Adding a ground to existing 2 wire circuit.

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  #1  
Old 10-13-06, 01:17 PM
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Adding a ground to existing 2 wire circuit.

My home was constructed in the early 70's. It has a 1200ft dirveway and this concerns the lightposts along this driveway. At a high level, I am looking for advice on establishing a working ground for this circuit or parts of it.

Before the actual question, here are several facts about the current circuit:
1) Two 8 qauge aluminum wires leave the basement via buried conduit.
2) No 3rd ground wire leaves the basement
3) There are 5 light posts along the driveway.
4) Distance from house to pole 1 is 300-500ft (actual route of buried wire is unknown)
5) Pole 1 and pole 2 are each separately fed by these 8 gauge aluminum wires. (Only one set of wires leave the basement, but somewhere along the way there is a yet to be discovered junction where separate feeds branch off to each pole. This may be occuring at a place on the propoerty where overhead wires transition to underground, but I'm not about to dig anything up to check.)
6) Pole 1 wiring from metal junction box to light fixture is 8 gauge aluminum no 3rd wire ground
7) Pole 2 feeds pole 3 via a more conventional looking (to me anyway) 12 gauge 2 conductor copper wire with 3rd ground wire. The 3rd copper ground wire is attached to the metal junction box on pole 2. The light fixture on pole 2 is fed from the pole 2 junction box by 8 gauge aluminum wires with no 3rd wire ground.
8) Pole 3 is wired completely with 12 gauge 2 conductor copper wire with 3rd ground wire. Pole 3 feeds pole 4 and pole 5. Pole 3's ground wires are all connected to the metal junction box on pole 3 (there are 4 of them - feed from pole 2, feed to pole 3 light fixture, feed to pole 4, and feed to pole 5) .
9) Poles 4 and 5 are both wired the same way, which is as follows: Wired completely with 12 gauge 2 conductor copper wire with 3rd ground wire. Fed from pole 3. Feeding a light fixture. Feeding a GFCI outlet. Ground wires all connected to the metal junction box.
10) There is currently a short on pole 4.
11) The way the 3rd ground wire is hooked up, this creates a situation where touching the metal junction boxes on poles 2, 3, 4 or 5 results in a shock.
12) I am planning to replace the pole 1 and pole 2 junction-box-to-light-fixture 8 gauge wiring with 12 gauge 2 conductor copper wire with 3rd ground wire
13) This question does not relate to the joining of copper wire to aluminum wire or fixing the short on pole 4

The question:
- Is there a way for me to establish 2 working grounds (one for pole 1, and one for the current copper-ground-wire-connected poles 2, 3, 4 abnd 5) without replacing the 300-500ft of buried 8 guage aluminum wire coming from the house to pole 1 and pole 2?
- For example could I attach and bury a certain length or coil of copper grounding wire (like that used to ground my pool and pool heater) beneath pole 1 and pole 2, and be done.
- Or am I oversimplifying something that deserves the attention of an electrician.

Thanks for reading all of this.
 
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  #2  
Old 10-13-06, 01:38 PM
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> Is there a way for me to establish 2 working grounds
> For example could I attach and bury a certain length
> or coil of copper grounding wire

No, the only legal and effective equipment ground is a continous metal pathway back to the panel. Are the aluminum conductors in metal conduit? If so, the conduit may be an adequate equipment ground conductor.

The type of "ground" that the Earth provides is not the type of "ground" required for branch circuits.

> like that used to ground my pool and pool heater

Technically, what you do with a pool heater is "bonding" which is different than either Earth grounding or the equipment grounding situation here.

> Or am I oversimplifying something that deserves the
> attention of an electrician.

The concepts involved with grounding can be hard to understand. I think you can probably do this work yourself; but if those conductors don't have metal conduit, I don't see any way to make it happen without a trenching machine and a lot of new cable.
 
  #3  
Old 10-13-06, 01:57 PM
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First of all, thank you for your prompt repsonse. I appreciate your taking the time to respond as you did.

Unfortunately the conductors leave the basement in conduit but emerge conduit-less out of the ground at poles 1 and 2.
I may dig a little around the the base of the poles where the wires emerge to see if I strike any conduit. Because the single set of conductors branches off into separate sets for pole 1 and pole 2 at some point (probably where the feed from the street goes underground. It's above ground for 800 feet and under ground for 400ft), it wouldn't suprise me if the conduit ends at that point as well.

So it looks like it's time for a trenching machine and a lot of cable. And because the trenching will likely follow the path of the buried underground service from the house I think this may be out of my league. Tere's also 30+ years of woods growth over the route.

It might be easier and cheaper to just leave the lights off.

Thansk again.
 
  #4  
Old 10-13-06, 02:09 PM
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> It might be easier and cheaper to just leave the lights off.

Without a doubt! New #8 SEU aluminum cable would cost about $1/ft; over $1,000 just in cable.

Take a look at what is available in solar powered lamp posts. The posts charge up AA batteries during the day and use very high efficiency LED lights to glow many hours into the night. Once you buy the posts, it's free to run them plus no trenching or cable.
 
  #5  
Old 10-13-06, 02:26 PM
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Thanks again. Rechargeable LED lights are an excellent suggestion.
 
  #6  
Old 10-13-06, 02:45 PM
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Another question.

Most of the solar rechargable lighting I've seen has been ankle height for walkways.

Do you know whether solar rechargable LED lighting is available that can provide anything comparable to the illumination I'm accustomed to from my current 100w mecury vapor lamps atop 15ft poles.

Note: I admit that at the moment my mercury vapor lamps are providing no illumination at all. But let ignore that small detail for now
 
  #7  
Old 10-13-06, 06:10 PM
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A few ideas for you:

1. Have you checked with your utility regarding installing and maintaining driveway lighting? I know that here they will bear some of the capital costs in exchange for a fixed monthly charge for each fixture. However they will not do this for a receptacle.

2. Hire a private locator service to mark the wiring paths and get a depth estimate. Around here they are $100 an hour or so with a 1-hour minimum. Some have a trip charge. See if they can figure out where the conduit ends. If that's fairly far out, you may be able to put in a junction box and just run new ground wire from that point. Shut off the power and dig at the junctions and other important spots to see what you find.

3. I doubt you will find solar rechargeables that will provide more than a "marker" light, let alone illuminate an area.
 
  #8  
Old 10-13-06, 06:20 PM
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Thanks for the good suggestions regarding checking with the utility and hiring a locator service. I appreciate your taking the time.
 
  #9  
Old 10-14-06, 06:32 AM
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Based on the helpful replies to this thread I did some research and thought the following links might be helpful to others. They provided me with some easy to understand high level information as to why my understanding of "grounding" was too simplistic.

This first link does a good job explaining the difference between the white wire "grounded conductor" and the green/bare wire "equipment grounding conductor".

http://www.codecheck.com/grounding.htm

This second link references a discussion regarding the purpose of "bonding" swimming pool components.

http://www.codecheck.com/q_a_electric.htm#poolbonding

Thanks again to ibpooks for introducing me to the differences.
 
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