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er is used to connect that neutral to the metallic enclosure of the pedestal. The main bonding conductor creates or is the beginning of the EGC.

Photo 2. A typical service pedestal used to supply street lights in a private community

There are a few ex-ceptions found in NEC 250 Part XI, but, generally, all metallic enclosures that contain elec-tric conductors or loads supplied by the service must be bonded to the service by the EGC. The EGC usually takes the form of a metallic raceway or separate grounding conductor installed with the circuit conductors (figure 2). NEC 250.118 provides a list of all permitted EGCs. The key point here is that the EGC is created at the electrical service. It does not exist on the supply side (utility) of the service disconnect; it is only installed on the load (customer) side.

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Are Your Streetlights Grounded? . . . Continued form page 32

Without an EGC, protection from electrical shock is de-pendent on the concept of “touch voltage.” If the met-al pole becomes energized through a fault in the pole or attached luminaire, the earth around the pole should be at a similar potential (voltage).

The voltage drop between the pole and earth will increase as the distance from the faulted pole increases. When a person comes in contact with the pole through his/her extremities (usually arms or hands), the shock voltage is limited by the arm length, which is why the phrase “touch voltage” is used. The electrical shock voltage is limited because a person touching a faulted metal pole must be close enough to the pole to touch it, and the point where the person contacts the earth (through the feet) and the pole (through the hands) is likewise limited.

Regardless, there is no low-impedance path for the ground-fault current without an EGC, so the faulted metal pole and the earth around it will stay energized until the ground fault is noticed and repaired. A person in con-tact with a faulted pole will probably still feel the elec-trical shock, but the “touch voltage” theory is reliant on the shock voltage being low enough so that the electrical current through the body will never rise to a danger-ous level. The injuries and deaths that occur every year suggest that the performance standard of the NESC is not always attained.

There are other variables which can affect the amount of current that flows through the human body. Wet earth and or a wet pole can increase the ground-fault current. Is the person barefoot or insu-lated from the earth by shoes? While dry skin has a fairly high resistance, wet skin or

any open cuts or abrasions on the skin reduces resistance and, thereby, increases the electrical current through the body, even if the touch voltage has not increased.

Load-side connectionStreetlights serving many private communities typi-cally get their electrical pow-er from a metered service pedestal (photo 2). The ser-vice pedestal and load-side circuits/equipment are in-stalled under the prescriptive rules of the NEC. Part XI of NEC Article 250, Equipment Grounding and Equipment Grounding Conductors, pro-vides the rules for EGC instal-lation. The service pedestal will have a connection point for a grounding electrode, where the grounded neutral conductor is connected to earth. A main bonding jump-

Figure 2. Fault-current path with an equipment grounding conductor

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quired. The installers thought that a grounding electrode (ground rod) installed in the site junction box, adjacent and bonded to the streetlights, would accommodate any problem (photo 3).

Photo 3. This equipment grounding conductor was not installed with the branch circuit to the service pedestal in the conduit (top left). The streetlight was “grounded” by a connection to the ground rod only (bottom right conduit) in violation of NEC 250.4

Even a large nationwide build-er-developer had to be con-vinced an EGC is required. In some neighborhoods, an EGC had been installed in the PVC conduit system, but it was never connected to the

light pole base or pole top luminaire(s). Since the developments were private, inspection and certification of the installed streetlight electrical systems was the responsibility of the developer’s engineer of record. But, an inspection by a qualified electrical inspector was never done. Unfortunately, situations such as this occur too frequently.

Are Your Streetlights Grounded? . . . Continued form page 34

NEC 250.24(C) requires the grounded neutral service conductor to be installed and bonded to each service disconnecting means, even if the neutral is not needed to obtain the voltage required by the premises electrical sys-tem. The grounded neutral service conductor provides a low impedance path for fault current back to the source (utility transformer). If there was no grounded neutral service conductor, the earth between two grounding elec-trodes (one located at the util-ity transformer and the other at the service disconnecting means) would have to be relied on to carry any fault current from the premises electrical system back to the utility transformer. The earth is usually a poor conductor of electricity, so the fault current may not be able to rise to a high enough level to open the overcurrent device that pro-tects the circuit. NEC 250.4 prohibits the use of the earth as an effective ground-fault current path.

No equipment grounding conductorUnfortunately, there are many instances where metal poles for streetlights located in gated or private communities around the country have no connection to the EGC. These streetlights are typically sup-plied by service pedestals and do not have utility-side connections. (figure 3).

In two documented instanc-es, electrical contractors who had installed street light systems did not even know that EGCs are required in PVC conduits. For many years, the contractors had been used to installing these systems on the utility side of the service where EGCs do not exist. When the contrac-tors made the transition to installations on the customer side of the service, they were not aware an EGC was re-

Figure 3. Fault-current path without an equipment grounding conductor

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Are Your Streetlights Grounded? . . . Continued form page 35

Public parking lots for large “big box” stores are not immune to the problem either. A recent final inspection in one location revealed that the branch-circuit EGC was not installed in the PVC conduits that supplied several dozen 40-foot parking lot luminaires for a large, nationwide retail store. The parking lot lighting for this store was designed and installed under the jurisdiction of the NEC and was supplied by branch circuits from a metered service pedestal (photo 4).

Photo 4. The parking lot luminaires shown here were supplied by load-side branch circuits that did not include an equipment grounding conductor. The installers thought that a ground rod installed adjacent to each pole would accommodate the problem.

Why did the installers leave out the EGC to the luminaires? Just as with the private communities, they were confused as to the difference in grounding requirements between circuits on the load-side vs. the supply-side of electrical services. The installers also thought that, with a grounding electrode (ground rod) installed at each pole, no EGC would be needed.

Auxiliary grounding electrodes are permitted by NEC 250.54, but this section makes it clear that the electrode must be bonded to the EGC, and the earth shall not be used as an ef-fective path for ground-fault current.

When such deficiencies are identified, they must be cor-rected by installing any missing EGCs in the PVC conduits and connecting them to the light pole base ground lug and the pole top luminaire(s) and by confirming connection of the main bonding jumper in the service pedestals.

What about your community? Are there streetlights that receive their electrical supply from service pedestals in your community? Have the pedestals and streetlight circuits been inspected by trained, qualified inspectors?

Situations like the ones described here prove the need for and the importance of trained electrical installers and inspectors. We can never become complacent and forget the basics of safe electrical installations. The bottom line is that, whether you follow the NEC, the NESC or just plain common sense, appropriate wiring methods, correct bonding, grounding and overcurrent protection are basics that cannot be ignored. Sarah and her friends are counting on it.

Pete Jackson is the chief electrical inspector for the city of Bakersfield, California. Beginning his career in 1980, Pete worked up through the ranks of the electrical indus-try as an apprentice, journeyman, foreman and general foreman. He was co-owner of an electrical contracting firm for ten years prior to joining the Bakersfield Building Department in 2005 and holds five electrical inspector certifications through the IAEI and ICC. He instructed apprentice and journeyman electricians through the Kern County JATC for seven years. Pete holds memberships in IAEI, NFPA, ICC, IBEW and serves as an AHJ repre-sentative on over twenty Standards Technical Panels for Underwriters Laboratories.

Really!

Submitted by:Rick Bergholz, TAPCO

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