Pole Base Technique

[George Stolz]

I recently prepped some pole bases for a parking lot. I had less to do with this than I normally do, the GC apparently is taking care of most of the work. All I had to do was get my conduit in position, and tie a grounding conductor from the rebar cage they built and group it with the RNCs.

As I was proceeding, a fellow apprentice came out, saw my progress and asked me where the coil of wire was at the bottom. I replied that I wasn't asked to do so, the foreman simply wanted to use the cage as an electrode.

My coworker thought the coil of wire was code.

Every pole base he'd ever seen had a bare conductor coiled in the bottom, and attached to a cage (if present) and brought into the pole. Sort of a CEE, only in contact with earth on the bottom, concrete poured onto it.

I pulled up next to a fellow employee at a long stoplight, and asked him about it. He thought it was code too, from a different source.

Interestingly to me, the size of the wire varied, as the story goes. Some used #4, some used #6, some used even as small as #8.

Any ideas as to the source of this practice? If I remember a half-remembered discussion on CEE's in the past correctly, then the CEE came into the NEC around 1970 and the specifications never appreciably changed. My code knowledge starts in the 2002, which does me no good.

At one point in the discussion I thought that perhaps a trainer of today's foremen in the company started the "tradition", but one guy said he'd seen it in other companies as well. So, I figured there might have been a historical source for it?

Also, what is your Standard Operating Procedure?

All replies appreciated as always.

 

[iwire]

Who says you have to hook to the cage?

We do them a bunch of different ways, it all depends on the details shown on our prints.

No electrode at all, a rod with a conductor up to the pole, a rod cad welded to the cage with a 2 AWG and than cad welded to a j-bolt...


What ever 'they' want.

No matter what I don't think it makes a bit of difference, you have pole connected to 4 large j-bolts in direct contact with cement that is in direct contact with earth how much better is it going to get?

 

[mdshunk]

That coil of wire is an old NESC technique for line construction called a "pole butt electrode". I'll try to dig up some old pics to post...

 

[Pierre C Belarge]

George
This would most likely fall under 250.54 Supplementary Grounding Electrode.

 

[George Stolz]

Holy 3 replies in eight seconds, Batman!

What ever 'they' want.

If there is no spec, what do you do of your own free will? Just the anchor bolts? (Not that I'm saying there's anything wrong with that, to be clear. )

Marc, any links would be great.

Pierre, hopefully it'll be a Auxilliary electrode in 2008.

It was actually a really interesting discussion - we explored a lot of ground in a short lunch break. A pole being a "structure" (with reference to 225.32 exception 3 to clarify), 250.32(A) exception, and they came up with 410.15 while I was grabbing fast food (and sitting at stoplights).

It was a good Friday. Any day the codebook comes out is a good day. Not to say we lost any productivity over it, either.

 

[mdshunk]

Marc, any links would be great.

George, I just scanned in a few pics from my old handbook. Please note that there is some technique involved in installing this coil to keep it from acting as a choke, which you will read:

 

[iwire]

If there is no spec, what do you do of your own free will? Just the anchor bolts?

You bet, just the anchor bolts.

I really do not believe that any further steps to connect that pole and base to earth are needed or would do a darn thing to lessen the damage if lightning nails the pole.

(Not that I'm saying there's anything wrong with that,

Seinfeld?

What are you saying?

 

[George Stolz]

I really do not believe that any further steps to connect that pole and base to earth are needed or would do a darn thing to lessen the damage if lightning nails the pole.

I believe that every inch of copper, pop cans, what have you, that gets pitched into the bottom of the hole will make a minute difference in what goes down in the event of a lightning strike.

I also see a point of diminishing returns on the investment.

For you, the point of diminishing returns is the anchor bolts. For me, it's a ground rod driven half way into the earth, just for kicks. I'm curious to see what others do too.

For some guys I talked to on Friday, that point was a coil of wire thrown in the bottom of the hole. However, the same guys balked at the idea of driving seven 3/4" 10' CU-Clad ground rods into the bottom of the thing, connected to a ...

Seinfeld?

I'm sending you the doctor's bill for the elbow I just injured falling out of my chair.

 

[George Stolz]

Marc, I just looked at your pictures. At dial up, it was a long download, but worth it. What year is that handbook?

I hadn't thought of the choke factor - the guy I was talking to could visualize a benefit from forcing the lightning into a swirl, thinking that the energy dissipated from following a path like that would help.

I've never really understood the choke effect, but I kind of take it as a given.

Going back to that handbook, I'd be interested to know what it says at the bottom of that page about testing ground rods.

 

[mdshunk]

Going back to that handbook, I'd be interested to know what it says at the bottom of that page about testing ground rods.

That's a topic for another thread. (one mehtod involves the use of 5 amp fuses and fire hydrants, and another involves several stout screwdrivers and a 6 volt battery). Treat yourself to a copy of "The Linaman's and Cableman's Handbook". It's pretty much the comprehensive standard text for linemen, in much the same way that Richter's "Practical..." is for electricians. It is a very enlightening read. A little pricy, but you can find them on eBay pretty regularly.

 

[willdogyou]

Of all the parking lot lighting pole bases I have formed and poured I've never ran the copper directly in the concrete. Copper+ concrete is not a good combination. Oxidation would almost start immediately. We always run a pvc conduit out of the form to the ground rod and either cadweld or clamp it.
Have also had spec. details requiring concrete brick underneath the rebar cage to keep the rebar from coming in direct contact with the earth to inhibit corrosion.

 

[iwire]

Of all the parking lot lighting pole bases I have formed and poured I've never ran the copper directly in the concrete. Copper+ concrete is not a good combination.

You may want to rethink that position.

The NEC does restrict the use of aluminum conductors.

250.64(A) Aluminum or Copper-Clad Aluminum Conductors. Bare aluminum or copper-clad aluminum grounding conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum grounding conductors shall not be terminated within 450 mm (18 in.) of the earth.

There is no such restriction with copper and the NEC actually recognize 20' of bare 4 AWG copper encased in concrete as a concrete encased electrode.

250.52(A)(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.

 

[haskindm]

Corrosion is caused by oxidation. Oxidation requires air. There is very little air present in concrete so corrosion should not be a problem. That is why it is a little strange that many engineers spec that re-bar be encapsulated in epoxy; without air it will not corrode so the epoxy should not be needed.
Just my 2 cents.

 

[don_resqcapt19]

Oxidation requires air. There is very little air present in concrete so corrosion should not be a problem. That is why it is a little strange that many engineers spec that re-bar be encapsulated in epoxy; without air it will not corrode so the epoxy should not be needed.

There is plenty of oxygen in wet concrete and most concrete in contact with the earth stays wet enough for oxidation to occur.
Don

 

[iwire]

Is oxidation / corrosion that much of a problem with copper?

Ground rods are in direct contact with the earth and are often copper plate.

Ground rings are in direct contact with the earth and must be copper

Plumbers direct bury copper quite often....or a least they did until they could use plastic.

 

[Smart $]

Is oxidation / corrosion that much of a problem with copper?

Ground rods are in direct contact with the earth and are often copper plate.

Ground rings are in direct contact with the earth and must be copper

Plumbers direct bury copper quite often....or a least they did until they could use plastic.

I was told by an AEP engineer that oxidized copper is still a good conductor, and I have never had any reason to question that assertion. On that basis, there would be no concern as any encased oxidized copper will remain in place.

 

[tallgirl]

Marc, I just looked at your pictures. At dial up, it was a long download, but worth it. What year is that handbook?

I hadn't thought of the choke factor - the guy I was talking to could visualize a benefit from forcing the lightning into a swirl, thinking that the energy dissipated from following a path like that would help.

I've never really understood the choke effect, but I kind of take it as a given.

The choke effect comes from the changing magnet field caused by the change in current. The electro-magnetic field that's created by the lightning flowing through the grounding wire induces current into the wire and that tends to resist a change in voltage. So, instead of giving you a nice low resistance path to ground you'd wind up with a much higher resistance path due to inductive reactance. And, making matters worse, when the field collapses after the strike, current will be induced back INTO the wire.

Stapling the turns of the coil together makes it essentially not a coil.

It's the same physics principle that makes clamp-on amp meters work.