Unsafe Installations at Metal Light Poles
Many of the traffic signals, school zone signals, etc. are designed and installed by those who are not correctly trained. Some time back our department had to inspect a new service to power a "school zone" flashing light. The service was located near one of the signs and fed it by an underground conduit. The other sign was 1/8th mile down the street and fed by overhead triplex. The electrical service was grounded by a rod driven at the pole and was proper. No ground wire was in the conduit across to the metal pole holding a sign and a flashing light.
The contractor said, "We NEVER put a ground there." The school called to inquire why we were obstructing "safety" by not allowing this (unsafe) installation to be energized.
The metal pole was on the corner and was located where children would stand and hold on to it before crossing the street. Live conductors open inside the pole and NO ground!
After extensive references to the NEC and preparing a report we finally convinced the contractor to pull a green #10 (to match the #10 conductors on the phases, even though on a 15 amp breaker) over to the pole. The far pole was grounded through the bare conductor on the triplex and the insulated conductor identified by a ridge was used as the grounding conductor.
The successful resolution of this required a major effort by the department. For something so simple as a (green) grounding conductor to electrical equipment!
I also knew of a project for 150 thirty foot poles lights at an interchange fed by 'hots' (do not know the voltage- probably 480) and NO equipment ground. The contractor told me that they required a 25 ohm ground from a driven rod at each pole but no equipment ground! The state was upset that the job was over time and over budget as they were driving 100' or more in the sand to get the 25 ohms.
How foolish! It did no good for safety or clearing faults. Was costly and could have been replaced by a grounding wire to each pole so easily.
A grounding wire to each pole, bonded to the pole and tied to the base by the anchor bolts would have been a fine ground plane- contact with the earth at each site to give a ground plane and tied to the service equipment and supply to clear fault current.
As installed, the separate ground rods did nothing.
Lynn Adams Investigator Escambia County Contractor Licensing
Mike Holts Comment: Lynn is 100% correct. A ground rod at a metal pole does not serve any purpose. What is needed is an equipment grounding conductor [250.118] installed with the circuit conductors [300.3(B)] that is bonded to each pole [250.4(A)(5). This ensures that dangerous touch voltage from a ground-fault will be quickly cleared.
By the way, I just received a paper that the Architects Institute of America (AIA) has a document called the Masters Something (dont remember the name) and they specify a ground rod at each pole! I cannot believe this. I wonder how long this document has contained this requirement. Where did they get there information to to place this in the document?
I also know that there is a document called the Masters XXXX and there is a Division 16 for electrical. If someone has access to this document, could you look and see if they specify ground rods at poles and let me know. In addition, I would like if you know of any other standard, like the Traffic Signal people or a Military standard and see if they specify ground rods at poles. Please let me know the page and section number and I will post this info on my site and make some comment about how this is a waste of time.
Oh, yea for those of you that are designing or installing ground rods, driving a ground rod at a metal pole serves no purpose. I have written about this many times. If you think I am wrong, please let me know why you think I am wrong by providing me with some document that explains why this should be done.
Once I have some time, Ill take each of the arguments like. Its to protect against lightning (like lightning is not going to hit the pole), help clear a fault (false), reduce touch potential to a safe level (false), protect the concrete base from cracking (false), prevent lighting from entering the building (false) and explain why these are false.
Hey, I love it when Im wrong, because I get to learn something new so if you think a ground rod at a pole serves a purpose, provide me with information to support your thoughts.
However, please do not waste you time to tell me what you feel (I already know that, I felt the same thing), just give me some facts to prove your position. Let us keep this dialog moving in a positive direction.
Forgive grammar or spelling errors, Im very busy but I wanted to get you this newsletter.
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