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Hypothetical Light pole.

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bennie

Esteemed Member
Scenario:

40 foot aluminum pole, base set in pre--cast concrete. Concrete is cured and dry. Resistance is high. Aluminum oxide essentially insulates the pole from the concrete.

Supply is 2400 volts, series primary to individual transformers. No equipment ground wire, ground fault detected by residual current relay for detecting a ground fault.

Without a driven 5/8" by 10' foot rod at each pole, the residual fault detector will not function.

Pole will elevate to 2400 volts through capacitance coupling.

There is many reasons for grounding light poles, refer to ANSI/IES RP8, ANSI C-2,

When the NESC can show that a rod is necessary for safety, how come it is not safe under the NEC?

I think it is time to crack the old engineering b00ks.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: Hypothetical Light pole.

Bennie I think the light poles most of us are talking about are nothing like your example.

Typical light pole I deal with and I think the rest of us too.

480 volt or less supply, including an EGC.

Please explain what a ground rod will do for a light pole like that.

I think you are mixing codes in your example.

What you describe would not be NEC complaint in the first place.
 
B

bennie

Esteemed Member
Re: Hypothetical Light pole.

You are correct Bob, except I am mixing good engineering with mostly non-engineering consensus code.

A ground fault, and sometimes a line to line fault, on a grounded light pole, will burn clear before tripping an internal logic breaker.

A residual current detector will dump the system.

I often talk about what could be instead of what is, is. :p :p
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Hypothetical Light pole.

Bennie,
When the NESC can show that a rod is necessary for safety, how come it is not safe under the NEC?
Click to expand...
The NEC would not permit the installation in your example because it is using the earth as the sole ground fault path. The NEC requires an EGC.
Don

[ May 06, 2004, 08:41 AM: Message edited by: don_resqcapt19 ]
 
B

bennie

Esteemed Member
Re: Hypothetical Light pole.

Don: Thanks for your input. I'm not referring to line voltage power,or human generated power.

My example is for static charges that can remain on a conductive surface long after Lake Mead is empty at Hoover Dam.

Low voltages do not leave a very high residual potential when shut down. High voltage leaves a lethal voltage after the cut outs have blown.

Everyone is focused on active lines under load. What happens when the conductive material remains charged after a power outage, as a result of capacitance coupling?

I once had a fatality on an electrostatic precipatator,(dust collector) when it was shut down for cleaning, this was at Kaiser Steel Mill in Fontana,California 1964. I was the only one trained for a safe shut down. The worker did not ground the line conductors to short out the collector grids.

He bonded(shorted) the collector grids, with is body, like a bug zapper, 75 KV, DC, at 250ma capacity. The dead line set him on fire.

My point is; A dead line or material is like a rifle, unless unloaded it is still lethal even if trigger (switch) is off.

Everyone focuses on ground fault clearing events. That is only the result of a malfunction, not the problem. The work starts later after the smoke clears.

Earth grounding is very important to bleed any residual charge from a shut down system whether under NEC, NESC, or Bennie's Code :eek: :eek:

[ May 06, 2004, 10:53 AM: Message edited by: bennie ]
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Hypothetical Light pole.

Bennie,
Earth grounding is very important to bleed any residual charge from a shut down system whether under NEC, NESC, or Bennie's Code
Click to expand...
But the IEEE Green Book says that 1,000,000 ohms is a low enough impedance to control static. I would expect that the pole installed on a concrete base would have an impedance much less than a meg.
Why would a ground rod at the pole be a better "bleeder" than an EGC ran with the power circuit? In many cases the impedance to the earth will be much lower via the EGC, than via a single rod at the pole.
Don
 
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bphgravity

Senior Member
Location
Florida
Re: Hypothetical Light pole.

I spent roughly 60-hours this past summer at the IEEE reserch center at Rutgers University in New Jersey. What I learned is that there is quite radical contradictions in theory and application of grounding systems, even among IEEE publications. There is positively no absolute correct solution known at this time.

Another thing that I learned is that "static" is not proper terminology and isn't being used anymore in the scientific community. The more proper term would be "uncancelled charge separation." There is nothing static or stationary when refering to "static electricity." There is no buildup of electric charge in a insulated object, just an imbalance of charges that have no reason or function to go to Earth.

Lightning is even a bigger mystery. There is documented evidence that there is nothing that can prevent, dillute, or redirect the surging effects of lightning. There are cases at point where one structure was fitted with air terminals, extensive grounding, and significant insulation. A neighboring structure was fitted with no protection apparatus at all. Lightning struct the unprotected structure leaving no damage and some how disrupted and damaged equipment in the protected structure. Its a game of chance. :eek:
 
B

bennie

Esteemed Member
Re: Hypothetical Light pole.

Does everyone believe that the concrete base, for a lamp pole, set 5 feet in dry silica, sandstone, and clay terrain, with a water table at ten feet is a good earth connection?

Do you believe that a lamp pole can build a static charge? In relation to the earth or any other conductive or non-conductive material?

If these answers are no, then delete this post also, it is getting out of hand.

Bennie
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: Hypothetical Light pole.

Originally posted by bennie:
Does everyone believe that the concrete base, for a lamp pole, set 5 feet in dry silica, sandstone, and clay terrain, with a water table at ten feet is a good earth connection?
Click to expand...
No it does not sound like a good earth connection, and driving a ground rod right beside that base will not make it any better.

Luckily I will have my NEC required equipment grounding conductor secured to the pole and eventually connected to earth.

Do you believe that a lamp pole can build a static charge? In relation to the earth or any other conductive or non-conductive material?
Click to expand...
No I do not, even under the worst soil conditions the concrete base will drain the uncanceled charge separation ;) and so will my EGC.

I do not think that makes me out of hand. ;)
 
ryan_618

ryan_618

Senior Member
Location
Salt Lake City, Utah
Re: Hypothetical Light pole.

Hi Bennie. As you are well aware, I'm not an engineer, and I'm really not that sharp on theory. Let me throw something out here though.

The NEC requires an EGC, which ultimatley goes to the dirt. Let us assume that the ground rod you desire gives us a resistance 25 Ohms, fair enough? Let us also assume that the grounding electrode system of the building has a total resistance of say, 20 Ohms. If I run 500' of #8 to the pole for my EGC, that will give me an additional resistance of 0.38 Ohms. 20 Ohms+.38 Ohms is still signifigantly lower than the 25 Ohm driven rod at the pole base.

Again, I'm not a theory guy, so correct me if calculations are irrelevent.
 
dereckbc

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: Hypothetical Light pole.

Ryan, what frequency are you referring too? If you are talking about static or power frequencies returning to the source or earth, then the EGC is sufficiently low impedance. On the other hand if you are talking about high frequencies, say above 1 Mhz, trying to find earth, that is another story.
 
ryan_618

ryan_618

Senior Member
Location
Salt Lake City, Utah
Re: Hypothetical Light pole.

Hi Dereck. I was referring to fundamental frequency of 60 Hz. Please, pardon my ignorance, but regardless of frequency, the exisiting grounding electrode system of the structure+the impedance of the EGC would still be lower impedance than a driven rod, right?
 
B

bennie

Esteemed Member
Re: Hypothetical Light pole.

I have driven 20 feet of rod to reach the low water table, for grounding.

My daughter has recently bought a shopping center. I'm insulating all the light poles up to about 7 feet above finish grade. I am using a spray on PVC material.

I could not get the farthermost poles to trip on a ground fault. They tripped on a 480 short but not on 277 ground fault.

I may install a residual ground detector to at least record a warning.

Now don't tell me a responsible engineer will not design safety into the outdoor poles.

Stating that a rod beside a light pole into the water table is a waste, is highly irresponsible.

If this post is against some ones religion, then dump it.

No kid is going to get killed on my daughters property.
 
P

pierre

Senior Member
Location
Westchester County, New York
Re: Hypothetical Light pole.

Bennie
The light poles at your daughter's shopping center are required to have an EGC installed and should open the OCPD with the 277 ground fault. If they are not, there are other problems you should spend your time and her money on to make sure the problem does not become worse.

I hope you are insulating the grounding electrode conductor and the grounding electrode as well - if there is a ground fault and the OCPD does not open, the metal continuity with the GEC to the grounding electrode will cause them and the earth around the pole to become energized.

Pierre

[ May 09, 2004, 11:16 PM: Message edited by: pierre ]
 
B

bennie

Esteemed Member
Re: Hypothetical Light pole.

Pierre: The poles are not required to have an equipment ground wire. There was once metal conduit.

I am going to permanently insulate the poles,even if it takes a barricade to keep anyone from touching them.

In addition I will have rods driven at each pole for residual ground current detection.

Digging up the underground conduit is not cost effective of permanent, it may work or may not. I don't like the odds.

Equipment ground conductor for what? I won't stake my life on it.
 
P

pierre

Senior Member
Location
Westchester County, New York
Re: Hypothetical Light pole.

Bennie
Try 410.18(A), 410.20, and 410.21 :)
Were not asking you to stake your life, just conform to the minimum code.

Pierre

[ May 09, 2004, 11:47 PM: Message edited by: pierre ]
 
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