AHJ Grounding Electrode Requirement

[Rick Christopherson]

Edit: Sorry for the tone, but I knew someone was going to bring this up sometime today, and I was a little over-prepared for it.

Rick you might want to re-think this statement.....................

..................... since most utility's bond both the primary and secondary neutrals to an electrode at the pole..............

I sure as heck hope you're not installing systems with a primary-side center-tap jumpered to the secondary-side center-tap, because with a few exceptions, doing so will kill someone. (P.S. The NEC defines this a non-seperately-derived-system.) Even those exceptions will still have some exceptions that can still kill someone.

Why?

Because if your primary (the POCO) lost a phase, then the primary center-tap will get slammed to the high-voltage of the remaining (non-lost) primary phase voltage, and it will take the secondary center-tap with it. All of the downstream customers of this transformer will suddenly have primary-voltage on their neutral conductor. Since all of their mains are bonded, their grounding system will also be carrying primary-side voltage.

Anyone more than a couple feet away (aka the Shells mentions previously) from their grounding electrode, yet touching both an earthen-ground (aka concrete floor or grass) while also touching a grounding/grounded conductor of the dwelling's electrical system will experience near-full primary-side voltage across their body. They will be toast!

But my response is that any voltage placed upon the water pipe will not be brought down to the potential of Earth because of the resistance of the Earth in the close proximity of the water pipe, which will be to high to ever do this..............

This is why I keep bringing up Ohm's Law! It makes no difference how high the resistance, if there is no current flowing, then Ohm's Law dictates that there can be zero voltage (or more specifically, zero voltage-difference). Several of you have made this statement, but you all assumed that there was high current (aka fault current) that was not part of the discussion. Not all voltage elevations on the grounding system are the result of a direct fault.

I think for the most part we are on the same page but we must remember that the current is not trying to return to Earth, it is trying to return back to source.......

No! As I have stated many times in the past; electrons do not care where they came from or where they are going. They only care about a difference in voltage, regardless what caused that difference in voltage. When you think of electricity as only following a return to source then you loose sight of the many other aspects that control the flow of electrons.

 

[Rick Christopherson]

That and the fact it is very likely to be connected multiple times to the MGN due to the neighbors bonding.

We have had past discussions about "super nodes" through the shared plumbing system before. However, during the course of those discussions it was revealed that too many situations were attributed to this fairly rare problem. It is far more rare (problem wise) than it was being given credit for.

 

[hurk27]

I guess many on here know I have very little faith in grounding electrode systems on this side of the utility transformer, there is a good reason for this lack of faith, I spent 3 years at the University of Florida studying lightning and Earth connection (grounding) to mitigate the effects of lightning, in the many experiments we did, we found many faults in so many theory's that many hold as truths, some of which is in the NEC and sadly also in many engineering books that continue these myths that many have grown so accustom to believing.

In perspective with the OP I don't feel as much a danger as to the effect of not using the water pipe as an electrode as much as the effect of not applying the 250.104 bonding requirements and what could happen if the pipe is energized via a water heater element or other source, to me it is this bond that does far more good for safety then using the pipe as an electrode ever will.

With that said I will say that like Bob also has pointed out, that if the water pipe is a continuous low impedance path to the next service down the street then and only then will it allow some protection from a lost neutral or other type of fault.

 

[hurk27]

Edit: Sorry for the tone, but I knew someone was going to bring this up sometime today, and I was a little over-prepared for it.

I sure as heck hope you're not installing systems with a primary-side center-tap jumpered to the secondary-side center-tap, because with a few exceptions, doing so will kill someone. (P.S. The NEC defines this a non-separately-derived-system.) Even those exceptions will still have some exceptions that can still kill someone.

Why?

Because if your primary (the POCO) lost a phase, then the primary center-tap will get slammed to the high-voltage of the remaining (non-lost) primary phase voltage, and it will take the secondary center-tap with it. All of the downstream customers of this transformer will suddenly have primary-voltage on their neutral conductor. Since all of their mains are bonded, their grounding system will also be carrying primary-side voltage.

Wow, guess we have many dangerous Y primary systems in the US as every transformer I have seen had the secondary center tap bonded to the MGN???

 

[Rick Christopherson]

Wow, guess we have many dangerous Y primary systems in the US as every transformer I have seen had the secondary center tap bonded to the MGN???

Hmmm? I must have missed the part where I said there were some exceptions. I must have also missed the part where I said that even those exceptions have exceptions where they can also fail.

 

[don_resqcapt19]

Hmmm? I must have missed the part where I said there were some exceptions. I must have also missed the part where I said that even those exceptions have exceptions where they can also fail.

Some exceptions? The connection of the primary MGN to the secondary grounded conductor is done by almost all utilities in the US.

Also it is no more of a non-SDS than any transformer the electrical contractor would install. Code compliant installations of SDS transformers will always have a connection between the primary and secondary grounded conductors, assuming that there is a grounded conductor on both sides. This connection will be via the primary and secondary EGCs.

 

[Rick Christopherson]

No they are not, and you need to read up on what constitutes a seperately derived system. Bonding primary neutral (or center-tap) to secondary neutral automatically constitutes a non-seperately-derived-system.

 

[hurk27]

Edit: Sorry for the tone, but I knew someone was going to bring this up sometime today, and I was a little over-prepared for it.

I sure as heck hope you're not installing systems with a primary-side center-tap jumpered to the secondary-side center-tap, because with a few exceptions, doing so will kill someone. (P.S. The NEC defines this a non-seperately-derived-system.) Even those exceptions will still have some exceptions that can still kill someone.

Hmmm? I must have missed the part where I said there were some exceptions. I must have also missed the part where I said that even those exceptions have exceptions where they can also fail.

Rick the statement you made was in direct response to my statement of a normal way POCOs wire all Y fed transformers, The neutral of that bank might not be bonded on the primary side but it is very common that it is where you have a single tank and is very common with a 3 tank Y feed, now we don't bond the X0 on a common core transformers, but that is a whole nother discussion, so where are you even leading this or are you just feeding the pot??

don't twist things around like this then come back and act like your saying something else its too obvious

 

[don_resqcapt19]

...
This is why I keep bringing up Ohm's Law! It makes no difference how high the resistance, if there is no current flowing, then Ohm's Law dictates that there can be zero voltage (or more specifically, zero voltage-difference). Several of you have made this statement, but you all assumed that there was high current (aka fault current) that was not part of the discussion. Not all voltage elevations on the grounding system are the result of a direct fault. ...

The most common source of voltage on the water pipe is the voltage drop on the primary and secondary grounded conductors. The parallel path via the water pipe and the earth does provide a small reduction in the voltage drop but not very much. There is no way to make this voltage go away.

 

[Rick Christopherson]

Rick the statement you made was in direct response to my statement of a normal way POCOs wire all Y fed transformers, The neutral of that bank might not be bonded on the primary side but it is very common that it is where you have a single tank and is very common with a 3 tank Y feed, now we don't bond the X0 on a common core transformers, but that is a whole nother discussion, so where are you even leading this or are you just feeding the pot??

don't twist things around like this then come back and act like your saying something else its too obvious

First off, your original posting made no mention of a Y-Y transformer, which is in fact one of the primary exceptions I referred to because it contains a physical neutral conductor connected to the center-tap of the primary. Outside of a Y-Y transformer, there are very few exceptions that do not pose serious danger. Even the Y-Y is not danger-proof, but it does require loss of both the primary neutral and one or more primary phases.

However, since the OP is discussing residential service, a Y-Y transformer is not even in the equation.

So if you are going to refute what I stated, then refute it within the context of the discussion and limit your comments to a single-phase secondary (regardless of the phase of the primary).

 

[hurk27]

First off, your original posting made no mention of a Y-Y transformer, which is in fact one of the primary exceptions I referred to because it contains a physical neutral conductor connected to the center-tap of the primary. Outside of a Y-Y transformer, there are very few exceptions that do not pose serious danger. Even the Y-Y is not danger-proof, but it does require loss of both the primary neutral and one or more primary phases.).

And where prior to your post 41 was it ever mention of a Y-Y transformer only after that post was it mention

However, since the OP is discussing residential service, a Y-Y transformer is not even in the equation.

So if you are going to refute what I stated, then refute it within the context of the discussion and limit your comments to a single-phase secondary (regardless of the phase of the primary).

Again prior to your post 41 we were discussing a single phase system were we not? and if I mention a primary neutral would you not think I was talking about a Y primary system? does a delta system have a MGN, yes in some cases using zig-zag transformers, but I would not see the danger you brought up with the secondary neutral tied to a zig-zag derived MGN either??? in our area deltas are not used for local MV primary feeds only HV sub-station feeds so maybe it was mis leading on both our parts but not sure how?:?

 

[hurk27]

You know Rick, I would have never assumed that when someone mentioned of bonding between the primary neutral and the secondary neutral they were even thinking of a bond to a un connected center tap on a delta feed tank (line line fed) that would have never entered my mind:?

 

[Rick Christopherson]

Edit: This posting was made before reading your last posting. I am still digesting what you mean with that posting.

And where prior to your post 41 was it ever mention of a Y-Y transformer only after that post was it mention

I didn't mention Y-Y, you did, or at least directly implied it with the implication of a primary-side neutral. You certainly won't find a primary-side (POCO) center-tapped neutral on either single-phase or delta, so that only leaves Y-Y.

 

[hurk27]

Edit: This posting was made before reading your last posting. I am still digesting what you mean with that posting.

I didn't mention Y-Y, you did, or at least directly implied it with the implication of a primary-side neutral. You certainly won't find a primary-side (POCO) center-tapped neutral on either single-phase or delta, so that only leaves Y-Y.

And my point exactly, since my comment was to a primary neutral connection your comment in post 41 made no sense which is why we are having this conversation:happyyes: as if you saw that I was talking about a single bushing primary tank you should have known it was a Y fed system that I was talking about and the comment in post 41 was un-necessary and confused me all the heck:blink:

 

[Rick Christopherson]

Ignore the electrical jargon. How many wires are on the primary side of the transformers you speak of?

 

[hurk27]

Edit: This posting was made before reading your last posting. I am still digesting what you mean with that posting.

I didn't mention Y-Y, you did, or at least directly implied it with the implication of a primary-side neutral. You certainly won't find a primary-side (POCO) center-tapped neutral on either single-phase or delta, so that only leaves Y-Y.

just saw the above in red:
are you saying you will never have a Y system feeding a single phase tank with one bushing? I beg to differ, as that is the way it is around here, a single bushing tank with a common tank bond for the MGN and the neutral running to the house

 

[hurk27]

Ignore the electrical jargon. How many wires are on the primary side of the transformers you speak of?

one phase conductor and the MGN to the tank, common with the neutral to the house, the tank has internal bonds to the case.

 

[hurk27]

I should add that our local fed system is a 12.47/7.2kv system

 

[Rick Christopherson]

one phase conductor and the MGN to the tank, common with the neutral to the house, the tank has internal bonds to the case.

That's what I thought. Now go back and re-read all of my postings on this topic. I have (within the best of my abilty) tried to not confuse the jargon of "neutral" with center-tap.

 

[hurk27]

That's what I thought. Now go back and re-read all of my postings on this topic. I have (within the best of my ability) tried to not confuse the jargon of "neutral" with center-tap.

Well true and I forget that not everyone is on a Y system as many are on delta local sub feeds, I need to remember this, but in my area our MGN is a Y and I think Don is also as to why his response, but even with a delta system you will still have a MGN using a ziz-zag tie which should not cause a problem being bonded to the secondary neutral to the dwelling.

It is easy to get lost in the slangs each areas might use.