Do you have a detail for an ufer ground in a new residential home. I will be bonding the new service to the rebar in the slab.

Dear,

I've read your information about Grounding Specifications for Street Lighting". Can you send to me how many type to install grounding and what is the term and condition to install grounding.

Regards, Angle

http://www.solution4u.co.cc

The wiring diagram is for TN-C ( terra neutral common ) grounding where the neutral is also nthe equipment grounding conductor. However, on end grounded 2-wire single phase and corner grounded 3-phase systems the "neutral" carries full load current which means that TN-C grounding creates a lot of stray current in the soil.

The advantage of 480 volts end grounded single phase is that each ballast only needs 1 line fuse. If using triplex cable for overhead systems having separate neutral and equipment grounding conductors is very easy.

One advantage of TN-C grounding is that the potential difference between the neutral and the case of the ballast is very small even when lightning strikes. It also saves on materials which was why TN-C was promoted by the War Materials Board during World War 2. TN-C branch circuits were always a bad idea and TN-C feeders were O.K. for residential applications but bad on places like dairy farms.

TN-C branch circuits are just another bad idea just like winter daylight savings time. That was tried during the 1970s with the result that my school's power bill went UP because of needing to use room lights in the morning. The school schedule had to be delayed an hour to nullify DST. This also created scheduling problems with respect that Pennsylvania at the time required the bovernment schools to provide transportation for parochial and private schools.

The more modern method is to use TN-S ( terra neutral separate ) grounding where the neutral and equipment ground are 2 different wires. However, lightning can elevate the equipment ground voltage with respect to the ballast case which means that each ballast needs a surge protective device that protects both the hot and neutral from overvoltage.

Regarding grounding for traffic signal installations, the authoritative and definitive report on this issue was published in 1986 by the Transportation Research Board" Transient Protection, Grounding and Shielding of Electronic Traffic Control Equipment". It discusses logic grounds, grounding and how to create a single point ground. If you would like a copy, go to the Mike Holt Code Forum, and send me a PM Tom Baker, Moderator.

Can I just say I don't want to be anywhere near this system unless it has a GFCI at the source? All it takes is one open neutral and we have a serious touch hazard available at each and every pole down stream from the fault. Even the fiberglass poles have a touch hazard since the mounting bolts are now bonded to the neutral conductor.

I suppose nearly every street lighting system is subject to this failure mode. Am I missing something here? Aren't we looking at energizing the pole with line potential if the neutral is compromised? I see no way we can trip overcurent protection if there is an open neutral. GFCI is the only life safety protection that would respond to this fault.

Cheers,

Fiberglass poles are notorious for the build up of static electricity. This may be a reason for grounding.

The grounding equipment conductor should only be connected to the ground rod. A lightining strike would be disappated to the earth. The ground from the feed should be seperate so there is no high voltage path to the feed source.

By connecting the equipment ground provides a multiple grounding path. Then the neutral and the grounding conductor provide return paths for the feed voltage and lightning strike.

If the neutral conductor failed, was disconnected, or was damaged the return path would go through the bonded grounding conductor.

Supplimental grounds are safer as long as they do not have a path back to the feed source.

Mike with the high resistance to earth the grounding rod is excellant lightning strike protection. If the ground rod was the only path the high earth resistance would disapate the high voltage.

480 Vs 277/480 A 480V system would be much more dangerous than a 277 V system as the voltage stress is 480 to ground rather than 277 V, dangerous in that the insulation is much more likely to break down. In the street lighting specs I work with, we don't allow THHW, but only XHHW-XLP2, as THHW will more often fail in an underground conduit system that is full of water. The voltage stress on motor windings caused a lot of failures with 480V corner grounded systems.

My suspicion on why we see ground rods at metal lighting poles is that that many power companies got there start doing street lighting, IE Puget Sound Power and Light. For many utilities, street lighting is a still big part of their core business. Utilities follow the NESC, a performance document, IE designed to be used by qualified persons. For grounding, its general and not specific as the NEC. And the utilities use an earth ground to clear a fault, but at voltages such as 12,500.

The NEC is a prescriptive document, IE, it tells you how to install grounding and bonding to be safe. (See 250.4), Prescriptive means follow the instruction, by not allowing the earth as a return path, and installing a low impedance ground fault return path.

So, a lot of the street lighting installed by utilities (at 600 v and below) should follow the prescriptive methods in the NEC, not he more vague performance methods in the NESC.

And on some traffic signal - street lighting installations, I see a lot of unsafe installations as some who are doing the work are not electricians, they may of learned the trade without formal education. Trust me on this as I work with signal techs, am a signal tech, write article for a signal magazine, and understand traffic signals, but am also a certified master electrician.

Several years ago I received a call about electrical surges at a business in Quincy, Ca. Upon investigating I found that the Ufer ground was not connected to the utility company's ground. Consequently all of the metal inside the building and all of the metal at the meter installation was hot with 207 volts. Even the building inspector missed this violation. In a gutter I found where a thinly taped stinger leg had bonded to the gutter. Upon removal of this fault and attaching the Ufer to the utility company's grounded neutral solved the problem.

I tested this theory with a field test in 2000 while living in Denver, CO. I disconnected the #6 Solid, Soft Drawn, Bare Cu wire from my single 8' ground rod and connected a #12 Solid THHN Cu from a 20 Amp breaker to the ground rod. After ensuring that all was set and with the proper safety equipment, I switched the breaker on. The breaker did not trip. I measured the current flow with an Amp Probe at 12 A. Using Ohms Law (V=IR), I calculated R = 10 ohms (120 volts = 12 amps x Resistance). A second ground rod placed in parallel would have resulted in a resistance of 0.2 ohms (120 volts = 600 amps x 0.2 ohms). A ground fault of 600 amps would have definitely resulted in the circuit breaker tripping.

Just wanted to say thanks again Mike for the information you continue providing to the electrical contractors. Semper Fi

How about adding Arc Fault Protection as a spec for public safety....

Is it possible that this is a 480 Volt Grounded system as is the case with a corner grounded delta?

Is this a NEC installation or an NESC? Columbus has its own electric utility. In the upper left diagram they mention a 2 wire grounded neutral, the same as utilities use. In that case, the neutral acts as both a neutral and ground. On a metal pole, the ground wire is bonded to the neutral and to the pole, and also to the ground rod if one is used.

I, like others who have posted believe this most likely is a utility spec with guidance being given under the NESC. I am not familiar enough with the NESC to discuss the rights or wrongs of the spec.

I do believe however, as Mike, that "betterment" in this case would be to follow at a minimum the NEC as it affords greater safety than noted in this spec. With the number of accidental deaths noted on this forum as a result of street lighting defects, the NEC seems to be the more appropriate guide. Does it cost more, most assuredly yes, but what is the price of public safety?

I am not sure who wrote this, but they are very uninformed to say the least. Companies should make sure these technical writers know what they are talking about before someone is injured or killed due to their advice.

We use supplementary grounding ( ground rods) on some of our higher light poles around state campuses most all the time. They are an excellent way to discharge a lightning strike to ground. It is critical that they are only connected to the equipment ground and metal pole,never the neutral (grounded conductor).

Power companies use the same method with their butt grounds as well as groundrods.

It reaally concerns me that we seem to be seeing more of this now than in the past.

Thanks Mike for keeping us informed. You are a true beacon in a some times dark industry.

Jim Yancey-NCDOI Engineering Code Consultant Jyancey@ncdoi.net

Mike, Several REA's in our area use a corner grounded delta system, which results in 480v to ground.

I am not sure about the utility you posted here; the utilities in my area do not run a grounding conductor between poles. They also do not follow the NEC for any of their work and are not required to so if the work is for street lighting. This is the reason for their use of ground rods and the connection to the neutral. I am not defending it, just saying the installation they make is much different then the one we make.

We maintain and install street lighting in south Louisiana. I would use the utility company neutral wire for the luminaries and ground rod for the metal pole. Is this correct?

I was a jouneyman lineman before becoming a electrician. Streetlights for us were normally 120 or 240 but,wired without a ground and only a neutral. As per utility systems. With only primary overcurrent! In the air great fine. On the ground??? Yes, there are 480 volt cans for delta that could be wired as per. Instead of a 277 can. If it din\'t blow it burnt off. Before that they used 2400v series street lights.(way before me). Is this picture safer on a fault ?yes! stray voltage on normal conditions could occure. this would create less of a ground gradient if pole became hot. Needs improving!

I totally agree with all of your comments regarding the need for a solid and effective fault current path from the fixture and a metal pole back to the source to facilitate operation of the overcurrent devices. Additionally to prevent lightning induced transients from entering the building through the equipment ground and circuit conductors, It is necessary to install a ground rod at each pole which should be effectively connected to the Fixtures equipment grounding conductor (downlead) and bonded to the pole if of metal construction. The connection of the ploes bare ground conductor to the rod should be made using an exothermic weld connection for the best results and longivity. If the pole is fiberglass then bonding of the anchor bolts to the same point of connection as the equipment grounding conductor and the bare ground aux/supplementary rod conductor would ensure they were at equal potential to earth ground.

I have had experience with several previous cases where the client had re-occuring physical damage to pole mounted fixtures and flash over damage to the parking lot lighting panel located inside the building. The lightning induced transient voltages were following the equipment grounding conductors into the building through the feeder conductors installed in PVC conduits.

The solution and corrective actions performed at each location was as follows: 1. Installing a ground rod at each pole and correcting grounding connections as described above. 2. Installing a service entrance surge arrestor rated at the correct voltage on just the poles with the home run conduits from the building. The surge arrestor was installed inside the pole hand hole. It was connected to the Home run feeder conductors, the equipment grounding conductor & rod conductor termination point inside the pole hand hole near the base. 3. Installation of a properly rated TVSS device to the inside panel serving the parking lot lights.

Thank you for the opportunity to share my comments.

Larry LeSueur CPQ,CBCP Technical Services & Commissioning Group Barrett Woodyard & Associates, Inc. Atlanta, Georgia 30092 Direct Line 678-301-2246

With regards to a ground fault and ground current returning through the earth to the source (service / transformer). The easiest way to protect against a GF on any outdoor circuit is to install a GFCI breaker. The calculation of 277V / 25 Ohm is irrelevent if the breaker is designed to pickup at 5-10 mA unbalance between the Phase and Neutral. ANY current above the 5-10mA not returning on the system neutral will cause the GFCI to trip. The intent of the ground round is to provide a path for (some) return current, but not a "path" for the entire available fault current (or even the long time pickup value of the breaker - assuming we're talking about a 20A branch circuit breaker). Anything within touch or step potential range should be bonded so as to create an equal-potential plane.

I agree with just about all Mike has presented, and we had Mike as a presenter to staff and contracted maintenance personnel when we were emphasizing proper grounding and bonding for highway lighting AND traffic signals (which also may be misunderstood by civil engineers). (Mike did a fine job). However, as I have explained to Mike, since whenever we have concrete foundations for light poles, high mast light towers or even traffic signal poles, we have a Ufer electrode that is a structural support with at least the possibility of un-seen sub-surface damage should the pole take a lightning strike. Adding a ground rod bonded to the reinforcing steel is inexpensive insurance against such damage and risk. It is a choice. By no means does this replace the low-impedance equipment grounding conductor; that equipment grounding conductor, run with the circuit conductors, is an absolute must. This approach was supported by another expert on this topic, Greg Bierals, when we were working with him on this subject and that is what we are doing at IDOT in northerastern Illinois.

I'm fairly certain that the NEC2002 codebook says that if you don't have the 25 ohms or less to install another ground rod .But, that is the only additional rod the codebook requires to be installed. If two rods don't do it , you don't need to continue to install Ground rods until you comply with the 25 ohms or less requirement .This may have changed in the 2005 codebook but , the 2002 book is the one we studied in my appenticeship classes and the one I'm most familiar with. If the Codebook has been changed to say to keep adding rods, I apologize for any confusion I may have caused. Jeff

I know of at least one parking lot lighting system served by a corner grounded 480 volt system. Why is this erroneous and dangerous thinking so persistent, and the training so pervasive?

Mike,

When you get a chance take a look at a light rail system. The overhead contact system is attached to metal poles. The metal poles are grounded to a ground rod embedded and sometimes bonded to the rebar in a drilled shaft foundation. This is a pretty good grounding (bonding) scheme with one exception. The overhead contact system is DC powered and is positive. The running rails (track) are the return path (negative) to the substation. The running rails are isolated from ground (earth) with a minimum of 500 ohms resistance to help prevent stray currents from leaving the rail and corroding underground metallic pipelines.. If the pole becomes energized from the DC + the pole just heats up and the substation relays just see a normal current draw. The pole ground are somewhat effective for lightning protection.

Actually there are "straight" 480 volt systems still in use today. Mostly used for large street lighting projects as well as in some sports lighting installations. Im not real sure of the mechanics behind this one bank system but it does in fact deliver 480 volts to ground/neutral, and standard 480 volt ballast (for lighting) work just fine on this system. Just figured I would comment on my own personal experience

This specification for grounding lighting poles was so bad it was dangerous. I find it hard to believe that a P.E. could have written this. The drawings were well done even though they were wrong, so he gets a''D'' for them. For METAL poles we always drive a ground rod but for lightning purposes. This allows for a lighting stroke on the pole to drain down to the ground rod thus minimizing the induced voltage due to the lightning hit being carried back to the branch circuit protective device on the branch circuit wiring. Another parallel path for the lightning to get to earth is the pole anchor bolts too, this could cause damage to the concrete base too. But since the most predictable thing about lightning is that it is unpredictable.... who knows?

Grounding rods vs preaching they serve no purpose. . .

Electricty does strange things in its multiple routes to ground. Every path and instance of injury or damage cannot be perfectly explained. We can make farily accurate assumptions based on our understanding of electricty, but the power is disconnected before rescue and repairs are take place.

Is is possible that a shorted ballast in the fixture might energize a rain soaked pole and a grounding rod dissapate enough of the voltage to protect life. Maybe . . . Maybe not in a perfect situation. Does having a requirement to ground a fiberglass pole create a problem?

As far as grounding helping to save equipment, the following description of events are very real and accuratly described:

On Jan 6, 2002, Okaloosa County traffic signal technicians were called to make emergency repairs to the intersection of US98 @ Beach Drive. A power line had fallen across the mast arm located on the NE corner of the intersection.

By the time signal technicians arrived, the power line had been repaired but there was extensive damage to the intersection. The poly signal assemblies were actually blown apart and completely destroyed. The intersection’s signal cabinet (which was located on the opposite side of a the six lane divided highway), electronic equipment, and wiring were badly damaged. All damage was directly caused by the power line’s contact with the mast arm, which took every available path to ground.

The signal pole that was struck recent modifications and the pole’s grounding wire was removed from the intersections grounding system (all poles are supposed to be connected to grounding rods which are all bonded with #6 wire).

The intersection was repaired and the pole was connected to the grounding system.

In a freak coincidence, the power line fell again on Feb 27, 2002 in the same spot as the downed power line of Jan 6, 2002. This time, the mast arm was grounded. Within inches of the power line's contact with the arm, new equipment had been installed that enables emergency vehicles to activate signal changes.

There was damage to the intersection, but it was much less. The signal housings and lenses were not badly damaged (Approximately 8 lamps burnt out). Newly installed emergency vehicle equipment was not damaged. The signal wiring was not burnt. The microprocessor was not damaged.

The intersection was placed back into operation within minutes after a survey of damages.

Why does having a requirement for grounding create such a problem? If an educated person of reasonably sound mind has the authority to include grounding in the specification and the installers do not follow the specification . . . fire them. If they wish to debate the spec that might be a different issue for discussion, but what is "dangerous" is simply ignoring specs.

Addition to previous comment regarding grouniding of equipment: All signal poles are connected to ground and all grounding rods are connected to each other throughout the intersection to complete the grounding system.

Addition to previous comment regarding danger of ignorring specifications: This forum is one example of many dicsussions and debates that illustrate the hugh lack of understaning of eletricity. Continuing to express (and broadcast) opinions that some specifications are a "waste" or completely unnecessary is irresponsible and that is dangerous to goals of improving safety and workmanship.

There may be many helpers and laborers with minimal knowledge of electricity for every skilled electrician. make the lives of the unskilled easier . . . make yourself look all knowledgable . . . . "That spec is a waste" . . . lets forget about the specs, wrap this up and go home. it . . . Way to go! NOT!

Hi Mike, I would like to see that diagram bigger, I can't comment on anything because I can't see any thing on the detail because it's too small to see. If you can do something that would sure be appreciative Thanks, Jerry

My only thought on grounding a fiberglass pole would be:

There may be a chance someone could be shocked during a heavy rain storm, with the entire surface wet?

Fiber glass rods are a composite and some of them have metal mixed in the fiber glass.

I have worked on 480V to ground systems plenty of times mainly with parking lot lighting. The welcome sign to the City of Miami Beach on the Julia Tuttle Causeway is also 480V to ground.

The fiberglass pole has metal conductors running up it and to the light fixtures. The ground wire is connected to the metal anchor bolts. Lightning can be attracted to all of these metal parts. The ground rod at the pole is to help dissipate that energy to the earth.

One more legend to bury. Lightning is not attracted to anything. NO, they are not attracted to lightning rods. The lightning rods are struck because they are higher than the house. All plastics will fry and burst into flames if a lightning charge is conducted through them-I don't care if they have embedded silver threads. What you are doing with a grounded rod and conductor is giving the lightning a low resistance parallel path-and this application as described by Mike seems to me to be pretty stupid for many reasons.

Bob

Took two seconds to Google "Street Light Betterment" and come up with document from Columbus, OH

There is a corner ground open delta system still in use where a and b phase is 480 to ground and c phase is zero until there is a load, where it becomes 480 to ground also. Very rare I believe, I have only seen it once.

It sure would be hard to bid on a project with these specs. I've driven 3 10ft grounds and still had 72 ohms before. better figure a couple truck loads of grounds.

As you know many street lighting systems are owned or mantained by the utility. No service disconect or meter. The utility "neutral" is the system ground and I belive the ground rod is to dispate a lighting strike. We are always replacing "blasted luminares". The attempt to connect to the anchor bolt (bad structural choice) might be a perverted attempt at a "ufer" ground since most foundations have some sort of rebar. But most likely while cause foundation damage if it takes a lightning. We often see roadway lighting specs applied to metered services and parking lot lighting.

Most utilities that provide 480V street light systems do so as single phase, 2 wire, 480V to ground. It's not a misprint.

Mike,

Many municipalities use a 480 volt to ground system on their street lighting. You can do one of two things to achieve 480 to ground. On a 3 phase system you would corner ground the secondary of the transformer (delta)

On a single phase system you would just have a 480 volt secondary and, ground one leg.

Quote from Mike Holt: "Author’s Comments: Typically, an auxiliary electrode (what the 2008 will call the supplementary electrode) serves no useful purpose."

That's a typo. It was a "supplementary", and will become an "auxiliary" grounding electrode in the 2008.

Mike, I have two answers for you: 1. 480 to ground is a typical system used in roadway illumination. We no longer install it here in Texas because of problems with maintenance, installation, and design. We now install 240/480 single phase. 2. Yes, proper electrical design, including grounding, is a problem because most transportation engineers are Civil Engineers who go into MEGO (My eyes glaze over) when anyone tries to talk electricity. I know because I'm both a Civil Engineer and a Master Electrician. Notice where I'm working now.

Mike,

This brings up another issue in which transformers are shown 480 Δ but read 277/480 on the secondary. We'll save that for another time.

A 480 Delta "corner ground" has one phase grounded. "A" to "B" = 480 volts, "A" or "B" to "C" phase/ground = 480 volts, period. Those voltages are present all the time with or without load. "C" phase to ground should equal zero volts.

Besides highway applications, this configuration is also used in hazardous locations; generally textile mills and I have seen some coal mines using it too. If a motor, for example, shorts to ground the overcurrent protection trips with no arcing.

With a three phase branch circuit feeding lights, it would be 3 wire + gnd; there should (shall) be no neutral.

Joe Pfau

One other comment regarding the auxiliary electrode; the only purpose for it would be as part of a LPS. Any adjunt bonding to an electrode creates a potential (no pun intended) hazard during a fault condition.

Joe