another electricution - metal street pole-baltimore!

[charlie tuna]

Re: another electricution - metal street pole-baltimore!

just like thirty years ago --- our industry knew there was a problem with outside receptacles--too many people were getting killed on them. there came the invention of the gfi and it was instituted into the code with limited required locations. now, we are seeing these areas extended because they save lives. another item is arc fault protection devices---instituted via the nec. when we as an industry, realize there is a problem with improper bonding of metallic utility poles (etc) and that the supplemental ground rod only increases the risk of miswriting the pole- while not providing any other function--we should discontinue this practice?

 

[charlie]

Re: another electricution - metal street pole-baltimore!

Charlie Tuna, while I understand your concern, the answer is education, not restricting additional grounding. There have been comments about a built in Ufer ground in the base of street light columns but that is not quite true. Take a look at the requirements for a Ufer and then at the surface area at the bottom of a column foundation. You will notice that the "Ufer" in the foundation doesn't quite make it. Additionally, what type of rule are you going to write for the direct imbedded fiberglass columns?

There are electricians and engineers who do not know how to properly bond and ground equipment. The problem, as I see it, is to get to those people and educate them. Generally, it is those people who are not interested in boring stuff like grounding classes.

 

[petersonra]

Re: another electricution - metal street pole-baltimore!

My point about a "built in" Ufer was not that the pole base met the requirements for a concrete encased electrode, but that what was there might well be a better grounding electrode than a driven rod. I think I even said it that way.

 

[charlie]

Re: another electricution - metal street pole-baltimore!

Bob, you are not the only one to say that but (I think) you are the only one to say it in this thread. You were correct in the way it was framed but there are a lot of people that believe the Ufer in the foundation is much better than a ground rod. I do not believe any testing has been done for anyone to make a definite statement one way or the other.

The bottom line is that we are on the same page (I think).

 

[physis]

Re: another electricution - metal street pole-baltimore!

I've been thinking that too. It's metal bolted to the sidewalk. If that is'nt grounded then the whole idea of what grounded is is just getting too slippery to grasp. I understand you might want a better ground, but still. should we wrap the whole planet in steel mesh or is that going too far?

 

[don_resqcapt19]

Re: another electricution - metal street pole-baltimore!

It's metal bolted to the sidewalk. If that is'nt grounded then the whole idea of what grounded is is just getting too slippery to grasp.

That is the problem with using the words "grounded" and "grounding" when talking about the fault clearing path. We don't make these things safe by grounding, we make them safe by bonding.
Don

 

[physis]

Re: another electricution - metal street pole-baltimore!

That's true Don. But isn't it really "neutraling"? Unless you don't have one of those.

Edit: I agree with you though, a lot of confusion and misunderstanding is generated there.

[ December 29, 2004, 01:24 PM: Message edited by: physis ]

 

[charlie]

Re: another electricution - metal street pole-baltimore!

Maybe this will help a bit. Imagine a completely isolated system that is not connected to the earth. You install the bonding conductors (grounding conductors) throughout the system with every circuit and feeder. The neutrals (grounded conductors) are floating all the way back to the service equipment. At the service equipment, the bonding conductors meet up with the neutrals and get aquatinted since they have not met before. A short wire connects them together (the main bonding jumper) and only the neutral goes back to the electric utility transformer. The system will work perfectly and even carry fault current but there is nothing to carry static away, protect us from higher voltage to ground, or the effects of lightning.

Everything works and nothing is connected to the earth, even at the electric utility transformer. Now (and not before), take the step of earthing the system because it is not connected to mother earth. First, the electric utility will connect their transformer and the secondary common point to the system neutral. Next, a grounding electrode will be installed and connected to the same point. This has nothing to do with fault current since that has already been addressed.

Now it is the customer's turn to connect to the grounding electrodes. These connections will be made from the service equipment to Ufer grounds, building steel, water piping, ground rods, ground rings, etc. Again, this has nothing to do with fault current since that has already been addressed.

Now the customer wants to place some additional grounding electrodes in the parking lot. That is fine if he wants to attach them to the bonding conductors since the neutral is supposed to float. Again, this has nothing to do with fault current since that has already been addressed.

I have a feeling that I have just insulted the intelligence of every person in the forum. I hope, however, that I have made it a little more clear for just one. Sam, I am not pointing a finger at you but your comment gave me the idea for writing it, thanks.

 

[physis]

Re: another electricution - metal street pole-baltimore!

You mean that was my fault?

 

[charlie]

Re: another electricution - metal street pole-baltimore!

 

[friebel]

Re: another electricution - metal street pole-baltimore!

This thread is really getting to be a long one, but it shows that people are interested in Safety and saving lives when it comes to the light poles in shopping centers, etc.
Now, someone mentioned a Ufer ground, instead of a driven ground rod.
The 2002 NEC does not mention the Ufer grounding system by name, but it can be found in Section 250.52(A)(3)Concrete-Encased Electrodes.
We have used this system extensively in industry, because it has been proven that it is better than a driven ground rod.
Again, I am going to repeat what I said many threads back, that the only and best way to ensure that we have a good ground on our light poles is to carry the EGC that is properly fastened to the light pole, and to take it back to the electrical source that feeds the light. The only reason for the driven ground rod or the concrete encased electrode is for LIGHTNING and high voltage surges.
I have attended Mike Holt's seminar on Grounding & Bonding, and I have purchased his tapes and use them in teaching Grounding & Bonding. But believe me, I could watch these tapes over and over again and I will admit that I do learn something each time. If you ever get the opportunity to attend one of Mike's seminars on Grounding & Bonding, do yourself a favor and attend one. I know that I would if he comes back into my area again.

 

[apauling]

Re: another electricution - metal street pole-baltimore!

Charlie: a polite question (I misread you before): you said that where the isolated system is all connected to itself, before any connection to earth by utility or user that there existed two conditions, one was that there was a potential between the system and ground. could you explain how this potential exists?

paul

 

[charlie]

Re: another electricution - metal street pole-baltimore!

Paul, I don't follow your question. Where did I say that a potential exists between the floating system and earth? The only way there would be potential would be static, lightning, or contact with a higher voltage to ground. The latter could be a higher voltage overhead line falling into the secondary or a primary coil failure. The reason I mention the latter is the possibility of a coil failure inside a plant on a separately derived system.

 

[physis]

Re: another electricution - metal street pole-baltimore!

One of the things that the grounding electrode does is attempts to force the earth to the same potential as neutral. They don't always match. (I personally would never expect them to match).

 

[hurk27]

Re: another electricution - metal street pole-baltimore!

By Charlie(59) I don't have a problem with that if they would have grounded the columns to the system neutral the way we do.

If this is done where a pedestrian could not come into contact with the neutral bonded parts of the pole or where the neutral is not carrying any load current in which it would be just a bonding conductor, I would not see a problem with doing this. But if the neutral is current carrying i do see a potential for a shock hazard if it's connection to the system neutral degrades or lost or even if there is a voltage drop and a pedestrian is touching the pole when all the fixtures turned on the inrush current could present a shock hazard?

 

[iwire]

Re: another electricution - metal street pole-baltimore!

Originally posted by friebel:
Again, I am going to repeat what I said many threads back, that the only and best way to ensure that we have a good ground on our light poles is to carry the EGC that is properly fastened to the light pole, and to take it back to the electrical source that feeds the light.

And again I will point out that is your opinion and not an NEC requirement.

The NEC allows many ways to ground a metal light pole.

We could run a EGC conductor, use a metal raceway or even use the neutral to ground the pole just like the power co.


250.32(A)

250.32(A)Exception

250.32(B)(2).

 

[iwire]

Re: another electricution - metal street pole-baltimore!

Originally posted by hurk27:
But if the neutral is current carrying i do see a potential for a shock hazard if it's connection to the system neutral degrades or lost or even if there is a voltage drop and a pedestrian is touching the pole when all the fixtures turned on the inrush current could present a shock hazard?

Wayne good idea or not I believe the NEC allows us to use the grounded conductor for grounding a pole.

250.32(B)(2) is not limited to feeders.

Bob

 

[apauling]

Re: another electricution - metal street pole-baltimore!

got back late. Charlie: at the end of your first paragraph, post just above my question..."high voltage to ground", which is a difference of potential. I didn't think you meant to say that that potential existed at that time. just checking.

paul

 

[charlie]

Re: another electricution - metal street pole-baltimore!

Wayne, if the multi-grounded system neutral is used for grounding other structures, it should be re-grounded every chance you get. As far as damage or deterioration of the MGN, you would have the same problem with the bonding conductor except you would not know that you had a problem.

 

[charlie]

Re: another electricution - metal street pole-baltimore!

Paul, I now understand what you were asking. The primary distribution voltage is normally a grounded wye system. In the event of a failure of the primary coil (normally the insulation) that would allow the primary voltage to be impressed on the secondary, there would be a difference in potential from the isolated and ungrounded system and the earth. This would indeed be deadly.

In addition to that, there is the possibility of dangerous static charges being impressed on the ungrounded system. Again, a difference in potential from the system to the earth.

Remember, in the above scenario, the bonding system is not connected to the building but it is still floating until later.