bonding metal street light poles

[peter d]

Re: bonding metal street light poles

Originally posted by TOMWELDS:
In regards to a neutral being neutral (L), If 2 wires come off a transformers secondary, what made the neutral a neutral? The fact that one of the wire's was grounded. Otherwise it's just another hot wire (like 240volts).

Im still studying the animation. It seems there's more to the picture than first glance. Imediatly im thinking what would happen to that fellow if there was NO ground rod. Also, picture the same scenario with a house electrical system.

First of all, if one of the conductors is intentionally connected to earth, it becomes a grounded conductor. A true neutral is only present in very specific situations. A common 120 volt system with a hot and grounded conductor does not contain a "neutral."

The person would be safer without the ground rod because the earth he is standing on would not be live. He would still receive a dangerous shock or be killed if he touched the pole and had a good path to a grounded surface via his body. The ground rod without a low impedance path back to the source elevates the touch potential as shown in the illustration.

 

[pierre]

Re: bonding metal street light poles

Tom
it might behove you to take about an hour or two and spend some time on this site in the "other" portion (on top of the page) - click on it and click on newsletters. Read Mike's grounding and bonding posts, there are many of them, some including his very good graphics. This should help with your understanding of how grounding and bonding differ, a maybe help a little with the theory end of it.
In reading your posts, I see that your understanding of this topic needs some updating.

 

[roger]

Re: bonding metal street light poles

Originally posted by TOMWELDS:
In regards to a neutral being neutral (L), If 2 wires come off a transformers secondary, what made the neutral a neutral? The fact that one of the wire's was grounded. Otherwise it's just another hot wire (like 240volts).

Not true, although we are required to ground it, the X0 connection can be a neutral with out grounding it.

Roger

 

[TOMWELDS]

Re: bonding metal street light poles

Roger, good diagram....my point was 'what made the neutral safe. My bad grammer..LOL. Regardless of the load, its dangerous to earth until grounded..unless its at 'zero'.

With regards to the post..that's all fine, but in reality, the post is mounted with steel 'J' bolts which will have the same effect. So if true, the same problem will always exist.

 

[peter d]

Re: bonding metal street light poles

Tom,

The bottom line is that the pole MUST have a low impedance connection back to the SOURCE, not the ground.

Now, what utilities do is another manner entirely but under the NEC, such as parking lot lighting, the installation must include an grounding conductor, which in reality is a bonding conductor.

 

[TOMWELDS]

Re: bonding metal street light poles

I was just talking in reality...not in a perfect world.

 

[tom baker]

Re: bonding metal street light poles

" If the pole is connected to a ground rod, in the event of a ground fault, the path will go to earth and not thru the dog's chain leash or person leaning on the pole."
No, never. The electrons do not want to go to earth, they want and have to go back to there source, the transfomer.
We have been taught that electricty takes the path of least resistance, which is false. If it was true, then 9 year old Victoria Quail would not of been electrocuted in Sacromento California when she touched an enegized light pole and the metal fence at the same time.
Electrons take all paths of resistance, your body has a resistance of about 1,000 ohms, in parallel with a metal lighting pole, you will have about 90 ma through your body.
Tom I understand your confusion. Much of what we have been taught about grounding is wrong.'
If it was right, then Victoria Quail would be alive today.
I have the orginal article if you would like to see it.
A low impedance fault current path is always required. A ground rod at a metal lighting pole does nothing, unless of course, it is a time and materials job. Do the math with ohms law, and you'll understand.

 

[TOMWELDS]

Re: bonding metal street light poles

Im not confused or for that matter, stubborn...lol...The picture shown is not complete. It's being viewed on assumptions. That being, the transformer feeding it is isolated, no grounded neutral. Or is it? The transformers here (on street lighting) have the neutral grounded. Also, the theory shown is valid if the pole is isolated from the earth..not practical..ie: j bolts, etc.

 

[TOMWELDS]

Re: bonding metal street light poles

And i apoligize for using the statement 'electricity wants to go to earth'. Just a habit since it's usual path back to source is thru the earth via the ground system.

 

[roger]

Re: bonding metal street light poles

TOM, look at this graphic and notice that the source and pole both have rods but there is no low impedance fault clearing path (EGC) back to the source.

You can do the math and see the 20 amp breaker will never open and the current flowing through the heart can certainly be fatal


Roger

 

[TOMWELDS]

Re: bonding metal street light poles

I understand what you're saying, but are you better off with NO ground rod? The base is not going to ever be isolated from the earth. So in one manner or another, the problem exist. So, isnt the ground rod the lesser of the evils? After this, we're left with grounding the neutral at the pole or using ground fault.

 

[roger]

Re: bonding metal street light poles

TOM the ground rod or the pole being grounded through the base bolts is not a problem IF there is an Equipment Grounding Conductor in place that will clear the fault.

The ground rod will assist in dispearsing a HV surge or Lightning event, but not in providing touch potential safety.


BTW, welcome to the forum.

Roger

 

[TOMWELDS]

Re: bonding metal street light poles

Roger, thank you for having me...

I guess my question is..what's the answer?...lol...I may seem difficult because im trying to make a good situation from a bad one.

 

[romeo]

Re: bonding metal street light poles

I thank everyone that responded to my post. I will bring you up to date on the final wiring of these metal light poles at a subdivision where I am the inspector. I was lucky in having been able to get the Executive Director Of The State Board Of Examiners Of Electricians to look at this installation, who agreed that it is a dangerous situation.

The bottom line seems to be the utility co. could use their own standards to wire these poles and the NEC did not apply,however in this state the inspector was authorized to inspect.

The problem was that the poles were not wired as per their specs. Their specs. show the grounded conductor bonded to the pole and they did not do this. Although I disagree with this method it is better than no ground at all,as they were depending on a ground rod to provide a return path to the source,and we all know that will not happen using 120volts.

The end result is I was able to get them to bond the pole to the grounded conductor and also to the ground rod as shown in their specs. I am still not convinced that this will clear a ground fault as there is no secondary overcurrent protection. They claim that a ground fault will trip the primary cutouts (WOW I WONDER IF IT WILL ) Also i pray that the grounded conductor does not ever become open.

I just wonder why with all of the engineers the utility co. has one of them doesn't see the light and start using a EGC. and provide A safe ground fault return path.

These poles are located not more than 10' from the lawns of the home owners,I worry about the children playing in a rain storm in the heat of summer and making contact with one of these poles.

Again I thank all of you for your reply I feel that I did all the my position authorized me to do ( I certainly hope i did ) I wish The NEC would cover all secondary installations and let the PCO. take care of the primary. romeo

 

[TOMWELDS]

Re: bonding metal street light poles

Excellent summary, Romeo.

 

[pierre]

Re: bonding metal street light poles

From Romeo
"I just wonder why with all of the engineers the utility co. has one of them doesn't see the light and start using a EGC. and provide A safe ground fault return path."

There is only one reason
$$$,$$$,$$$,$$$,$$$,$$$,$$$

[ December 11, 2005, 12:06 PM: Message edited by: pierre ]

 

[peter d]

Re: bonding metal street light poles

Romeo,

As you said, using a grounded "neutral" is better than nothing. After all, as has been mentioned before, all services in the US use a grounded neutral for a low-impedance path back to the transformer. If the service neutral opens, the danger is just as great as if the grounded neutral supplying a pole opens.

 

[jimwalker]

Re: bonding metal street light poles

When that neutral opens guess we can barry some kid and justify it in the money we saved on running a grounding wire. :roll:

 

[jtester]

Re: bonding metal street light poles

From Romeo
"I just wonder why with all of the engineers the utility co. has one of them doesn't see the light and start using a EGC. and provide A safe ground fault return path."

The utility neutral is their ground, so you can't beat a neutral from a grounding perspective. It is actual significantly better than an NEC EGC because it is grounded at every pole, and is usually the same size as the phase wire.

I admit that there are situations where if the neutral opens up in the first run or so on both sides of the pole, you will have a hot pole, but in general having two things go wrong at one time is unlikely. Open neutrals are very unsafe, but something utilities face the potential of at every L-N transformer they have in their system. The vast majority of single phase services in the US have this potential problem.

I would submit that a utility neutral bonded to a pole is generally a better ground path than an EGC.

Jim T

 

[don_resqcapt19]

Re: bonding metal street light poles

Jim,

It is actual significantly better than an NEC EGC because it is grounded at every pole, and is usually the same size as the phase wire.

How does the fact that the utility neutral is bonded at multiple points make it better than an EGC?
Don