Public Lessons Learned Entry: 0552
Lesson Info:
- Lesson Number: 0552
- Lesson Date: 1997-05-21
- Submitting Organization: JSC
- Submitted by: L. Underwood
Subject: Potential Electrical Shock Hazard Involving Light Poles on Streets and in Parking Lots
Description of Driving Event: Several randomly sampled exterior street and parking lot light poles were found to have defective electrical grounds that could result in a potentially lethal electric shock hazard if the pole is touched by a person.
The hazard is primarily a result of two conditions:
- The original design of the power distribution circuit lacked an equipment grounding conductor even though the installation met the National Electric Code at the time.
- The normal breakdown over time of the materials utilized in the supplemental ground rod which was installed to correct the original design deficiency.
The poles are energized primarily at night, but can be remotely energized for testing and repair during daylight hours. Certain power distribution system failure modes may result in an energized light pole. While it is unlikely to have a combination of a defective grounding condition and a power system fault, the condition can be lethal if the pole becomes energized. However, the shock hazard can be precluded by the installation of an upgraded supplemental ground to the earth.
Lesson(s) Learned:
Supplementary electrical grounding protection for streetlamp structures must be periodically verified.
Recommendation(s):
All personnel should understand the electrical shock hazard presented by an energized light pole. Therefore, do not touch street or parking lot light poles!
Immediate interim measures are being implemented, as follows:
- new ground rods are being installed on each light pole on-site,
- a temporary means of insulating the base of each pole is being examined
- a preliminary report has been requested that will make recommendations for permanent repair or replacement of the existing exterior lighting system.
Approval Info:
- Approval Date: 1997-05-22
- Approval Name: Ronald A. Montague
- Approval Organization: NA3
- Approval Phone Number: 281-483-8576
Mike’s Comment: Here’s another example where the industry recommends that we drive ground rods (supplementary electrodes – 250.54) for the purpose of reducing electric shock from a ground fault. The statement “However, the shock hazard can be precluded by the installation of an upgraded supplemental ground to the earth.” Is 100% false.
What is required is that an equipment grounding (bonding) conductor be bonded to every metal pole as required by the NEC so that all metal parts are bonded to an effective ground-fault current path [250.2 and 250.4(A)(3)].
I just can’t believe that we (me included) as an industry ever thought that a shock hazard could be precluded by the installation of an upgraded supplementary ground to the earth! Oh well… maybe my work will make a difference in educating the industry as to the danger of this type of thinking.
