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Silicon Bronze - use in outdoor grounding copper bus bar applications?

Situation: Outdoor antenna mast copper ground bus bars. The building inspector(s) usually request that "nuts and bolts" hardware co nnection to these copper bus bars (often just plated) be coated with anti-g alvanic compound. (Which I assume to be conductive grease?)

And, I don't think they mean "NoAlox" brand (and similar) copper-to-aluminu m protective coatings as is often used in the electrical trades.

So that got me to thinking about Silicon Bronze hardware. It's not as conductive as copper (only about 7% or so), but it's non-corros ive like many stainless steels. Also, Silicon Bronze hardware is non-magne tic, not that it matters for our application.

I am wondering if I can make the case to the inspector(s) that Silicon Bron ze hardware can be used WITHOUT having to apply any goopey-grease (NoAlox, ???, or otherwise), and still have a long-term, reliably conductive ground path for lightning strikes, etc...

I would like to get away from having to apply compounds altogether because our installers typically don't do it correctly in the first place, then the y manage to get remnants of the goopey stuff all over the rest of the proje ct. Plus, I have my doubts as to how long any substance applied to an outd oor copper grounding bus bar is going to last in salt-air coastline install ations (or otherwise).

What do you guys think? Is there an argument to made to use Silicon Bronze? And if so, are there any references you can point me to? Thanks!

Reply to
mpm
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Aluminum bronze is more conductive and corrosion resistant. Gotta run.... details later.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

On Apr 22, 2018, mpm wrote (in article):

As for copper ground bars, the electrical folk use copper plated steel rods driven six feet into the dirt, with a mechanical clamp attaching solid wire to ground rod, so I don?t understand the Inspector?s thinking here.

.

. I think that I would ask the Building Inspector what he meant, and what problem he is trying to solve, to avoid lost motion and money.

Joe Gwinn

Reply to
Joseph Gwinn

How did a building inspector get involved with antenna grounding?

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

It would useful knowing what manner of antenna mast or tower is involved and if for residential or commercial service. My guess(tm) is that it's a residential mast or tower ground, which is found in NEC

810 and is independent of the building ground, and the building electrical ground.

NEC Article 810 online: You will be asked to create a free account and sign in. Start at Chapter 8. This is for reading online only. Downloading and printing are not allowed.

A much more readable version: Article 810 - Radio and Television Equipment

A few comments:

The perimeter ring concept is described in Section 250. NEC 250.56 Grounding and Bonding recommends ground resistivity of 25 ohms or less: I once borrowed an AEMC 3730(?) clamp on ground resistance tester to check some of my sites at the demand of the insurance carrier: With good soil, the grounding met the spec. On sand or rock, it failed miserably which eventually required adding additional ground rods. My house also failed ground, but it wasn't worth fixing because I'm surrounded by 150ft redwoods and a direct hit to the house is very unlikely.

The typical direct burial ground rod clamp is made from phosphor bronze and uses a silicon bronze screw: You can identify red silicon bronze by the reddish color: As I understand it, the clamp is expected to survive a lightning hit. It might fuse from the very high current at some point, usually the point of highest resistance, which may be the connection between the clamp and the copper clad steel ground rod. The selection of phosphor bronze for the clamp was based on obtaining the lowest contact resistance, which yields the lowest heating, which translated into the best survivability from a lightning hit.

Please ignore my suggestion of using aluminum bronze. It's stronger and can be heat treated, but is also not very ductile (flexible) and therefore will have problems maintaining clamping pressure:

For lightning protection of a residential antenna pole or tower, I suggest you do not get creative.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Agreed!

This is commercial. (Building rooftops, not towers.) In some jurisdictions, the AHJ is quite literally the fire chief. (Don't a sk.)

Others in this thread are attempting to give an education on how to properl y construct a full facility lightning suppression system, while still other s are explaining electrical safety grounds under NFPA-70 Article-250.

That's not what I'm asking about.

I'm just interested in the connection hardware of the down conductor (which is usually #2 AWG) to the locally installed copper ground bus bar. Occasi onally, a project will call for #00 or 4" flat copper Centaur strap. (which can be much better when it comes to suppressing VHF band radio noise). Bu t again, none of that is what I'm asking.

All I want to know is whether Silicon Bronze hardware is suitable for the a pplication (I think it is, or "might be"?), and by using it, can we avoid h aving to use anti-galvanic compounds on the connections.

I am aware of exothermic grounds (Cad-welding). It's an expense and training issue I'd rather not deal with given that the vast majority of our inspectors/AHJ's are not (yet) calling for it.

Shhhh!! :)

Thanks

Reply to
mpm

Ahem... Your VHF radio "noise" is my commercial 2-way radio revenue stream. At VHF frequencies, the grounding system looks like a big long inductor and does nothing for grounding any stray VHF signals.

What is a Centaur strap? I couldn't find anything with Google.

My guess(tm) is you're building a comm shelter for cellular on a rooftop. I've never done that. All the buildings and boxes that I used to deal with are on the ground.

The typical copper grounding plate is annealed copper alloy 110 (or C11000) selected because of its high conductivity:

If you're going to connect to it with tin plated copper lugs, you're going to need something that protects the joint against galvanic corrosion. If you use unplated copper lugs, methinks you'll do better.

By hardware, I guess you mean the mounting hardware for the copper grounding plate. Looking at galvanic series table, Cu is -0.3 to -0.4V Si and P bronze are -0.3V Al bronze is -0.35 to -0.45V. The rule of thumb is that anything with less than 0.2V difference is compatible, making all the bronzes compatible with copper. So, for galvanic compatibility, I think you're safe using any kind of bronze hardware. As for strength, both Si and Al bronze are used for marine hardware (nuts and bolts) so either should work. Just stay away from tin plating, stainless steel, and galvanizing.

I think Si bronze hardware is ok, but I would appreciate not being sued for giving you bad advice. Please double check.

What's an AHJ?

Guidelines for the Use of Copper Alloys in Seawater See table 1.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

D'ya want to rethink that? :-)

Namely, a lack of ductility means it withstands /more/ stress without _permanently deforming_. The elastic deformation, which holds the clamping pressure, has a wider range, making it better. :)

That's the problem with pure aluminum, it's too damned...puttylike!

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: https://www.seventransistorlabs.com/
Reply to
Tim Williams

Maybe. My thinking is that if the clamp was too ductile, it would cold flow and lose some of the compressive pressure on the wire bundle as applied by the screw. Also, it was insufficiently ductile, it would be brittle and break instead of stretch under tension.

Looking at various commercial clamps, many are built so that the frame will deflect slightly when tightened: The deflection is tiny but the designs mostly seem to have the same idea. Methinks that this is intentional and done to simulate a spring. I don't know what mechanical design criteria is required for an electrical grounding clamp, but I'm fairly sure it would not be acceptable to have the clamp lose compression on the wire bundle and fall apart (especially if buried).

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

The primary purpose of the grease, anti-galv or otherwise (any grease is much better than none), is to make the connection contact surfaces gas tight, to prevent corrosion in between the contact surfaces. When clean surfaces which mate well are adequately tightened there is very little grease left in the interface, filling in the low spots between the high spots which actually make contact. A greased connection will last far longer than one assembled without grease in corrosive conditions.

Years ago I read both books in print on electrochemical machining. Electrochemical machining is electrochemical corrosion of the workpiece (anode) with a die (cathode), with an electrolyte pumped through the interface, and hundreds to tens of thousands of amps of current between them. Corrosion of electrical connections subjected to electrolyte spray was initially a big problem, until they started using grease and eliminated all stainless steel parts, which can look perfect even after losing all strength due to inter-granular corrosion. Greased connections have been working well for me for years in marine environments. Just because no grease is externally visible and the outside surfaces of the connection are badly corroded do not mean that the grease is not still working in the interface.

Use parts listed for the application, installed with all components properly cleaned, greased and torqued per mfgr's spec.

Minor aside, I recall also an article which claimed that in a typical tower mounted on the ground situation, lightning downconductors were completely useless because their impedance to lightning is much higher than the steel tower, which has much more surface area. Probably true, but won't exempt you from the requirements of NFPA 780 - Standard for the Installation of Lightning Protection Systems.

Reply to
glen walpert

Danger: if the hardware is specified torqued dry, you'll get way too much clamping force (easily to the point of deformation) with greased threads!

Per spec of course is just what you want, no more and no less. If mfg doesn't say to grease the bolt, say -- don't do it!

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: https://www.seventransistorlabs.com/
Reply to
Tim Williams

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