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Connecting copper ground wire to galvanized mast

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Old 12-19-2011, 09:47 AM   #1
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Default Connecting copper ground wire to galvanized mast

Wondering how most have dealt long term w/ connecting copper grd wires to galvanized masts?

Most masts are galvanized. Connecting copper to galvanized isn't recommended because of galvanic oxidation between (esp.) these 2 metals.

NEC requires (eventually) the antenna grd wire be directly connected or bonded to electrical service grd rod, which are almost always copper in this area. Mine is Cu.

Galvanized grd clamps for a mast * may * be available (so far, not locally to fit 1.5" mast). But still are connecting Cu wire to galvanized (zinc) clamp.

Could use a "corrosion prevention" compound product between dissimilar clamp & mast metals or wire & clamp. But most of these, if read the label / MSDS, contain either zinc or copper (some aluminum). Only diff is the compound, while still in tact, seals out moisture & oxygen. NOTE: many call these "conductive" anti-oxidant compounds. Per Noalox tech dept, it is ONLY conductive UNDER PRESSURE. Meaning, only the VERY thin layer between clamped surfaces is conductive. Then you still have a zinc based compound against Cu wire, or Cu based compound against galvanized pipe. The compound filling voids doesn't improve conductivity.

I tested conductivity (resistance) of several compounds containing zinc + graphite, Cu based, Al based. All showed 0 conductivity in a no pressure condition (exactly same as dielectric grease).

Could use Al grd wire & galvanized grd clamp on mast, but when get to copper grd rod, still have dissimilar metals issue. Even more problematic because of regular water splash & closeness to damp earth, splashing dirt onto connection, etc. ALSO NOTE: Noalox & similar compounds are intended for Al / Cu connections, per specs.

Most any compound gets squeezed out between the actual contact points of a wire & mast or grd rod, leaving the 2 dissimilar metals touching. Sure, a strong surge might blow right thru a diminished conductivity ground connection, but static discharge might not.

Using these anti-corrosion compounds for Cu wire (or bronze clamp) to galvanized mast may work well enough in practice to maintain conductivity & keep oxidation to a minimum. What are others' experience on this? Course, the real test is how a connection performs during an actual lightning surge.

Thanks.
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Old 12-19-2011, 12:47 PM   #2
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Bonding and grounding between galvanized steel and copper is done all the time on telco equipment. Any corrosion due to electrolysis is very slow. We (telephone techs) don't do anything other than clean the two surfaces before installing a ground strap or clamp.
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Old 12-19-2011, 01:20 PM   #3
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Thanks - I do realize that. However, it's still not "recommended." That doesn't mean it may not work - esp. if use some type anti-corrosion compound. Most of those products say, to effect: "prevents corrosion / oxidation in aluminum to copper AND OTHER connections."

They don't say * WHAT * other. My phone ground wire, connected to the electric service grd wire is greenish black & so is the service grd wire. I haven't tested conductivity. From what I've read many times (never seen qualified data), a large % of surges entering homes come thru phone lines. Dunno.

If any truth to that, I'd guess has something to do w/ the phone grd wire from demarc is very, very small. It wouldn't handle any kind of large surge, no matter how good a connection. On mine & many houses I've seen, phone grd wire MIGHT be # 16, at best. Simply too small to handle any kind of surge.

I'm sure some members will eventually read this that've had copper (or bronze clamps) connected to galvanized masts, using some method to slow down oxidation.
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Old 12-19-2011, 02:07 PM   #4
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The products that help protect the dissimilar metals from reacting w/ eachother is doing nothing more than preventing O2 from acting as a catalyst. Some actually have bits of nickel, or copper filings that imbed themselves in the two surfaces.
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Old 12-19-2011, 02:17 PM   #5
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Quote:
Originally Posted by toandeaf View Post
Using these anti-corrosion compounds for Cu wire (or bronze clamp) to galvanized mast may work well enough in practice to maintain conductivity & keep oxidation to a minimum.
I'd vote for bronze or tin plated brass clamps. http://www.harger.com/library/brochu...ine%20Card.swf

Tin plated clamps can also be used with aluminum wire. If you opt for aluminum wire it should be brushed clean and coated with Noalox or similar anti-corrosive compound.
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Old 12-19-2011, 04:50 PM   #6
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Thanks & thanks.

Of the anti-oxidant products I've seen ingredients, zinc is most common because it's most reactive - even more than Al, so it will corrode 1st. Other metals might be used for diff applications. However, unless the zinc in the compound reacts faster than zinc on galvanized conduit, the conduit would still oxidize. How fast & to what extent to affect conductivity is unknown. Most tables I've seen on galvanic reaction show it accelerates in water (lots of rain) or saltwater. I'd then assume keeping moisture & most 0_2 out would slow oxidation.

Thanks for link. I've found the selection for 1.5" grdg clamps is pretty slim - esp. locally. Bronze is available.
Actually, depending on the bronze alloy, some bronzes (ALUMINUM BRONZE (CA 687)) would be less reactive w/ zinc than tin, according to one chart. That surprised me.

I have some zinc strips from a chem lab that I could put between mast & bronze clamp, though I'm not sure about their strength & zinc oxidizing away over time. I guess it'd be OK as long as tightened connection every couple yrs.

Last edited by toandeaf; 12-19-2011 at 05:10 PM.
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Old 12-20-2011, 07:30 AM   #7
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The bottom line is the OP is right.
When you connect a copper ground wire directly to a galvanized mast pipe - if the pipe was in contact directly with the earth, the whole system would turn itself into a simple battery with the anode being the ground rod and the charge between the two - the galvanized product on the outside of the pipe being the consumable material - just like a zinc battery.

The way that people in the communications industry gets around this is to use a simple stainless steel clamp - which looks like a hose clamp - but has a inner and outer ring.
The inner ring touches the galvanized pipe and does no harm.
The copper wire goes between the inner and outer ring and does not touch the pipe - but has enough conductivity to work as intended.

http://www.dxengineering.com/Section...&DeptID=19#Top

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Last edited by JB Antennaman; 12-20-2011 at 08:02 AM.
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Old 12-20-2011, 11:48 AM   #8
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Thanks again, all. For those interested in JB's link & the clamp, here's one direct link w/ pic: http://www.dxengineering.com/Parts.asp?ID=915&PLID=103&SecID=51&DeptID={DBD52E0 0-E4FA-4BB0-A7B9-1EDCD8FCDE17}&PartNo=PPC-TK-1

Though, from this source, one clamp + shipping would be high.
They state the exact type stainless alloy, but most times, consumers wouldn't have that info. Depending on exact alloy of ANY metal, I found it can fall much farther up / down list of most / least noble metals. See attachment chart.

Could be easiest way is cover entire connection well w/ anti-corrosion compound. But according to this & other charts, even tinning the copper wire w/ tin-lead solder would be less reactive than copper to galvanized (zinc) or even silicon-bronze alloy to galvanized. Conductivity of anything added - like tin-lead solder - needs consideration. Tin-lead solder has high electrical conductivity, per http://www.frymetals.com/products/ti...roduct=tinlead . Could be tested.

No idea which bronze alloy typical electrical grd clamps are, but assume (uh - oh) they're mgf'd to be less reactive w/ Cu, meaning silicon-bronze. But silicon-bronze wouldn't be least reactive w/ galvanized. Stainless clamps, tinned copper wire & anti-oxidant are sounding better.
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File Type: zip galvanic reaction chart 127.zip (21.6 KB, 0 views)
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