Light Poles and Grounding Electrodes
- Thread starter iwire
- Start date
- Status
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Light Poles and Grounding Electrodes
Roger the problem with odds is the random kayos. You might hit the lottery in 14,000,000 tries but since the randomness steps in you might not. as the only way to make this a guarantee is to play all possible numbers. and we just can't do that with lightning.
Roger the problem with odds is the random kayos. You might hit the lottery in 14,000,000 tries but since the randomness steps in you might not. as the only way to make this a guarantee is to play all possible numbers. and we just can't do that with lightning.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Light Poles and Grounding Electrodes
I depends on which way the wind is blowing.
LOL
I depends on which way the wind is blowing.
Re: Light Poles and Grounding Electrodes
Roger,
You welcome!
I made some estimates regarding your building.
Let its collection area be 9,625 sqm.
Then, in 50 years, taking N= 11 flashes/year/sqkm,
the likelihood your building being struck:
At least once is 99,5%.
At least twice : 96,8%.
At least three times : 89,8%.
At least four times : 77,3%.
At least five times : 60,9%.
At least six times : 43,5%.
At least seven times: 28.5%.
At least eight times: 16,5%.
At least nine times: 8,9%.
At least ten times: 4,4%.
At least eleven times: 2,0%
At least twelve times: 0,5%.
As can be seen, the probability of being struck depends on the collection area and on the ceraunic level of the region(Td = 90 thunderstorm days per year) which implies N= 11 flashes/year/sqkm) by the formula:
N=0,04*exp(1,25*Ln(Td)).
Roger,
You welcome!
I made some estimates regarding your building.
Let its collection area be 9,625 sqm.
Then, in 50 years, taking N= 11 flashes/year/sqkm,
the likelihood your building being struck:
At least once is 99,5%.
At least twice : 96,8%.
At least three times : 89,8%.
At least four times : 77,3%.
At least five times : 60,9%.
At least six times : 43,5%.
At least seven times: 28.5%.
At least eight times: 16,5%.
At least nine times: 8,9%.
At least ten times: 4,4%.
At least eleven times: 2,0%
At least twelve times: 0,5%.
As can be seen, the probability of being struck depends on the collection area and on the ceraunic level of the region(Td = 90 thunderstorm days per year) which implies N= 11 flashes/year/sqkm) by the formula:
N=0,04*exp(1,25*Ln(Td)).
Re: Light Poles and Grounding Electrodes
Saadt, I think we would need to throw these "probabilities" out and use the existing occurances for a control. With this being the case and if they hold true, this structure would be due for 35 confirmed strikes in the next 50 year period.
BTW, all joking aside, I have talked with people who lived in this home as far back as the 50's, and it has frequently been hit by lightning strokes as far as all the parties remember.
In the time we have owned this home, I have discovered it pretty much sits on a Mica insulator.
Roger
Saadt, I think we would need to throw these "probabilities" out and use the existing occurances for a control. With this being the case and if they hold true, this structure would be due for 35 confirmed strikes in the next 50 year period.
BTW, all joking aside, I have talked with people who lived in this home as far back as the 50's, and it has frequently been hit by lightning strokes as far as all the parties remember.
In the time we have owned this home, I have discovered it pretty much sits on a Mica insulator.
Roger
charlie tuna
Senior Member
- Location
- Florida
Re: Light Poles and Grounding Electrodes
from everyone's expieriance---tell me how the additional ground rod has reduced damage caused by a lighning strike? in my fourty years in the trade i have worked on about fifteen lightning strike repairs -- they say "lightning is unpredictable" and that is true in my oppinion!
about five of these strikes concerned parking lot lighting systems. two without ground rods on older installations, and three with ground rods. the damage is the same --- blows up the lighting contactor and damage the source breaker or panel and sometimes the timeclock controlling the contactor. the ground rod and the conductor connecting the ground rod back to the power source's ground system is untouched, while the conductors feeding the pole are "fried"! and i don't agree with labelling a light pole a "structure"! if this is the case, every outdoor junction box and disconnect switch would also be a "structure"! since lightning is unpredictable - we can never say for sure that the ground rod has
reduced damage. since this practice started, i have not seen a reduction in damage to lighting systems by the installation of a ground rod. "our" industry needs to consider the safety issue of this additional ground rod and associated "green wire" inside the pole's connection space! too many people across the united states are being killed by "ungrounded" street lights. remember, most of the repairs and maintainance to these systems are performed by unqualified personnel. too many times, the "geen wire" from a ground rod is considered to be "the" power system's return ground path --- and someone gets electricuted. for this reason, an evaluation of this additional ground rod should be conducted and if not found to be a "proven" wiring method that helps reduce lightning damage --it should be outlawed!!!
from everyone's expieriance---tell me how the additional ground rod has reduced damage caused by a lighning strike? in my fourty years in the trade i have worked on about fifteen lightning strike repairs -- they say "lightning is unpredictable" and that is true in my oppinion!
about five of these strikes concerned parking lot lighting systems. two without ground rods on older installations, and three with ground rods. the damage is the same --- blows up the lighting contactor and damage the source breaker or panel and sometimes the timeclock controlling the contactor. the ground rod and the conductor connecting the ground rod back to the power source's ground system is untouched, while the conductors feeding the pole are "fried"! and i don't agree with labelling a light pole a "structure"! if this is the case, every outdoor junction box and disconnect switch would also be a "structure"! since lightning is unpredictable - we can never say for sure that the ground rod has
reduced damage. since this practice started, i have not seen a reduction in damage to lighting systems by the installation of a ground rod. "our" industry needs to consider the safety issue of this additional ground rod and associated "green wire" inside the pole's connection space! too many people across the united states are being killed by "ungrounded" street lights. remember, most of the repairs and maintainance to these systems are performed by unqualified personnel. too many times, the "geen wire" from a ground rod is considered to be "the" power system's return ground path --- and someone gets electricuted. for this reason, an evaluation of this additional ground rod should be conducted and if not found to be a "proven" wiring method that helps reduce lightning damage --it should be outlawed!!!
Re: Light Poles and Grounding Electrodes
I know this subject has been beat to death, and at my former employer I was forced to integrate the light poles in the parking lots into the building GES system. The main reason for doing this was to add protection to the security equipment mounted a top of the poles.
As I asked before what is the difference between a light pole and a communication tower. Ron and John hit on some of the differences. Ron pointed out shouldn?t the ground rod be integrated into the building GES if used, and John pointed out the pad provides a sufficient Ufer ground and a rod would be in the sphere of influence. To John I would agree and disagree. If the rod were set beside the pole I would agree. If the rod were set below the pad, I disagree, but it is a mute point.
So the main differences between a light pole and tower is 1. Tower GES system is integrated into building and property GES system. 2. All signal cable shields and power are multi-bonded to the tower especially where they leave the tower. 3. Most importantly all cables entering the building enter at approximately the same point the AC service and all outside plant cables employing SPG and using a surge protection devices bonded to the GES to discharge the ungrounded conductors.
So what techniques can be economically employed and what is not necessary:
1. IMHO an additional rod is not necessary, as I do not believe it adds any value unless it can be integrated into the building GES via radial, it?s just a light. However there is no real harm done by adding one other than expense, and if used set it below the pad as not to be in the sphere of influence.
2. Most importantly, if lightning is a concern, simply add a TVSS or surge device where the circuit enters the building and referenced to the GES, and another one in the panel serving the branch circuit. It is preferable the circuit enter near where the AC service enters to aid GES access. As Charlie Tuna pointed out even if the pole does have a rod, if the pole is struck, a charge will be induced onto the ungrounded and grounded circuit conductors, and will appear inside the building looking for a place to equalize/discharge. Give it a place or two to discharge rather than letting it find it?s own path through the distribution system and/or equipment.
OK, I will shut up now
I know this subject has been beat to death, and at my former employer I was forced to integrate the light poles in the parking lots into the building GES system. The main reason for doing this was to add protection to the security equipment mounted a top of the poles.
As I asked before what is the difference between a light pole and a communication tower. Ron and John hit on some of the differences. Ron pointed out shouldn?t the ground rod be integrated into the building GES if used, and John pointed out the pad provides a sufficient Ufer ground and a rod would be in the sphere of influence. To John I would agree and disagree. If the rod were set beside the pole I would agree. If the rod were set below the pad, I disagree, but it is a mute point.
So the main differences between a light pole and tower is 1. Tower GES system is integrated into building and property GES system. 2. All signal cable shields and power are multi-bonded to the tower especially where they leave the tower. 3. Most importantly all cables entering the building enter at approximately the same point the AC service and all outside plant cables employing SPG and using a surge protection devices bonded to the GES to discharge the ungrounded conductors.
So what techniques can be economically employed and what is not necessary:
1. IMHO an additional rod is not necessary, as I do not believe it adds any value unless it can be integrated into the building GES via radial, it?s just a light. However there is no real harm done by adding one other than expense, and if used set it below the pad as not to be in the sphere of influence.
2. Most importantly, if lightning is a concern, simply add a TVSS or surge device where the circuit enters the building and referenced to the GES, and another one in the panel serving the branch circuit. It is preferable the circuit enter near where the AC service enters to aid GES access. As Charlie Tuna pointed out even if the pole does have a rod, if the pole is struck, a charge will be induced onto the ungrounded and grounded circuit conductors, and will appear inside the building looking for a place to equalize/discharge. Give it a place or two to discharge rather than letting it find it?s own path through the distribution system and/or equipment.
OK, I will shut up now
- Status