Boy, does that combination look strange!

It raises a question though: How is the grounding of the metal pole usually carried out in the U.S.? Is each pole just bonded to the neutral, or is a separate EGC run along the street?

Paul:
The majority of "street lighting" around here (NJ) is utility owned and maintained. Some is overhead, some is underground, and some is a mix of both. A recent "street scape" project (business area rehabilitation) job utilized utility installed decorative poles (metal) w/ lantern type HID luminaires. They ran PVC to the new poles from the OH grid, and ran triplex to each pole. The ground (earth) consisted of a driven ground rod at each pole.

The utilities also install & maintain parking lot lighting (site lighting). Some consist of metal poles, UG wiring from a pad mount transformer, triplex in the PVC, and a ground rod at each pole. Apparently, the utility is exempt from installing a grounding conductor "pole to pole", and also are not required to "bond" all the rods.

The poles are all individually controlled by a photo cell at each pole/fixture.

Hope this answers your questions.

PS: Almost forgot; I have not come across too many like the photos.
John

[This message has been edited by HotLine1 (edited 06-30-2003).]

No offense meant to anyone in eastern Washington, but this Snake River pic was a 500kV span over low-voltage contact wires serving a rolling crane.


[Er, NEC not applicable?]

Maybe the angle of the photo is deceiving, but there doesn't appear to be much clearance for half a million volts!

John,
Thanks for the info. It just looks odd to see overhead lines and insulators on metal poles. I don't ever recall seeing that combination before, even in America.

Over here metal lamp standards are always wired underground. Where lights are needed with overhead wiring, they're generally just individual bracket lamps fitted to each wooden pole (although overhead lines in areas built-up enough to have street lights have disappeared rapidly in the last 20 years or so).


Do you mean that the metal poles were connected only to a ground rod, and not bonded to the neutral in any way whatsoever? (What would be called a "TT" system here.) If so, then is the feed via a GFCI ?



[This message has been edited by pauluk (edited 06-30-2003).]

Paul, agreed the picture angle compresses the spacing of the two spans. There is about 25 feet between the two.

Paul:
quote:
--------------------------------------------------------------------------------
They ran PVC to the new poles from the OH grid, and ran triplex to each pole. The ground (earth) consisted of a driven ground rod at each pole.

To respond to your questions...

To the best of my knowledge, there is no GFI protection on our utility lines, as the 120/240 volts is obtained from pole mounted transformers. This 120/240 supplies various loads, street lights, site lights, traffic signals, and customers.

Again, as far as I know, the grounds (earth) for the poles is via a driven rod, unless the neutral from the triplex is tied to it inside the poles. I have no jurisdiction as AHJ on the utility equipment, and I have not seen the inside of these poles. We removed a utility metal pole (site lite) that was hit by a truck, and it's ground (earth) was only a driven rod. (120/208 volt feed in triplex in PVC)

Hope this answers your questions. Perhaps BJarney has some input; or one of the "line guys".
John

Thanks John.

I'm just looking at the situation from a purely technical view: If the post is grounded only to a local rod, then the loop impedance may well be high enough that a short wouldn't open any OCPD and would leave the pole hot. Not good.

I've got the same situation out in front of my place. OH duplex wire.
They're putting the utilities all underground right now. My street's ripped up, and a big pain in the tailfeathers.
(No access covers to the poles, I'll get a pic when they pluck the poles, and send it in)...S

Paul:
A side note; the only OCP that I know of is the primary fuses at the pots (transformers)
Or some pots have a resetable CB device built in. I have no clue of the ratings; the pots range from 25 to 75 KVA usually.
John

HotLine, it’s fairly common to provide overcurrent protection for street lighting in the form of a submersible fuseholder with a UL class-CC fuse. They can be hidden in subsurface concrete boxes or in pole bases at the handhole. In more recent underground-fed poles, typically municipalities specify an equipment-ground conductor routed with the circuit conductors. A ground rod or a ‘Ufer-like’ flat coil of ~6AWG solid copper at the concrete-form base is often called out, but as supplemental ground electrode for lightning protection. Think about it—metal light standards make superb “air terminals” (lightning rods.) An example of a submersible fuseholder is the Bussmann HEB-series part. http://www.bussmann.com/library/bifs/2127.PDF Littlefuse and Shawmut sell ‘em too.

For overhead duplex spans to metal poles, it’s possible to treat the situation as it if was a junior unmetered 2-wire service entrance, and bond the grounded-circuit conductor to the electrode and pole metal. Agreed that there may be older installations where a street-full of metal poles is served by a pair of unfused overhead ungrounded conductors, where a ground fault in a pole would not clear an overcurrent device. An old school of thought may have been that no overcurrent protection meant fewer outages, but discharge-lighting ballasts can blaze nicely if there’s no upstream overcurrent protection.

Properly sized streetlighting fuses have another feature—if a ballast craps out and its local fuse opens, the rest of the circuit still runs.

This ground rod or not to ground rod topic has been driving me nuts for the past month or so. I've been trying to get all the information I can on the subject. I need to install 10 light poles, ur, um, Standards. I have come to the concusion that the ground rods are not installed for short circuit ground fault protection but for lightning protection when installed with surge protection. The short circuit ground fault protection is supplied by the EGC ran with the circuit condutors. There should be no bond or connection beween the two other that what is made through the fixture, ur, um Luminare. Does it sound like I'm on the right track? If so, where do you put surge protection on a parking light circuit?

Blessings, Mark

Bjarney,
I'd agree with you on the fusing of street-lights, over here we use HRC fusing in each standard.
Hotline,
Using GFI protection on Line equipment would, to a certain extent, be a waste of time and money, in that, Insulators, by their virtue, attract dust during dry spells, when the air moisture level increases, this dust becomes damp and you have an instant tracking problem, that can cause a small leakage current to Earth, via cross-arms(wooden or metallic).
Even at Low Voltage, this can be a real problem.