realize that capacitave and inductive effects are usually not an issue at 60 HZ. But impedance is technically correct, and resistance is not.

250.56 specifically uses the word resistance.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(2) through (A)(7). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.

 

[peter d]

250.56 specifically uses the word resistance.

So? Just because the NEC is using incorrect terminolgy, that doesn't change the fact that it's still impedance.

The NEC should be revised then.

I make a big deal out of this because we must be technically correct when having these discussions and arguments.

 

[iwire]

The earth is a source & sink for all energy forms, sizing its reaction depending on the energy coming to it, not a conductor. it is part of the whole energy circuit, currents can be returned

I don't mean to be rude and perhaps I am just misunderstanding you.

But the earth is not a sponge for 'spare' electrons.

It is not an electrical sink.

 

[sandsnow]

hey guys

I didn't see this mentioned. 250.4(A)(1) partial Code quote:

....that will stabilize the voltage to earth during normal operation.

Sounds pretty important, though I will admit I don't understand the theory behind.
I'm not trying to argue for the GES, just asking the question how important is the "stabilization" and a short idea of how that works.

Number two. Ungrounded systems still require a connection to an electrode. The explanation I was given was that capacitance will cause a static charge to build up and the connection to earth dissipates that.
Now my theory could be way off and use of terms, but I believe someone here told me that.

I will have to throw in behind Bryan that we seem to ground based on tradition. The old"but we've always done it that way"!!!

 

[petersonra]

250.56 specifically uses the word resistance.

So? Just because the NEC is using incorrect terminolgy, that doesn't change the fact that it's still impedance.

The NEC should be revised then.

I make a big deal out of this because we must be technically correct when having these discussions and arguments.

What makes you think the terminology is incorrect? There is no good technical reason they picked 25 Ohms that I can come up with, so why is it out of the realm of possibility that when they said resistance they meant resistance?

Just out of curiosity - does anyone know when an actual test is done is resistance or impedance actually measured? I seem to recall it is done with a battery as the source which would tend to imply it is resistance.

 

[infinity]

Back to the original question, I was talking to the UL rep on panel 5 about this, and he said that the intent is that at least one of each electrode type is to be used. I realize this is not a formal interpretation, however. He also stated that they are hoping to clear this up for the 2008 cycle.

I think that I said this back on page 1:

The requirement is to use all of the available types of electrodes. The type of electrode is described in 250.52(A)(1)-(6).

I do hope that they clear this up in the 2008.