Acorn clamp dissimilar metal

kwired said:
Good question. Looking around I can find similar clamps that say they are rated for copper, galvanized, stainless or steel rods,rebar, etc. which makes sense for the clamp itself that is usually bronze, but what keeps the copper conductor that is in direct contact with the rod from having galvanic corrosion with the steel rod? Most other clamps listed for use with rebar have separate contact surfaces for the rod and the conductor and the rod and conductor are not in direct contact within the clamp.
Click to expand...
Physics wise -- the only thing that keeps the connection from corroding is initially it's gas and water tight, due to the compression face to face copper to steel. That's it.

But we all know that rebar rusts quite quickly even without help, and anything near the ground is going to be wet. Eventually that rust will reduce the margin of contact as it eats between the steel and copper.

Galvanic corrosion happens at very low voltages: like tenths of a volt. And you can easily have that voltage difference between true ground and the GEC. You thus have all the elements of galvanic corrosion. The steel will be the sacrificial anode, the copper and brass will be fine.

en.wikipedia.org

Cathodic protection - Wikipedia

en.wikipedia.org en.wikipedia.org

In field inspections this effect is very pronounced near water heaters (inside and out). Encased in concrete who knows? Concrete is porous to water vapor and moisture and is conductive. Maybe we just throw away buildings in the USA too fast to notice. Go to the UK with 900 year old pubs and inns, and find the one with the oldest ground connection and check.....
 
Russell Ensslin said:
Does anyone know if there is an NEC dissimilar metals rule?
Click to expand...
Whether contact between dissimilar metals is subject to corrosion depends on which metals you are talking about. Copper to aluminum contact is a bad combination outdoors.
 
When it comes to the connection to rebar with an acorn there is really no concern for corrosion between the copper and the steel. The reason being if you look at how they're connected together there is more surface contact between the acorn and the copper conductor than there is to the rebar. On the other side of the acorn the bolt (when properly tightened) is actually digging into the metal of the rebar. So even if there were a somewhat poor connection between the rebar and the copper the conductor is still adequately connected to the rebar through tightening of the acorn.
 
I braze them together with silver solder and a oxy/acetl torch. then you know 100% the bond won't fail.
 
Yup. I don't have a cad weld kit. So I braze. It's solid. Any inspector who understands silver solder at high temp knows is a lifetime bond.

There is a special solder for bonding ferrous to non-ferrous. It has a special blue flux on the rod
 
herding_cats said:
Yup. I don't have a cad weld kit. So I braze. It's solid. Any inspector who understands silver solder at high temp knows is a lifetime bond.

There is a special solder for bonding ferrous to non-ferrous. It has a special blue flux on the rod
Click to expand...
Without listing for the specific application most inspectors will turn it down even if they understand.
 
jim dungar said:
Do you really think all it takes to get a product Listed is some money?

Have you tried reading the listing requirements?
Remember, listing is not about quality, it is about meeting industry standards.
Click to expand...
I didn't necessarily mean money under the table, but if they can convince them it meets the listing requirements then it will pass the listing. AFCI manufacturers are good at convincing listing and code people to understand their theories but it does take some money, at the very least all the time put into coming up with their theories and demonstrations. Then there is cases when there is no existing listing standard when something new comes along. Who makes the standards? Likely whoever developed the new item is pretty involved in coming up with standards. And this stuff is becoming more like politics as time goes along, whoever invests enough time and money gets what they want or at least compromises do end up leaning their direction more than opposition direction in many cases.

This sort of thing goes on in approval of things in other industries as well and is getting worse over time.
 
kwired said:
...but if they can convince them it meets the listing requirements then it will pass the listing.
Click to expand...
No.
The item has to actually be submitted for and pass the tests. It is not a simple provide your own documentation.

The issue with AFCI is the testing standard itself. Standards are created by UL. Sometimes standards are created, then someone builds a product. Other times products have been built and are in the market place before a standard exists.
 
kwired said:
Without listing for the specific application most inspectors will turn it down even if they understand.
Click to expand...
I had a plumber saw right through my ground wire on a 600A service pre inspection. Silver soldered it back and had inspection. Inspector asked me if it was plumbing solder. I said hell no, I know better than that. 15% silver hot solder. He was totally fine with it.
 
You must log in or register to reply here.
Top