I am trying to find out what method is used to bond metal street light poles using the NESC rather then the NEC. Can anyone tell me how rule 215.C1 of the NESC reads? The utility co. is bonding metal light poles to the neutral of a 110V circuit at the hand hole of the pole,and are not using a egc.Thanks for any help in advance
bonding metal street light poles
- Thread starter romeo
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- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: bonding metal street light poles
I don't have the NESC available. I know that utilities are not subject to the NEC, but I don't know if they are subject to the NESC.
The bonding point between neutral and ground has to happen at the first disconnecting means from the utility service. Would I be right in surmising that the handhole at each light pole houses the service disconnecting means for each light? If so, then that is the correct point to bond the lamp post. But if there is a common service point for more than one light pole, and if feeders or branch circuits are run from handhole to handhole, then I think you have a problem.
I don't have the NESC available. I know that utilities are not subject to the NEC, but I don't know if they are subject to the NESC.
The bonding point between neutral and ground has to happen at the first disconnecting means from the utility service. Would I be right in surmising that the handhole at each light pole houses the service disconnecting means for each light? If so, then that is the correct point to bond the lamp post. But if there is a common service point for more than one light pole, and if feeders or branch circuits are run from handhole to handhole, then I think you have a problem.
Re: bonding metal street light poles
Thanks for the reply Charlie. The branch circuit is connected to the secondary hand hole w/out overcurrent protection.The poles are owned by the utility co. I am told that they fallow the NESC. They depend on a ground rod to trip the transformer primary fuses.
Thanks for the reply Charlie. The branch circuit is connected to the secondary hand hole w/out overcurrent protection.The poles are owned by the utility co. I am told that they fallow the NESC. They depend on a ground rod to trip the transformer primary fuses.
Re: bonding metal street light poles
Where are the branch circuit overcurrent devices? There needs to be a effective ground-fault current path that does not rely on the earth as a conductor. See 250.2 I know the power company relies on the NESC, but when they are not installing generating and transmission equipment they must follow the NEC per article 90.2. It sounds like the way they are doing it may end up with energized poles in the event of a fault.
Where are the branch circuit overcurrent devices? There needs to be a effective ground-fault current path that does not rely on the earth as a conductor. See 250.2 I know the power company relies on the NESC, but when they are not installing generating and transmission equipment they must follow the NEC per article 90.2. It sounds like the way they are doing it may end up with energized poles in the event of a fault.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: bonding metal street light poles
This is in contrast to a 120 volt residential system. A ground fault that has to pass through a ground rod with a resistance even as low as 25 ohms would have a fault current no more than 5 amps, and this would not trip a 15 amp breaker.
But I think the "effective ground path on the secondary side does not rely on the earth. A fault from the hot side to the pole, let us say within the light fixture at the top of the pole, would send current down the pole, via the bonding wire to the neutral within the handhole, and immediately thereafter back to the source. That is a low-resistance path, and the resulting high current would blow the fuses on the primary side. So long as there is a transformer at each pole, and there is no feeder or branch circuit from handhole to handhole, I think it is correct to bond at each handhole.
(Edited to correct a typo.}
[ November 28, 2005, 03:52 PM: Message edited by: charlie b ]
The transformer's primary protection is not governed by the NEC, and it may rely on the earth as a conductor. But that is because at the higher voltages associated with transmission and distribution systems, the resistance of the interface between a ground rod (or the base of the pole, perhaps) and planet Earth is not too high to prevent blowing the primary fuses. For example, if the primary side is 12,470 volts (not an uncommon rating), and if the ground rod resistance is 200 ohms, then a fault would have a current of 62 amps, and this would trip a primary fuse that is probably 10 amps or smaller.
This is in contrast to a 120 volt residential system. A ground fault that has to pass through a ground rod with a resistance even as low as 25 ohms would have a fault current no more than 5 amps, and this would not trip a 15 amp breaker.
But I think the "effective ground path on the secondary side does not rely on the earth. A fault from the hot side to the pole, let us say within the light fixture at the top of the pole, would send current down the pole, via the bonding wire to the neutral within the handhole, and immediately thereafter back to the source. That is a low-resistance path, and the resulting high current would blow the fuses on the primary side. So long as there is a transformer at each pole, and there is no feeder or branch circuit from handhole to handhole, I think it is correct to bond at each handhole.
(Edited to correct a typo.}
[ November 28, 2005, 03:52 PM: Message edited by: charlie b ]
- Location
- Illinois
- Occupation
- retired electrician
Re: bonding metal street light poles
Forget everything that you know about grounding and bonding...it does not apply to the utilities. They do not use EGCs and in most cases do not ground or bond metal light poles. There is no fault clearing path.
Don
Forget everything that you know about grounding and bonding...it does not apply to the utilities. They do not use EGCs and in most cases do not ground or bond metal light poles. There is no fault clearing path.
Don
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: bonding metal street light poles
I think romeo has a worthwile reference. NESC 215.C.1 says
A good questions is what is effective grounding? It could be safe touch potential distances, because it almost certainly does not mean adequate overcurrent protection and grounding to operate those devices.
Regardless of the NEC being inapplicable, there are still requirements for grounding and overcurrent protection specified in the NESC.
Jim T
I think romeo has a worthwile reference. NESC 215.C.1 says
It clearly requires some type of grounding on metal street light poles.
A good questions is what is effective grounding? It could be safe touch potential distances, because it almost certainly does not mean adequate overcurrent protection and grounding to operate those devices.
Regardless of the NEC being inapplicable, there are still requirements for grounding and overcurrent protection specified in the NESC.
Jim T
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: bonding metal street light poles
it says "effectively grounded", not "effectively bonded".
a ground rod effectively grounds it.
it says "effectively grounded", not "effectively bonded".
a ground rod effectively grounds it.
Re: bonding metal street light poles
Thank you Bob and Jim T for your response.I would like to know the definition of grounding regarding the NESC. I guess that bonding the neutral is ok by NESC is ok but a horror show by NEC should the neutral become open any where after the main sourse. Thanks for you help and interest
Thank you Bob and Jim T for your response.I would like to know the definition of grounding regarding the NESC. I guess that bonding the neutral is ok by NESC is ok but a horror show by NEC should the neutral become open any where after the main sourse. Thanks for you help and interest
- Location
- Illinois
- Occupation
- retired electrician
Re: bonding metal street light poles
Jim,
Don
Jim,
A ground rod does not create "safe touch potential". If you are touching the pole and standing on the earth 6" away from the grounding electrode, you would be subjected to ~52% of the line to neutral voltage.
Don
- Location
- Massachusetts
Re: bonding metal street light poles
The NEC allows the equipment on the supply side of the service disconnect to be bonded to the neutral.
If the utility neutral opens and you touch the meter socket on the outside of the house in most cases you will get blasted.
Personally I would much rather the utility bonded the metal pole to the neutral than simply connecting it to a ground rod.
Same problem at every service in America.
The NEC allows the equipment on the supply side of the service disconnect to be bonded to the neutral.
If the utility neutral opens and you touch the meter socket on the outside of the house in most cases you will get blasted.
Personally I would much rather the utility bonded the metal pole to the neutral than simply connecting it to a ground rod.
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: bonding metal street light poles
romeo
Metal light poles that I am familiar with have 4 anchor bolts, usually 1" in diameter, 3' or longer installed in the base. The bolts provide 2.4 times the surface area of a 5/8"X8' ground rod. I think the comparison to a single ground rod may be in error many times.
I am not defending the practice of unsafe grounding, I am wondering how utilities can support this type of design when the NESC is very clear about grounding. The only logical explanation I can come up with is that utilities believe that touch potentials are within permissile limits.
Jim T
romeo
The NESC defines effectively grounded as Intentionally connected to earth through a ground connection or connection of sufficiently low impedance as having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazard to connected equipment or to persons.
Metal light poles that I am familiar with have 4 anchor bolts, usually 1" in diameter, 3' or longer installed in the base. The bolts provide 2.4 times the surface area of a 5/8"X8' ground rod. I think the comparison to a single ground rod may be in error many times.
I am not defending the practice of unsafe grounding, I am wondering how utilities can support this type of design when the NESC is very clear about grounding. The only logical explanation I can come up with is that utilities believe that touch potentials are within permissile limits.
Jim T
peter d
Senior Member
- Location
- New England
Re: bonding metal street light poles
This is slightly off topic but related.
I know that in Boston and probably many other parts of the country, many of the older utility controlled street lights use a direct-buried concentric-neutral cable that is simply a bare neutral wrapped around the live conductor. I am not sure of the conductor type but I think the bare wrap is lead.
This is slightly off topic but related.
I know that in Boston and probably many other parts of the country, many of the older utility controlled street lights use a direct-buried concentric-neutral cable that is simply a bare neutral wrapped around the live conductor. I am not sure of the conductor type but I think the bare wrap is lead.
TOMWELDS
Member
- Location
- Westchester Cty. New York
Re: bonding metal street light poles
The utility here wants a ground rod at each pole connected to the pole's ground. Iv'e always done this anyway. Why would you want to jepordize safety by not grounding it in some manner? Gotta do it!..lol
The utility here wants a ground rod at each pole connected to the pole's ground. Iv'e always done this anyway. Why would you want to jepordize safety by not grounding it in some manner? Gotta do it!..lol
bphgravity
Senior Member
- Location
- Florida
Re: bonding metal street light poles
There is no added benefit or safety by adding a ground rod to a light pole, especially one served by a 120V circuit. The earth is not an effective fault path.
- Location
- Bremerton, Washington
Re: bonding metal street light poles
"The utility here wants a ground rod at each pole connected to the pole's ground"
As long as you realize for 120V this won't clear a ground fault. At 120V with 25 ohms your current to ground will be only 4.8Amps.
Utilites follow the NESC which is performance based for lighting, but for systems under 600V, following the prescriptive rules of the NEC would result in a safe installation, as an equipment grounding conductor would be installed.
Keep in mind many utilites started out in the lighting business in the early 1900's.
There is no reason to install a ground rod at a metal lighting pole if the pole has an equipment grounding conductor.
I'm on the Illumination Engineering Society Roadway Lighting Committee, and we write the standards for street lighting. Why are ground rods installed at street lighting poles?
Perhaps the best answer is "the civil engineer drives the bus on traffic signal installations".
Its just been done that way for a long time...
"The utility here wants a ground rod at each pole connected to the pole's ground"
As long as you realize for 120V this won't clear a ground fault. At 120V with 25 ohms your current to ground will be only 4.8Amps.
Utilites follow the NESC which is performance based for lighting, but for systems under 600V, following the prescriptive rules of the NEC would result in a safe installation, as an equipment grounding conductor would be installed.
Keep in mind many utilites started out in the lighting business in the early 1900's.
There is no reason to install a ground rod at a metal lighting pole if the pole has an equipment grounding conductor.
I'm on the Illumination Engineering Society Roadway Lighting Committee, and we write the standards for street lighting. Why are ground rods installed at street lighting poles?
Perhaps the best answer is "the civil engineer drives the bus on traffic signal installations".
Its just been done that way for a long time...
TOMWELDS
Member
- Location
- Westchester Cty. New York
Re: bonding metal street light poles
My post was "grounding the POST to earth". I wasnt talking about grounding the neutral wire. Electricity wants to go to earth. 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. That's why the utility here wants a ground rod at each pole. Each pole is treated as an individual. As for the neutral, If it's metered on private property, the neutral would obviously be grounded. On public roadways, where it's utility wiring, The neutral is not grounded. But by theory, if the neutral is not grounded, then it's not a neutral.
My post was "grounding the POST to earth". I wasnt talking about grounding the neutral wire. Electricity wants to go to earth. 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. That's why the utility here wants a ground rod at each pole. Each pole is treated as an individual. As for the neutral, If it's metered on private property, the neutral would obviously be grounded. On public roadways, where it's utility wiring, The neutral is not grounded. But by theory, if the neutral is not grounded, then it's not a neutral.
peter d
Senior Member
- Location
- New England
Re: bonding metal street light poles
Tom,
Electricity is not trying to return to the earth, it is trying to return to the source. It will take all available paths to get back to the source, and sometimes that includes the earth.
A ground rod will not eliminate dangerous touch potential of a light pole in the event of a fault. The impedance of the earth is too high to allow enough current to flow to trip an OCPD at low voltages. Primary voltage is another matter entirely and a ground rod is very effective at tripping an OCPD.
I also don't understand why you say the utilities "neutral" isn't grounded?
[ December 10, 2005, 12:27 PM: Message edited by: peter d ]
Tom,
Electricity is not trying to return to the earth, it is trying to return to the source. It will take all available paths to get back to the source, and sometimes that includes the earth.
A ground rod will not eliminate dangerous touch potential of a light pole in the event of a fault. The impedance of the earth is too high to allow enough current to flow to trip an OCPD at low voltages. Primary voltage is another matter entirely and a ground rod is very effective at tripping an OCPD.
I also don't understand why you say the utilities "neutral" isn't grounded?
[ December 10, 2005, 12:27 PM: Message edited by: peter d ]
Re: bonding metal street light poles
TOMWELDS, I second Peter's post.
Electricity does not "want to go to earth".
A ground rod can actually increase the danger around a pole.
Also, The utility neutral is usually muti grounded along it's path, I believe 4 times per mile if not more.
Roger
TOMWELDS, I second Peter's post.
Electricity does not "want to go to earth".
A ground rod can actually increase the danger around a pole.
Also, The utility neutral is usually muti grounded along it's path, I believe 4 times per mile if not more.
Roger
TOMWELDS
Member
- Location
- Westchester Cty. New York
Re: bonding metal street light poles
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.
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.
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